EPA-600/2-76-291
December 1976
Environmental Protection Technology Series
EFFECTS OF IRRIGATION METHODS ON
GROUNDWATER POLLUTION BY
NITRATES AND OTHER SOLUTES
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
-------
EPA-600/2-76-291
December 1976
EFFECTS OF IRRIGATION METHODS ON GROUNDWATER
POLLUTION BY NITRATES AND OTHER SOLUTES
by
Charles W. Wendt
Arthur B. Onken
Otto C. Wilke
Texas Agricultural Experiment Station
Lubbock, Texas 79401
Ronald D. Lacewell
Texas A&M University
College Station, Texas 77843
Grant No. S-802806
(Formerly 13030EZM)
Project Officer
James P. Law, Jr.
Source Management Branch
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
-------
DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection Agency,
nor does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
-------
ABSTRACT
Sprinkler irrigation, furrow irrigation, subirrigation, automated
subirrigation, criteria for applying irrigation water, methods of applying
fertilizer and sources of fertilizer were investigated as to their potential
to decrease possible pollution from nitrate and other solutes in a loamy fine
sand soil overlying a shallow aquifer in Knox County, Texas.
Less nitrate-nitrogen was available for leaching in subirrigation
systems than furrow and sprinkler systems. Less irrigation water was
applied with automated subirrigation systems than with the other irriga-
tion systems. However, crop water requirement was not significantly
changed—the soil water was more efficiently used. Fertilizer remained
in the root zone if the water applied was based on potential evapotrans-
piration and leaf area regardless of the irrigation system or the criteria
used to apply the irrigation water. Banded fertilizers moved differently
in the different irrigation systems.
Subirrigation has the possibility of having irrigation return flow
with lower concentrations of other solutes than sprinkler or furrow
systems.
Banding fertilizer in the bed was superior to banding below the level
of the water furrow and applications in the irrigation water relative to
quality of irrigation return flow. No one source of nitrogen fertilizer
was indicated to be superior.
Current fertilization practices are not causing major increases in
the nitrate-nitrogen level in the aquifer.
This report was submitted in fulfillment of Grant No. S-802806 (formerly
13030 EZM) by the Texas Agricultural Experiment Station under the sponsor-
ship of the U.S. Environmental Protection Agency. This work covers the
period June 23, 1970 to August 31, 1976, and work was completed as of
January 30, 1976.
111
-------
CONTENTS
Abstract iii
Figures vi
Tables xxiil
Acknowledgments xxvii
1. Introduction 1
2. Conclusions 5
3. Recommendations 8
4. Materials and Methods 10
5. Experimental Phase. 33
6. Results and Discussion 116
Objective 1 - Contribution of Current Irriga-
tion and Fertilization Practices to Pollution
of Underground Water 116
Objective 2 - Potential of Using Modified Cur-
rent Irrigation and Fertilization Practices for
Immediate Reduction of Potential Pollution 198
Objective 3 - Potential of Using Subirrigation
for More Efficient Water Application and New
Systems of Fertilization for Long-Range Solu-
tions to the Pollution Problem 226
Objective 4 - Economics of Installation, Opera-
tion and Maintenance of Subirrigation Systems
and of Each Fertilization Practice 304
7. Summary 322
References 327
Publications and Presentations 329
-------
FIGURES
Number
1 Location of vacuum, electrical , meteorological , and
irrigation installations at the field site near
Munday, Texas .....
Transmissibility of the Seymour aquifer under the site
near Munday, Texas, 1970 ..... .
3 Moisture increase (percent by volume) and distribution
62 hours after subirrigation in a Miles loamy fine sand
located on the site near Munday, Texas ............ 14
4 Location of instrumentation in each plot at field site
near Munday, Texas. Plots are 16 rows wide (102-cm
centers) by 67 m long. Underground vacuum line is
15.2 m from each end of plot. Soil instrumentation
layouts for Locations 1 and 2 are shown in Figures 5
and 6 .... ....... . ............. ... 15
5 Soil instrumentation layout in Location 1 in each plot of
the field site near Munday, Texas. Depth of each instru-
ment is as indicated. (Depths and dimensions in meters.). . . 17
6 Soil instrumentation layout at Location 2 in each plot of
the field site near Munday, Texas. Depth of each instru-
ment is as indicated. (Depths and dimensions in meters.). . . 18
7 Plot design used in hydraulic conductivity studies in Knox
County, Texas. (Tensiometers spaced at 0.3-m intervals at
random depths to 3.0 m around each access tube. Neutron
access tubes spaced 2.1 m apart in an equilateral tri-
angle to 3.7-m depth.) .... ................ 22
8 Subirrigation system layout at the field site at Lubbock,
Texas. Each plot is 16 rows wide (102-cm centers) by
67 m long ....... . ................... 31
9 Schematic of orifice inserted in plastic pipe in subirri-
gation systems at Munday and Lubbock, Texas .......... 32
10 Clay content between the surface and the water table at
the south end of the water quality research site at
Munday, Texas ......... . ............... 40
vi
-------
FIGURES (Continued)
Number Page
11 Clay content between the surface and the water table at
the north end of the water quality research site at
Munday, Texas 41
12 Bulk density between the surface and the water table of
the north end of the field site, Munday, Texas 42
13 Maximum and minimum total and matric potential-depth
curves and clay percentage of selected plots in the
various irrigation systems 50
14 Relationship between 6 and count ratio for Troxler
neutron moisture probe No. 1 used at the field site
near Munday, Texas 52
15 Relationship between 0 and count ratio for the Troxler
neutron probe No. 2 used at the field site near
Munday, Texas 53
16 Relationship between 9/count ratio and bulk density
for Troxler neutron probe No. 1 used at the field
site near Munday, Texas 54
17 Relationship between 6/count ratio and bulk density
for Troxler neutron probe No. 2 used at the field
site near Munday, Texas 55
18 Relationship between counts and wet density for the
Troxler density probe used to determine the bulk
densities of the field site near Munday, Texas 56
19 Comparison of uncorrected values for 0 using the standard
curve from the Company and corrected values for 6 using
the curve developed from standards made of soils at the
site having different bulk densities 57
20 Relationship between 0 and probe reading for the
Reconnaissance probe on loan from the U. S. Environmental
Protection Agency 58
21 Relationship between 0/meter reading and density for the
Reconnaissance probe 59
22 Maximum and minimum soil-water contents of profiles from
the different irrigation systems during 1972 62
23 Changes in soil-water content in a sprinkler-irrigated
plot during the course of the study 63
vii
-------
FIGURES (Continued)
Jumber
24 Hydraulic conductivity vs soil-water content for various
depths in a Miles loamy fine sand in Knox County,
Texas, 1973 - 74
25 Hydraulic conductivity vs soil-water content at different
times for the 76- and 229-cm depths in a Miles loamy
fine sand '5
26 Hydraulic conductivity vs metric suction at different times
for the 76- and 229-cm depths in a Miles loamy fine
sand 76
27 Hydraulic head at different depths on various dates in
Plot 3 in Miles loamy fine sand soil. 77
28 Cumulative ET potential following emergence of the first
corn crop planted 1971-1974 80
29 Concentrations of nitrate-N, chloride and sulfate in a
furrow-irrigated plot (Plot 20) in 1:1 extracts of core
samples at the beginning of the growing season (curve 1)
and end of growing season (curve 2) and in vacuum
samples at the end of the growing season (curve 3), 1971. . . 85
30 Concentrations of magnesium, ammonium and potassium in a
furrow-irrigated plot (Plot 20) in 1:1 extracts of core
samples at the beginning of the growing season (curve 1)
and end of growing season (curve 2) and in vacuum
samples at the end of the growing season (curve 3), 1971. . . 86
31 Concentrations of calcium, sodium and conductivity in a
furrow-irrigated plot (Plot 20) in 1:1 extracts of core
samples at the beginning of the growing season (curve 1)
and end of growing season (curve 2) and in vacuum
samples at the end of the growing season (curve 3), 1971. . . 87
32 Comparison of nitrate-N concentrations of vacuum soil-water
samples and 1:1 extracts of soil samples for various
depths, Plot 20, Location 1. Field site near Munday,
Texas, 1971 88
33 Concentrations of bromide and nitrate-N in porous bulb
soil-water extracts obtained from the sprinkler-
i-Tigated plots, 1972 ......... 91
34 Concentrations of bromide and nitrate-N in 1:1 extracts
of core samples obtained from the sprinkler-irrigated
plots, 1972 „ 92
vi ii
-------
FIGURES (Continued)
Number Page
35 Concentrations of bromide and nitrate-N in porous bulb
soil-water extracts from the furrow-irrigated plots,
1972 93
36 Concentrations of bromide and nitrate-N in 1:1 extracts of
core samples obtained from the furrow-irrigated plots,
1972 94
37 Concentration of bromide in porous bulb soil-water extracts
and 1:1 extracts of core samples obtained from the sub-
irrigated plots, 1972 95
38 Concentration of chloride in porous bulb soil-water extracts
of samples obtained from furrow, sprinkler, and subirri-
gated plots, 1972 97
39 Concentrations of chloride in 1:1 extracts of core samples
obtained from the furrow, sprinkler, and subirrigated
plots, 1972 98
40 Symbol key for Figures 41 through 46 99
41 Areas of significant concentrations of bromide, nitrate-N
and chloride in a sprinkler-irrigated plot (Plot 10-1)
81 days after application of bromide, 1972 100
/•
42 Areas of significant concentrations of bromide, nitrate-N
and chloride in a sprinkler-irrigated plot (Plot 10-2)
81 days after application of bromide, 1972 102
43 Areas of significant concentrations of bromide, nitrate-N
and chloride in a furrow-irrigated plot (Plot 21-1)
81 days after application of bromide, 1972 103
44 Areas of significant concentrations of bromide, nitrate-N
and chloride in a furrow-irrigated plot (Plot 21-2)
81 days after application of bromide, 1972 104
45 Areas of significant concentrations of bromide, nitrate-N
and chloride in a subirrigated plot (Plot 36-1) 81 days
after application of bromide, 1972 105
46 Areas of significant concentrations of bromide, nitrate-N
and chloride in a subirrigated plot (Plot 36-2) 81 days
after application of bromide, 1972 106
-------
FIGURES (Continued)
Number
47 Soil-water potential (cb) on selected dates in the -30 cb
plot before and after irrigating with 2.8 cm of water
between August 3 and August 9 in 1971 at Lubbock, Texas ... 109
48 Soil-water potential (cb) on selected dates in the -60 cb
plot before and after irrigating with 2.8 cm of water
between August 3 and August 9 in 1971 at Lubbock, Texas ... 110
49 Soil-water content on selected dates before and after
irrigation (2.8 cm of water applied between August 3
and August 9) in 1971 at Lubbock, Texas Ill
50 Cumulative amounts of applied water and potential evapo-
transpiration [Jensen, et al. (10)] from the automated
subirrigated plots at Lubbock, Texas, during 1972 115
51 Phosphate concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 117
52 Chloride concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 118
53 Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system 120
54 Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system 121
55 Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system 122
56 Chloride concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system 123
57 Sulfate concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 125
58 Sulfate concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system 126
-------
FIGURES (Continued)
Number Page
59 Sulfate concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system 127
60 Sulfate concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system 129
61 Sulfate concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system 130
62 Sodium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 131
63 Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system .......... 132
64 Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system 134
65 Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system . 135
66 Sodium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system 136
67 Calcium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 137
68 Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system 138
69 Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system . 140
70 Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system 141
-------
FIGURES (Continued)
Number Pa9e
71 Calcium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system '^2
72 Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a sprinkler
irrigation system 143
73 Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a furrow irri-
gation system 144
74 Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a manual sub-
irrigation system 146
75 Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system 147
76 Potassium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system 148
77 Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system 149
78 Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system 150
79 Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system 152
80 Potassium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system 153
81 Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler-irrigated
plot fertilized with Uran banded in the bed 154
82 Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler-irrigated plot fertilized with Uran banded in
the bed 155
xii
-------
FIGURES (Continued)
Number Page
83 Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow-irrigated plot fertilized with Uran banded in the
bed 156
84 Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manually-subirrigated plot fertilized with Uran banded in
the bed 157
85 Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irrigation
system 159
86 Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a sprin-
kler irrigation system 160
87 Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a fur-
row irrigation system 161
88 Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system 162
89 Electrical conductivity of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system. .... 163
90 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot 164
91 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot . 165
92 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot 166
93 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot. . . 168
94 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot. . . 169
95 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot. . . 170
-------
FIGURES (Continued)
Number Page
96 Porous bulb soil-water extract m'trate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded below the level of the water furrow 171
97 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with anhydrous ammonia banded below the level of the
water furrow 172
98 Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and plot with anhydrous
ammonia banded in the bed below the bottom of the water
furrow, 1973. (Total N - 374 kg/ha). 173
99 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran banded
below the level of the water furrow 175
100 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded below the level of the water furrow 176
101 Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and plot treated with Uran
banded in the bed below the bottom of the water furrow,
1973. (Total N - 368 kg/ha) 177
102 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran
applied in the irrigation water ..... 178
103 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water 179
104 Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and a plot treated with
Uran for three years, 1973. (Total N - 375 kg/ha). ..... 180
105 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran
applied in the irrigation water 181
106 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water 182
xiv
-------
FIGURES (Continued)
Number Page
107 Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and plot treated with Uran
for three years, 1973. (Total N - 364 kg/ha) 183
108 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974 185
109 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974. 186
110 Comparison of predicted values of soil nitrate with measured
values at a depth of 30 cm. Values plotted are the aver-
age of two locations 190
111 Relationship between leachate concentrations, excess water
additions, and fertility levels. Irrigations were applied
when the net evapotranspiration was 20 mm 192
112 Relationship between leachate concentrations, excess water
additions, and fertility levels. Irrigations were applied
when the net evapotranspiration was 60 mm 193
113 Decision flow chart for limiting leaching of nitrate-N from
sandy soils 196
114 Relationship between depth of bromide and water added in
excess of evapotranspiration and evaporation 197
115 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded in the bed 199
116 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with anhydrous ammonia banded in the bed 200
117 Porous bulb soil-water extract nitrate-N concentrations by
soil depth for plots treated with anhydrous ammonia banded
at different depths for three years, 1973. (Total N -
374 kg/ha) 202
118 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974 203
xv
-------
FIGURES (Continued)
Number
119 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran
banded in the bed .. ................. •
120 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed ................. 205
121 Porous bulb soil -water extract nitrate-N concentrations by
soil depth for plots treated with Uran banded at different
depths for three years, 1973. (Total N - 368 kg/ha) ..... 206
122 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974 .................. ....... 208
123 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-
coated urea banded in the bed ...... . ......... 209
124 Porous bulb soil -water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with sulfur-coated urea banded in the bed .......... 210
125 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with anhydrous
ammonia banded in the bed .................. 211
126 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with anhydrous
ammonia + N-Serve banded in the bed ............. 212
127 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded in the bed .................. 213
128 Porous bulb soil -water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with anhydrous ammonia banded in the bed ........ ... 214
129 Porous bulb soil -water extract nitrate-N concentrations by
soil depth for a control plot and plot treated with
anhydrous ammonia for three years , 1973. (Total N -
374 kg/ha) ............. . ...... ....... 216
130 Porous bulb soil -water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran banded
in the bed .......................... - 217
xvi
-------
FIGURES (Continued)
Number
131
132
133
134
135
136
137
138
139
140
141
142
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-
coated urea banded in the bed
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with sulfur-coated urea banded in the bed
218
219
220
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of sulfur-
coated urea application and irrigated by different
systems, 1974. (Total N - 518 kg/ha)
221
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed and irrigated when signifi-
cant leaf curl occurred
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed and irrigated when the tensi-
ometer reached -20 cb potential
223
224
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed and irrigated when the tensi-
ometer reached -40 cb potential
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972 for a control plot
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot. .
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972-1973 for a control plot
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran applied
in the irrigation water
225
227
228
229
230
232
xvn
-------
FIGURES (Continued)
Number
143 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972 for a plot treated with Uran
applied in the irrigation water 233
144 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water 234
145 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972-1973 for a plot treated with Uran
applied in the irrigation water 235
146 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with ammonia
banded in the bed 236
147 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with ammonia banded in the bed 237
148 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran
banded in the bed , . 238
149 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972 for a plot treated with Uran
banded in the bed 239
150 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed 240
151 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972-1973 for a plot treated with Uran
banded in the bed 241
152 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-
coated urea banded in the bed 243
153 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with sulfur-coated urea banded in the bed 244
154 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with ammonia +
N-Serve banded in the bed 245
xvm
-------
FIGURES (Continued)
Number page
155 Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with ammonia
banded in the bed 246
156 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974. (Total N - 514 kg/ha) 247
157 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974. (Total N - 508 kg/ha) 248
158 Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N appli-
cation, 1974. (Total N - 518 kg/ha) 249
159 Concentrations of nitrate-N from all sources by depth in
1973 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Sprinkler-irrigated) 251
160 Concentrations of nitrate-N from all sources by depth in
1974 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Sprinkler-irrigated) 252
161 Concentrations of nitrate-N from all sources by depth in
1973 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Furrow-irrigated) 253
162 Concentrations of nitrate-N from all sources by depth in
1974 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Furrow-irrigated) 255
163 Concentrations of nitrate-N from all sources by depth in
1973 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Subirrigated) 256
164 Concentrations of nitrate-N from all sources by depth in
1974 for plots treated with 15N-enriched sodium nitrate
banded in the bed. (Subirrigated) 257
165 Concentrations of fertilizer nitrate-N by depth in 1973
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Sprinkler-irrigated) 258
166 Concentrations of fertilizer nitrate-N by depth in 1974
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Sprinkler-irrigated) 259
xix
-------
FIGURES (Continued)
Number
167 Concentrations of fertilizer nitrate-N by depth in 1973
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Furrow-irrigated) 261
168 Concentrations of fertilizer nitrate-N by depth in 1974
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Furrow-irrigated) 262
169 Concentrations of fertilizer nitrate-N by depth in 1973
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Subirrigated) 263
170 Concentrations of fertilizer nitrate-N by depth in 1974
for plots treated with 15N-enriched sodium nitrate banded
in the bed. (Subirrigated) 264
171 Percent nitrate-N from fertilizer by depth in 1973 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Sprinkler-irrigated) 265
172 Percent nitrate-N from fertilizer by depth in 1974 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Sprinkler-irrigated) 266
173 Percent nitrate-N from fertilizer by depth in 1973 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Furrow-irrigated) 268
174 Percent nitrate-N from fertilizer by depth in 1974 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Furrow-irrigated) 269
175 Percent nitrate-N from fertilizer by depth in 1973 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Subirrigated) 270
176 Percent nitrate-N from fertilizer by depth in 1974 for plots
treated with 15N-enriched sodium nitrate banded in the
bed. (Subirrigated) 271
177 Dry matter production, total nitrogen and fertilizer nitrogen
in the tops of sprinkler-irrigated sweet corn fertilized
with 15N-enriched sodium nitrate, 1973 277
178 Dry matter production, total nitrogen and fertilizer nitrogen
in the tops of Subirrigated sweet corn fertilized with
15N-enriched sodium nitrate, 1973 278
xx
-------
FIGURES (Continued)
Number page
179 Dry matter production, total nitrogen and fertilizer nitrogen
in the tops of subirrigated sweet corn fertilized with
15N-enriched sodium nitrate, 1974 279
180 Lateral and vertical distribution of nitrate-N, fertilizer-N
and bromide by date in soil sample extracts from Plot 6-1.
(Sprinkler-irrigated - fertilized with 15N-enriched sodium
nitrate) 289
181 Lateral and vertical distribution of nitrate-N, fertilizer-N
and bromide by date in soil sample extracts from Plot 18-1.
(Furrow-irrigated - fertilized with 15N-enriched sodium
nitrate) 290
182 Lateral and vertical distribution of nitrate-N, fertilizer-N
and bromide by date in soil sample extracts from Plot 32-1.
(Subirrigated - fertilized with 15N-enriched sodium
nitrate) 291
183 Water potential measured at 0.3 m during the growing season
of 1972 for plots fertilized with Uran, planted to sweet
corn and irrigated by three methods 293
184 Water potential measured at 0.3 m during the growing season
of 1972 for plots fertilized with sodium nitrate and sodium
bromide, planted to sweet corn and irrigated by three
methods 294
185 Water potential measured at 0.3 m during the growing season
of 1974 for plots fertilized with 15N-enriched sodium
nitrate, planted to sweet corn and irrigated by three
methods 295
186 Changes in soil-water content with depth between the begin-
ning and end of the growing season in the furrow- and
sprinkler-irrigated plots in the 1973 irrigation systems
study, Knox County, Texas 300
187 Changes in soil-water content with depth between the begin-
ning and end of the growing season in the manually- and
automatically-subirrigated plots in the 1973 irrigation
systems study in Knox County, Texas 301
188 Potential vs measured evapotranspiration of sweet corn irri-
gated with various irrigation systems in Knox County,
Texas, 1973 302
xxi
-------
FIGURES (Continued)
Number Page
189 Leaf area index of sweet corn produced with various irri-
gation systems, Knox County, Texas, 1973 303
190 Plant evaporation (Ep) of sweet corn produced with different
irrigation systems in relation to potential evaporation
(Eo) as influenced by leaf area index 305
191 Yield of sweet corn of different irrigation systems as influ-
enced by different irrigation criteria, 1971-1974, Knox
County, Texas 313
192 Yield of sweet corn from different irrigation systems as
influenced by fertilizer source and method of applica-
tion, 1971-1974, Knox County, Texas 314
193 Yield of sweet corn per cm water as influenced by different
criteria for applying irrigation water, 1971-1974, Knox
County, Texas 316
194 Yield of sweet corn per cm of water of different irrigation
systems as influenced by different fertilizer sources and
methods of application, 1971-1974, Knox County, Texas .... 317
195 Yield of sweet corn of different irrigation systems per kg
of nitrogen applied at the 100 kg/ha rate as influenced
by different irrigation criteria, 1971-1974, Knox
County, Texas 318
196 Yield of sweet corn of different irrigation systems per kg
of nitrogen applied at the 100 kg/ha rate as influenced
by different fertilizer sources, 1971-1974 320
197 Yield of sweet corn of different irrigation systems per kg
of nitrogen applied at the 22.5 kg/ha rate as influenced
by the different irrigation criteria, 1971-1974 321
xx-n
-------
TABLES
Number page
1 Fertilizer and Irrigation Treatments for the 1971-1974
Crop Years at the Knox County, Texas, Field Site 25
2 Pertinent Planting, Pesticide Applications, and Harvesting
Information, 1971-1974 34
3 Fertilizer Sources, Rates (kg/ha) and Dates of Application,
1971-1974, in Knox County, Texas 36
4 Percent of Emitters in Automated Subirrigation Plots Plugged
After One Season of Use 44
5 Summary of the Amounts of Water Applied at Each Irrigation
to the Different Plots at the Field Site Near Munday,
Texas, 1971-1974- ...... 45
6 Amounts of Water Applied Prior to Emergence to the Different
Plots at the Field Site Near Munday, Texas, 1971-1974 .... 46
7 Amounts of Water Applied (cm) During the Growing Season to
the Different Plots at the Field Site Near Munday, Texas,
1971-1974 48
8 Characteristics of Standards Used to Calibrate Neutron
Probes 58
9 Comparison of Moisture Content (Percent by Volume) Values
Obtained by a Troxler Neutron Probe and a Well
Reconnaissance, Inc., Neutron Probe 60
10 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During September 18
to October 3, 1973 and October 8 to October 29, 1973 at
Location 1 65
11 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During September 21
to October 5, 1973, Location 2 66
12 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During September 21
to October 5, 1973, Location 3 67
xxm
-------
TABLES (Continued)
Number Pag
13 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During August 7 to
September 6, 1974, Location 1 68
14 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During August 7 to
September 6, 1974, Location 2 70
15 Hydraulic Conductivity Data and Values Obtained for a Miles
Loamy Fine Sand, Knox County, Texas, During August 7 to
September 6, 1974, Location 3 72
16 Monthly Rainfall Received at the First Field Site, Knox
County, Texas, 1971-1974 82
17 Dates on Which Soil-Water Extracts Were Obtained From the
Various Plots in Knox County, Texas, 1971-1974 84
18 Centimeters of Irrigation Water Applied Automatically to
Subirrigation Plots at Lubbock, Texas, During 1971 108
19 Rainfall Received at Lubbock, Texas, Between the Emergence
and Harvest of the 1972 Crop 113
20 Irrigation Water Applied Automatically to Subirrigation
Plots at Lubbock, Texas, During 1972 114
21 Various Input Conditions Modeled 191
22 Minimum Levels of Fertility for Ample Plant Nitrogen
(Plants Used 164.35 kg of Nitrogen per ha) 194
23 Yield and Irrigation Application Data of Treatments
Sprinkler-Irrigated by Different Criteria 222
24 Plant Growth and Nitrogen Data for the Top Growth of
Sprinkler-Irrigated Sweet Corn Grown on Plots Fertil-
ized Two Years with 15N-enriched Sodium Nitrate, 1974 .... 273
25 Fertilizer Nitrogen Found in Two Nitrogen Fractions of
Soil Samples From Plots Fertilized Two Years With 15N-
enriched Sodium Nitrate and Cropped With Sweet Corn
Irrigated by Three Systems, Location 1 274
26 Plant Growth and Nitrogen Data for the Top Growth of
Sprinkler-Irrigated Sweet Corn Fertilized With 15N-
enriched Sodium Nitrate, 1973 275
xxiv
-------
TABLES (Continued)
Number
27 Fertilizer Nitrogen Data for the Top Growth of Two
Crops of Irrigated Sweet Corn Fertilized With 15N-
enriched Sodium Nitrate 276
28 Nitrate-N Concentration (ppm) at Selected Depths From a
Sprinkler-Irrigated Plot (Location 1) at the Field
Site Near Munday, Texas, on August 8, 1972 282
29 Nitrate-N Concentration (ppm) at Selected Depths From a
Sprinkler-Irrigated Plot (Location 2) at the Field
Site Near Munday, Texas, on August 8, 1972 282
30 Nitrate-N Concentration (ppm) at Selected Depths From a
Furrow-Irrigated Plot (Location 1) at the Field Site
Near Munday, Texas, on August 8, 1972 283
31 Nitrate-N Concentration (ppm) at Selected Depths From a
Furrow-Irrigated Plot (Location 2) at the Field Site
Near Munday, Texas, on August 8, 1972 283
32 Nitrate-N Concentration (ppm) at Selected Depths From a
Subirrigated Plot (Location 1) at the Field Site Near
Munday, Texas, on August 8, 1972 284
33 Nitrate-N Concentration (ppm) at Selected Depths From a
Subirrigated Plot (Location 2) at the Field Site Near
Munday, Texas, on August 8, 1972 284
34 Bromide Concentration (ppm) at Selected Depths From a
Sprinkler-Irrigated Plot (Location 1) at the Field
Site Near Munday, Texas, on August 8, 1972 285
35 Bromide Concentration (ppm) at Selected Depths From a
Sprinkler-Irrigated Plot (Location 2) at the Field
Site Near Munday, Texas, on August 8, 1972 285
36 Bromide Concentration (ppm) at Selected Depths From a
Furrow-Irrigated Plot (Location 1) at the Field
Site Near Munday, Texas, on August 8, 1972 286
37 Bromide Concentration (ppm) at Selected Depths From a
Furrow-Irrigated Plot (Location 2) at the Field
Site Near Munday, Texas, on August 8, 1972 286
38 Bromide Concentration (ppm) at Selected Depths From a
Subirrigated Plot (Location 1) at the Field Site
Near Munday, Texas, on August 8, 1972 287
XXV
-------
TABLES (Continued)
Number Page
39 Bromide Concentration (ppm) at Selected Depths From a
Subirrigated Plot (Location 2) at the Field Site Near
Munday, Texas, on August 8, 1972 287
40 Nitrogen Concentrations (ppm) of Soil-Water Extracts
From Porous Bulb Samples. Subirrigated Plot, 1972 288
41 Criteria for Applying Irrigation Through the Various
Systems in a Comparison of the Water Efficiency of
Irrigation Systems in Knox County, Texas, 1973 297
42 Rainfall Received and Irrigation Water Applied to
Selected Plots in the Various Irrigation Systems
in Knox County, Texas, in 1973 299
43 Per Hectare Yield and Expected Net Returns for Sweet
Corn by Research Plot: 1971-1973 307
44 Per Hectare Yield and Expected Net Returns for Sweet
Corn for Alternative Fertilizer Rates and Methods
of Applying Irrigation Water, 1971-1973 309
45 Estimated Per Hectare Subirrigation Investment Where Net
Returns Would be Equal to Net Returns for Sprinkler
and Furrow Irrigation Based on 1971-1973 Data 311
46 Estimated Per Hectare Subirrigation Sweet Corn Yield
Where Net Returns Would be Equal to Net Returns for
Sprinkler and Furrow Irrigation Based on 1971-1973
Data 312
xxvi
-------
ACKNOWLEDGMENTS
The authors are indebted to many individuals for their contributions to
this study. Major contributions were made by Mr. Walter Bausch, Mr. Larry
Barnes, and Mr. Raford Hargrove in operating field and laboratory facilities
at Munday. Mrs. Marty Hyde contributed in many ways to the financial and
reporting aspects of the report.
The study was supported by the U. S. Environmental Protection Agency
under Programs 13030EZM and S802806, Dr. J. P. Law, Project Officer; by The
Texas Agricultural Experiment Station at two locations: Texas A&M University
Vegetable Research Center at Munday, Texas, Dr. M. C. Fuqua, Director; and
Texas A&M University Agricultural Research and Extension Center at Lubbock,
Texas, Dr. George G. McBee and Dr. Bill Ott, Resident Directors of Research;
and by the Texas Water Resources Institute, Dr. J. R. Runkles, Director.
xxv ii
-------
SECTION 1
INTRODUCTION
Irrigated agriculture is the major consumer of water in the western
United States. With the increasing demand for water for municipal and
industrial needs, there is increasing concern about the influence of
irrigated agriculture on the quality of the nation's water resources.
Water applied in irrigated agriculture may evaporate from the soil or
crop surface or leave the area of application as runoff or leachate.
The water leaving the area of application may be degraded due to a high
concentration of mineral salts from soil water evaporation and plant
transpiration. Law (15) notes in his summary that 20-fold increases in
mineral content have been noted in the Colorado and Rio Grande Rivers due
to the low quality of irrigation return flows.
Intensification of crop production has resulted in increased applica-
tions of nitrogen fertilizer. In many cases, the amount of fertilizer
applied is in excess of that required by the crop. This excess, along with
nitrate available from nitrification, may be leached from the root zone if
water is applied in excess of that required by the crop. Water containing
greater than 45-ppm nitrate or 10-ppm nitrogen as nitrate is considered a
hazard to animal life by causing methemoglobinemia (4,16).
Many irrigated areas have geological and soil characteristics which
favor water losses through irrigation return flows that are of poor
quality. These areas include the Platte River Valley in Nebraska, the
Helena Valley in Montana and the San Luis Valley in Colorado, as well as
the Colorado River Valley previously mentioned.
Another such area is the Seymour water-bearing formation in Texas (19),
The formation underlays 1120 sq km in Knox and Haskell Counties in the
Rolling Plains of Texas. Groundwater in the formation is derived solely
from precipitation (25 to 102 cm per year) on the outcrop within the two
counties. Prior to 1900 the Seymour formation was nearly dry. It was
filled with water between 1900 and 1935 when the rainfall was generally
above normal, and a large part of the land was cleared of its native grass
vegetation and placed in cultivation. The water level in one well in this
formation rose 18.4 m during this 35-year period. A majority of the wells
are drilled to a depth of only 9.1 to 21.3 m. The static water level
varies from ground level to a depth of 9.1 m. The water table slopes
generally 2.4 to 3.0 m per kilometer toward the northeast. Water is
discharged into the Brazos River through numerous springs and seeps.
-------
The water in the Seymour formation contains a large amount of nitrate-
nitrogen (nitrate-N). The nitrate-N content of 62 samples of groundwater
taken from this aquifer in 1962 ranged from 21- to 183-ppm nitrate with 39
exceeding the recommended Department of Health limit of 45 ppm. The cities
of Haskell, Rule, Rochester, O'Brien, Knox City, Munday, Goree, Rhineland,
and Weinert all use the formation for a water supply and none have an
approved water supply. Haskell, Knox City, Munday, and Goree have formed
a water district to obtain a surface water supply; however, the Seymour
formation is the only source of water for the other small towns and farm-
steads of the area.
Initially, the high nitrate-N in the water may have been due to leach-
ing of nitrates from the grassland when it was put in cultivation. Inor-
ganic nitrogen does not accumulate under grassland due to slow rates of
mineralization; however, total nitrogen accumulations are highest under
grass vegetation. Most of this nitrogen is bound in organic form. When
placed under cultivation, organic nitrogen in such soils decreases rapidly
due to mineralization. Total nitrogen also decreases due to crop removal
and leaching of the inorganic nitrogen. In a sandy soil, nitrates have
been shown to move downward 45 cm with a 10-cm application of water (7).
Nitrate levels of 200 ppm have been found to accumulate during the break-
down of organic residues.
Since 1951, the area has been changing from a dryland agriculture to
an irrigated agriculture. Between 1951 and 1968, the number of irrigation
wells increased from 25 to over 2,000 (17). With increasing irrigation,
there have also been increases in fertilization. There is some indication
that the nitrate-N level of the wells of the area is increasing. According
to analyses from the Texas State Department of Health Laboratories, nitrate
in the city well of O'Brien rose from 67 to 165 ppm between 1960 and 1965.
There is some question with respect to the contribution of nitrogen
fertilization to the above-mentioned increases in nitrate-N in the water
table. In 1970, a cooperative project between the Environmental Protection
Agency and the Texas Agricultural Experiment Station was approved. In the
project, facilities in Knox and Lubbock Counties, Texas, were used to com-
pare current and new irrigation and fertilization methods to determine the
following:
a. The contribution of current irrigation and fertilization practices
to pollution of underground water.
b. The potential of using modified current irrigation and fertili-
zation practices for immediate reduction of pollution.
c. The potential of using subirrigation for more efficient water
application and new systems of fertilization for long-range solutions to
the pollution problem.
-------
d. The economics of installation, operation, and maintenance of
subirrigation systems as compared to conventional irrigation systems and
economics of each fertilization practice.
From data obtained during the first year of the project, it was noted
that concentrations in excess of 40-ppm nitrate-N occurred in soil-water
extracts from the profiles of unfertilized plots. Therefore, nitrate-N
concentrations in the profiles of fertilized plots were a result of both
soil nitrogen and nitrogen from fertilizers, and it was difficult to assess
separately the contribution of soil nitrogen and fertilizer nitrogen to the
nitrate-N at various depths in the soil profile. Since crops use both
sources of nitrogen and both sources may be contributors of nitrogen to
irrigation return flow, it was necessary to distinguish between the contri-
butions of each source before conclusions concerning the degradation of
irrigation return flows by nitrogen fertilizers could be made.
In 1973, the original project was augmented with a supplementary study
using nitrogen fertilizer tagged with the nitrogen isotope, 15N, with the
following objectives:
a. To determine separately the contributions of soil nitrogen and
fertilizer nitrogen to the nitrogen available to irrigation return flow.
b. To determine the influence of different irrigation systems
(sprinkler, furrow, and subirrigation) on the distribution of soil nitrogen
and fertilizer nitrogen.
Fertilizer enriched with 15N was applied to duplicate plots in the
furrow irrigation, sprinkler irrigation, and subirrigation systems during
the 1973 growing season.
It was difficult to draw any significant conclusions concerning the
behavior of 15N with only one year's data relative to the cycling of crop
residue and movement of the fertilizer remaining in the profile after the
growing season was completed. Another growing season was needed to obtain
this information. Furthermore, analyses during the first three years of
the project showed that nitrate and other solutes are moving below the root
zone. Another year's data from samples procured below the root zone was
needed to further evaluate the movement of the nitrate and other solutes
below the root zone into the underground aquifer. Therefore, a continu-
ation of the project was proposed for 1974 with the following objectives:
a. To determine separately the contributions of soil nitrogen and
fertilizer nitrogen from both previous and current years' fertilizer appli-
cation to nitrogen available to irrigation return flow from sprinkler
irrigation, furrow irrigation, and subirrigation systems.
b. To determine the influence of rainfall and irrigation water
applied through sprinkler irrigation, furrow irrigation, and subirrigation
systems on the movement of nitrate-N and other solutes below the root zone
following treatment with different rates and sources of nitrogen fertilizer.
-------
The study was conducted in an area on which a minimum of research had
been conducted. It was, therefore, necessary to obtain definitive informa-
tion concerning the chemical and physical properties of the soil and
characteristics of the climate as they influence the water available for
irrigation return flow. Models used during the course of the study were
either those developed by other researchers or statistical in nature. The
models used are noted in the various sections of the discussion.
-------
SECTION 2
CONCLUSIONS
1. Less nitrate-N is available to be leached from fertilizer applied to
subirrigation systems than sprinkler or furrow irrigation systems.
2. The data indicate that nitrate-N in the immediate zone of the subirri-
gation pipe is denitrified.
3. More nitrogen fertilizer is recovered in plants when applied to
sprinkler systems than the furrow irrigation systems with the lowest
recovery occurring from nitrogen applied to subirrigation systems.
4. Only small amounts of fertilizer nitrogen (2 to 7%) are available to
the following year's crop in loamy fine sand soils.
5. Fertilizer nitrogen remaining in the soil profile at the beginning of
the year following application is primarily in the organic form.
6. Movement of nitrate-N from the root zone was more of a problem between
growing seasons than during growing seasons due to rainfall. During
the growing season it was usually possible to maintain the nitrogen in
the root zone in all irrigation systems by irrigating on the basis of
potential evapotranspiration (ET).
7. Banded fertilizers have unique patterns of movement in each of the
irrigation systems: In sprinkler systems, the fertilizer moves verti-
cally as discrete bands; in furrow irrigation systems, the bands merge
in the bed and move down; in subirrigation systems, the bands move
away from the subirrigation system.
8. Due to the uniqueness of movement of the bands in the different irri-
gation systems, detailed cross sectional soil sampling -is preferable
to porous bulb extracts.
9. Automatic subirrigation systems are superior to manual subirrigation
and sprinkler systems which are superior to furrow irrigation systems
in the amount of irrigation water required to produce corn even if the
manual systems applications are scheduled based on potential ET.
10. No significant differences in total water requirement of corn were
noted between the various irrigation systems. The soil water was
used more efficiently when less irrigation water was applied.
-------
11. Supplemental irrigated areas can increase irrigation water-use
efficiency significantly by utilizing systems so that a portion of the
root zone remains dry for the storage of rainfall.
12. The data indicate that the quality of irrigation return flows of
subirrigation systems will be superior to furrow and sprinkler irriga-
tion systems because the concentrations of all solutes and the elec-
trical conductivity (EC) were lower.
13. A zone low in all solutes is formed in the path of water flow around
the subirrigation pipe.
14. Soil-water content and soil-water potential varied less in the surface
0.3 m in the subirrigation system than in the furrow and sprinkler
irrigation systems.
15. Automated subirrigation systems produce more yield/unit of water but
less total yield than the other irrigation systems.
16. The subirrigation systems currently are beset with too many problems
and are too expensive to be used for low value crops.
17. There is no difference in quality of irrigation return flow and
yield/unit of nitrogen when irrigations at leaf curl, -20 centibars
(cb) and -40 cb potential were compared provided the amount added is
based on potential ET and crop leaf area. Total yield is higher when
the crop is irrigated at -20 cb while yield/unit of water is higher
when the other criteria are used.
18. Banding fertilizer in the bed is superior to banding fertilizer below
the level of the water furrow or applying it in the irrigation water
with respect to nitrate-N in irrigation return flows.
19. No one source of fertilizer was indicated to be better in any way.
20. The soil is too variable to use an analytical model to predict nitrate
and/or solute movement.
21. An empirical model shows that the most important factors affecting
nitrate-N in the leachate are the amount of irrigation water applied
and the nitrate-N in the profile.
22. When irrigation water applied is >2 x potential ET and the nitrate-N
is >200 kilograms per hectare (kg/ha), the leachate will have an
undesirable concentration of nitrate-N (>20 ppm).
23. Bromide can be used as a tracer to indicate nitrate and water movement.
24. For each cm of water added in excess of evaporation and ET, nitrate
moved down 7.4 cm.
-------
25. The variable layered soils are a factor in causing "field capacity" to
be -10 cb rather than the accepted value of -33 cb.
26. Up to 50 kg/ha of nitrogen each year are mineralized from the soil of
the study area.
27. Since the wells received horizontal recharge, potential pollution of
groundwater other than at the site is a possibility.
28. The relationship between the ratio of actual to potential ET and leaf
area index (LAI) is approximately the same for sweet corn, cotton and
sorghum and probably applies to all crops.
29. Because salts are moved upward from subirrigation emitters, periodic
supplemental leaching with another system may be needed in vary arid
areas.
30. Current fertilization practices are not expected to cause dramatic
increases in nitrogen in the aquifer.
-------
SECTION 3
RECOMMENDATIONS
1. Since subirrigation has the potential of enhancing the quality of
irrigation return flows, problems with equipment and plugging should be
solved. Even though it is expensive, it has potential use where the
disposal of high nitrate water is a problem due to the apparent denitri-
fication that occurs with the system.
2. The significant increases in irrigation water-use efficiency and quality
of irrigation return flow suggest that the possibility of automation of
current sprinkler and furrow irrigation systems needs to be investigated
as a practical alternative to improving the quality of irrigation return
flows until automated subirrigation systems become commercially avail-
able.
3. If yields could be substantially increased, the cost of automated
systems could be offset. Current plant varieties have been developed
with current irrigation systems. It is possible that cultivars could
be developed which would respond more positively to the ideal soil
moisture conditions which are available with automated irrigation
systems,
4. If irrigation applications are based on a combination of potential ET
and leaf area development, and only the amount of nitrogen required by
the crop is applied, nitrate-N in irrigation return flows will be
minimal.
5. The growth of longer season crops or double cropping is a possibility
for maintaining nitrate-N in the root zone if water is adequate for
crop growth.
6. In supplemental irrigated areas, modification of current furrow and
sprinkler irrigation systems so that a dry area exists in the root zone
for storage of rainfall would substantially increase irrigation water-
use efficiency.
7. Banding fertilizer in the bed rather than below the level of the water
furrow could be immediately initiated to enhance quality of irrigation
return flows.
8. The low potential (-10 cb) at "field capacity" due to layering is
probably a characteristic of many soils. This creates high water-
holding capacity which is an aid in maintaining quality of
-------
irrigation return flows. A survey of the soils of the U. S. to see
where such characteristics are present would be an aid in developing
management recommendations.
9. A summary of the nitrogen mineralization capability of various soils
would be an aid in modeling and making management decisions relative to
fertilization with nitrogen.
10. Although current fertilization practices are not contributing to the
nitrate-N of the aquifer in the area studied, the possibility exists
if the area were to produce a large acreage of shallow-rooted vegetable
crops which are fertilized heavily and irrigated frequently with
inefficient furrow irrigation systems. Due to the horizontal movement
of water in the aquifer, contamination could easily occur from
locations outside the area of the wells.
11. Due to surface recharge from excess rainfall, the area has the potential
of having a perpetual water supply. A system of monitoring the quality
of current wells and regulating the number of new wells would aid in
maintaining the quality and quantity of the water in the aquifer
indefinitely.
-------
SECTION 4
MATERIALS AND METHODS
MUNDAY LOCATION
Field Site Development
Site Selection--
For this study it was necessary to locate a uniform site of a typical
soil series which had not been irrigated or fertilized. The Miles series
is a loamy sand to fine sandy loam soil (Udic Paleustalfs) common to a large
area of Texas and Oklahoma. However, there was some difficulty in locating
a uniform site of the series because many of the potential sites had 0.2 to
0.4-hectare (ha) areas with a clay lens (>40% clay) at 0.91 to 1.22 m with
the remainder of the sites being typical of the Miles series. A 10.13-ha
site suitable for the study was obtained on the Earl Claburn Farm located
11.3 km west and 2.5 km north of Munday, Texas. A three-year lease was
obtained with the option to renew as long as the Texas Agricultural Exper-
iment Station used the site for-research.
Five test holes were drilled on the site to determine the strata below
the surface and the extent of water-bearing formations. The logs of the
test holes showed that the water-bearing formations began at 7.6 to 10.6 m
below the surface and continued to 13.7 to 16.7 m.
Analyses of the clay fractions were performed by Dr. Joe Dixon,
Professor of Mineralogy, Texas A&M University. Clay fractions from Miles
soil and underlying sediments to 9.1 m were surveyed for mineral content by
x-ray diffraction procedures. Montmorillonite and mica (illite) were the
major components. Montmorillonite and mica occurred as discrete minerals
and in complex interstratified mixtures typical of soils of the region.
Kaolinite and vermiculite were identified in small amounts. Chlorite
occurred sporadically in small amounts. Quartz was present in appreciable
amounts in all clays, and feldspar occurred in small amounts in most
samples. The same suite of clay minerals occurred throughout both 9.1-m
sections. The only depth function observed was the apparent presence of
carbonates or soluble salts indicated by low recovery values for the
particle size determinations at the greatest depths.
Mechanical analyses were made of samples from various layers between
the surface and the water table. The highest clay content of 33.6% occurred
in the 123- to 152-cm layer. Soils in the area with this clay content at
this depth conduct water readily. All samples were either red or brown in
10
-------
color indicating the presence of aerobic rather than anaerobic conditions.
Analyses of saturated extracts made of the samples showed that the
nitrate-N level was rather constant at 4 to 6 ppm and the EC was low (108 to
732 micromhos per centimeter (ymhos/cm). From these preliminary data, it
was concluded that no restricting layers existed between the soil surface
and the water table.
Samples were procured down to 152 cm to determine the fertility status
of the soils. These analyses indicated that the pH, potassium, calcium,
soluble salts and sodium were at levels desirable for plant growth.
Phosphorus additions were indicated to be necessary. The organic matter
was very low, a condition common in the cultivated soils of the area.
Irrigation Well —
To insure a continuous water supply in the event of well or motor
failure, two wells were drilled at the locations indicated on Figure 1.
The 101.60-cm diameter holes were drilled about 18 m deep. Each well was
cased with 45.72-cm diameter steel casing with a 2.4-m length of 0.32-cm
slotted screen and packed with No. 4 gravel. The wells were pumped for
about 48 hours at increasing flow rates.
Aquifer transmissibility is between 3105 hectoliters per day per meter
(hlpd/m) and 4347 hlpd/m. The change in slope of the curve shown in
Figure 2 indicates the wells receive horizontal recharge.
The wells produced increasing amounts of sand as discharge rates were
increased above 1135 liters per minute (1pm). The pumps were, therefore,
designed to produce a maximum of about 1135 1pm per well.
One pump was installed in the west well and two pumps were installed
in the east well. The smaller pump was necessary for the automated subirri-
gation system.
Subirrigation Lateral Spacing--
No criteria existed for determining the proper spacing of subirrigation
laterals in different soil types. Since subirrigation systems have not
previously been evaluated in a Miles fine sandy loam, a preliminary study
was conducted to determine if the spacing proposed was adequate to obtain
good distribution of the water applied. Two polyethylene subirrigation
laterals were buried 30 cm deep and water was applied. Measurements of the
soil water were made with a neutron probe and by gravimetric methods. The
preliminary results (Figure 3) indicated that good soil-water distribution
could be obtained with the laterals on 102-cm centers.
Field Facilities
Field facilities were installed* to undertake the following functions:
a. Extract soil water
b. Measure soil-water potential
c. Measure soil-water content
d. Measure climatic parameters
11
-------
AUTOMATED J
-------
0.0
0.6
1.2
1.8
2.4
3.0
T =
WEST WELL TRANSMISSIBILITY,
Q = 12.10 hl/min
As
I -i
S WHERE Q IS THE PUMPING RATE IN
him AND As IS INCREASE IN DRAWDOWN
BETWEEN 10 AND 100 MINUTES.
3163 hlpd/m
T =
84,500
.76 "
As] = 2.67-1.66 = 1.01
As2 = 2.56-1.80 = 0.76
4 6 10 20
TIME, MIN SINCE PUMPING BEGAN
40 60
100
Figure 2. Transmissibility of the Seymour aquifer under the site near Munday, Texas, 1970.
-------
e. Provide necessary electrical power to operate systems
f. Apply irrigation water
50
LATERAL DISTANCE FROM PIPE, cm
25 0 25 50
75
25 _
50
o
oo
UJ
Q
75
100
OPERATING PRESSURE =0.48 BAR
Figure 3.
Moisture increase (percent by volume) and distribution
62 hours after subirrigation in a Miles loamy fine sand
located on the site near Munday, Texas.
The locations of the field facilities are shown on Figure 1 and
described below.
Soil-Water-Extraction System—
The extraction system was composed of vacuum pumps (Models 1065 and
2065, Gast Manufacturing Company, Benton Harbor, Michigan) and soil-water
extraction tubes (Soil Moisture Equipment Company, Santa Barbara, Califor-
nia) connected by an underground line. The underground vacuum line was
originally 0.64-cm outside diameter (O.D.) nylon line which was installed
at a depth of 76 cm. However, due to high friction losses, the line was
replaced with 1.27-cm O.D. high density polyethylene line. Figure 4
14
-------
UNDERGROUND
VACUUM LINE
L |.J
LOCATION 2
LOCATION 1
UNDERGROUND
VACUUM LINE
Figure 4. Location of instrumentation in each plot at field site
near Munday, Texas. Plots are 16 rows wide (102-cm cen-
ters) by 67 m long. Underground vacuum line is 15.2 m
from each end of plot. Soil instrumentation layouts
for Locations 1 and 2 are shown in Figures 5 and 6.
15
-------
shows the vacuum line in relation to the soil instrumentation in Locations 1
and 2 of each plot.
Twenty-three soil-water extraction tubes were installed in each plot.
Sixteen tubes, ranging in depth from 0.15 to 9.14 m, were installed at Loca-
tion 1 (Figure 5) and seven, ranging in depth from 0.15 to 1.52 m, were
installed at Location 2 (Figure 6). The tubes were installed by a modified
tractor-mounted press that punched a 2.22-cm diameter hole. The soil-water
extraction tubes were made of 1.27-cm diameter schedule 80 polyvinyl
chloride (PVC) pipe with a porous ceramic tip. A 0.32-cm O.D. nylon line
was glued into the ceramic bulb and was inside the PVC pipe. The line
connected the bulbs to a water sample collection bottle and a vacuum mani-
fold. The vacuum manifolds were installed alongside the water extraction
tubes. They were constructed from 1.91-cm PR-200 PVC line with holes
drilled to fit a No. 00 rubber stopper. When an extraction was completed at
a particular depth, the extraction tube was disconnected from the manifold.
The only serious problem that occurred was the evaporation of water from the
collection bottles. This was eliminated by adding mineral oil to the
bottles.
Soil-Water Potential Measuring System--
Tens iometers (Model R, Irrometer Company, Riverside, California) were
used to measure soil-water potential. Figures 5 and 6 show the number of
tensiometers and depths of each for both locations in each plot. Tensi-
ometers were installed by the same method used for installation of soil-water
extraction tubes. The only problem encountered with this type of tensi-
ometer was that the rubber stopper occasionally stuck to the main body and
twisted off when the cap was unscrewed for servicing. The shallow depth
tensiometers were serviced approximately once a week (after each irrigation)
and the others approximately every two weeks.
Soil-Water Content Measuring System-
Soil -water content was measured with neutron probes inserted into
permanently installed access tubes. Each plot had two neutron probe access
tubes installed to a depth of 9.14 m, one at each soil instrumentation
location as shown in Figures 5 and 6. These tubes were 5.08-cm diameter
aluminum, installed in 5.08-cm diameter holes drilled with a modified
trailer-mounted rig. Soil moisture content was monitored with two neutron
moisture meters and probes (Model 2651 Scaler-Ratemeter and Model 104A
Depth Moisture probes, Troxler Electronic Laboratories, Inc., Research
Triangle Park, North Carolina).
It was necessary to construct standards to calibrate the neutron
probes. Three soil textures were used to make standards for the purpose
of calibrating neutron moisture probes. The soil textures used were: loam
(42% sand, 23.3% clay), sandy loam (60% sand, 19.6% clay), and sandy loam
(76% sand, 11.3% clay). The soil was obtained from different field sites
and air-dried.
Containers used for the standards were 208-1 oil drums. Volume was
marked on the inside of the oil drums. The air-dried soil was weighed in
lots equal to the desired bulk density and mixed with water in a cement
16
-------
3.05 Q-r Q TENSIOMETER
0.46 D
2.74 O-L
2.43 O
2.13 O
«-•'*' \ /
1.83 O
1.52O
9.14 (3)
1.22 O
0.91 O
0.61 O
0.46 O
0.30 O
0.15 O
n
O
V
0.150
0.46 0
0.91®
1.520
2-130
2.740
4.570
7.620
yj iUlL WAItK
EXTRACTION
g) NEUTRON PROBE
0.30 0-r
0.61
0.61 01
1.22 Q
1.83 0
2.43 0
3.05 Q
6.10 0
9.14 (D
TUBE
Figure 5. Soil instrumentation layout in Location 1 in each plot
of the field site near Munday, Texas. Depth of each
instrument is as indicated. (Depths and dimensions
in meters.)
17
-------
1.520
0.61
1.220
0.61
1.22 O
0.91
0
0.91
O
0.61 0
0.61
0.460
9.14
D
1.300
0.150
0.46 O
0.30
0.15
O TENS IOMETER
0 SOIL WATER EXTRACTION TUBE
® NEUTRON PROBE ACCESS TUBE
Figure 6. Soil instrumentation layout at Location 2 in each plot of
the field site near Munday, Texas. Depth of each instru-
ment is as indicated. (Depths and dimensions in meters.)
18
-------
mixer to obtain the desired moisture content. After each lot was thoroughly
mixed, it was dumped and covered until all lots were mixed. All lots were
then mixed together to assure a homogeneous moisture content. The soil was
then weighed out at its wet density in 0.28-hectoliters (hi) batches and
packed in the container around the access tube. A piece of 0.64-cm plywood
covered with black plastic asphalt cement was used to seal each container.
Sixteen standards were made with varying moisture contents and bulk
densities.
After a few neutron moisture content readings were made, it was
determined that a layering effect existed due to moisture content. A soil
core was taken from each container to determine the moisture content of
each layer.
Bulk density was found to affect the moisture content values as deter-
mined by the neutron probe. It was necessary to determine the bulk density
of each hole at the site and develop equations for each neutron probe that
were based on bulk density as well as the moisture content standards. This
was accomplished by use of a density probe (Model 2651, Troxler Electronic
Laboratories, Inc., Research Triangle Park, North Carolina).
System for Measuring Climatic Conditions--
Figure 1 shows the layout of the meteorological instrumentation. This
instrumentation consisted of the following:
(1) Hygrothermograph, Model 594, Bendix Corporation, Environmental
Science Division, Baltimore, Maryland
(2) Rain and Snow Gauge, Model 775C, Bendix Corporation, Environ-
mental Science Division, Baltimore, Maryland
(3) Microbarograph, Friez Model 790-1, Bendix Corporation,
Environmental Science Division, Baltimore, Maryland
(4) Aerovane Wind Transmitter, Model 120, Bendix Corporation,
Environmental Science Division, Baltimore, Maryland
Aerovane Recorder, Model 141, Bendix Corporation, Environ-
mental Science Division, Baltimore, Maryland
Aerovane Support, Model 150, Bendix Corporation, Environ-
mental Science Division, Baltimore, Maryland
(5) Solar Radiation Recorder, Model R-401, Weather Measure
Corporation, Sacramento, California
(6) Evaporation Pan, Catalog No. 242, Science Associates,
Princeton, New Jersey
(7) Totalizing Anemometer, Catalog No. 404, Science Associates,
Princeton, New Jersey
19
-------
(8) Volt Time Integrator, Catalog No. 618-1, Science Associates,
Princeton, New Jersey
(9) Pyreheliometer, Catalog No. 636, Science Associates, Princeton,
New Jersey
Electrical Power System—
The location of the buried 440 volt electrical cable is as shown in
Figure 1. Another buried cable furnished 110 and 220 volts to the field
office. At each well and at two power poles in the field the 440 volts were
transformed to 110 volts for small electric motor use, such as those on the
vacuum pumps.
Irrigation System—
The irrigation system (Figure 1) consisted of the two irrigation wells,
an underground pipeline that connected the two wells, and the three types of
irrigation systems - sprinkler, furrow, and manual subirrigation.
Irrigation wells and pipelines--The two irrigation wells were 17.4 m
deep with a 11.2-kilowatt (kw) submersible pump set in each well. The
pumping capacity of each well was approximately 927 1pm. At this rate, very
little sand was pumped. A flow meter was located at each well, and the dis-
charge passed through a sandtrap before entering the underground mainline.
The underground pipeline was 15.24-cm diameter PVC. All components of the
mainline pipe above the ground were steel.
Sprinkler irrigation system—The sprinkler irrigation system was solid
set in a triangular pattern with sprinklers located 12.2 m apart along the
laterals. The laterals were 5.08-cm diameter aluminum with 1.91-cm diameter
galvanized steel risers 1.83-m tall. The sprinklers had 0.44-cm diameter
brass nozzles. The flow was limited to each lateral by a 113-lpm flow
control valve. With this flow, each sprinkler discharged 18.9 1pm at 2.8
bar lateral pressure.
Furrow irrigation system—The furrow plots were leveled for even
distribution of water through 15.24-cm diameter gated slip-joint aluminum
irrigation pipe. Gates were 5.08-cm diameter butterfly valves spaced 102 cm
apart. The amount of water delivered to each plot was metered through a
15.24-cm magnetic-drive flow meter.
Manual subirrigation system—The subirrigation laterals were installed
with a modified chisel at an approximate depth of 45 cm below the soil
surface. There was a lateral under each row (rows on 102-cm centers).
These laterals were made of 1.27-cm diameter polyethylene pipe with 0.06-cm
diameter Whitney-type subirrigation orifices spaced 0.91 m apart. The
laterals were connected to 5.08-cm PVC header lines on each end of the plot
which were also beneath the soil surface.
Following filterings, the water entered headers on each end of the
plot. The flow to each header line was controlled by a 56.7-lpm flow
control valve. Thus, the total flow to each plot was limited to 113 1pm.
Filter cartridges (350 micron) were used in the filtering system.
20
-------
Automated sub-irrigation system—A 5.08-cm PVC mainline was installed
from the pressure tank at the east well to furnish water for these plots.
The pump that furnished water for the pressure tank pumped approximately
95 1pm. The pressure switch on the tank was set at a 2.8 to 4.1 bar
pressure range. A 113-lpm filter was installed in the mainline to filter
the water. Filter cartridges (100 micron) were used.
Six plots (Figure 1) were installed for the automated subirrigation
system with dimensions of 16 102-cm rows wide and 67 m long. Polyethylene
laterals, 1.27-cm diameter, with insert orifices spaced every 0.91 m were
installed on 102-cm centers at a 25- to 30-cm depth with a chisel plow. PVC
header lines, 5.08-cm diameter, were installed at each end of the plots to
insure uniform water distribution. The laterals were connected to the
header line with 1.59-cm O.D. Tygon tubing by drilling a 1.43-cm hole in
the header pipe and inserting the Tygon tubing into the hole. The other
end of the Tygon tubing was slipped into the lateral and clamped.
The control valves for each plot consisted of a 120 VAC normally closed
solenoid valve (Valve No. 21106021, Hays Manufacturing Company, Erie,
Pennsylvania), a 37.8-lpm flow control valve for each header pipe, and
necessary gate valves for flushing.
An automated trickle-irrigated plot was also installed with the auto-
mated subirrigation plots. It was six 102-cm rows wide and 67 m long. The
laterals were the same as used for the subirrigation system. They were
connected to a 1.91-cm PVC header line with slip-joint connectors and
plugged on the other end. The amount of water delivered to the plot was
controlled by a 56.8-lpm flow control valve. Controls for the plots are
described in a publication by Wendt, et al. (23).
Hodels
Hydraulic Conductivity--
One of the major parameters affecting water and ion movement is the
hydraulic conductivity of the soil profile. The method used to determine
hydraulic conductivity was that of Mil lei, et al. (9) which is described by
the following equation
K = (dW/dt)Z/(3H/3Z)Z [1]
where K = hydraulic conductivity
(dW/dt)Z = change in water content with time at depth Z
(3H/9Z)Z = hydraulic gradient at depth Z.
As will be discussed later, the soil texture varied considerably below
the soil surface. It was necessary to select sites with the range of soil
textures to obtain the necessary range of hydraulic conductivities. Three
sites with a range of soil textures between 0 and 3 m were located for the
hydraulic conductivity study. Plots 6 x 6 m were used in the study. Tensi-
ometers and neutron probe access tubes were installed in triplicate near
the center of each plot (Figure 7). Tensiometers were installed at random
to a depth of 3 m and access tubes were installed to 3.7 m. Soil samples
21
-------
4.0 m
3.7 m
0.3 m
k 4
2.1 m
2.1 m
3.7 m
TENSIOMETERS
NEUTRON ACCESS
TUBES
Figure 7. Plot design used in hydraulic conductivity studies in Knox
County, Texas. (Tensiometers spaced at 0.3-m intervals at
random depths to 3.0 m around each access tube. Neutron
access tubes spaced 2.1 m apart in an equilateral triangle
to 3.7-m depth.)
for textural analysis were obtained at 0.30-m intervals at the time the
neutron probe access tubes were installed. Bulk densities at 0.30-m inter-
vals were determined for each hole using a calibrated bulk density probe.
Water Balance--
The total water balance of the root zone has been presented by Hi 11 el
(8) as follows
where
AW = M + Ir - N - F - (E + T)
[2]
AW = change in root-zone water content
M = precipitation
Ir = irrigation water applied
N = runoff
F = deep percolation
E + T = evaporation + transpiration or evapotranspiration (ET).
22
-------
Precipitation and irrigation water applied can be easily measured.
Runoff can be prevented or measured. Deep percolation and ET losses can be
determined by quantitative measurements of soil -water content.
One method of assuring that a minimum amount of water is available for
deep percolation is to apply only that necessary for ET. One commonly used
approach is to evaluate some method for estimating ET. The model evaluated
in this study is that of Penmann, further developed by Jensen, et al . (10).
The Jensen model, commonly used in the western United States, is
O - G + j-jL- (15.36) (1.0 + 0.01W) es - ed [3]
where E* = evaporative flux (latent heat)
A = slope of the saturation vapor pressure-temperature
curve (de/dT)
Y = psychrometric constant
e = mean saturation vapor pressure (mean at maximum and
minimum daily air temperature)
e , = saturation vapor pressure at mean dew point temperature
W = total daily wind run
R = daily net radiation
G = daily soil heat flux.
Where day-to-day temperatures do not change greatly and day-to-day
radiation is similar, soil heat flux (G) is relatively small during the
summer months and can be neglected.
Net radiation values are necessary for the above model. Such measure-
ments are difficult to obtain and not readily available. However, proce-
dures have been developed for estimating net radiation using observed solar
radiation for a day. Cloudless day values can be obtained from estimates
by Fritz (5) or by plotting clear day values to obtain an envelop curve
through the high points as follows
Rn = (1 - a)Rs - Rb [4]
where a = albedo
R = observed daily solar radiation
R. = net outgoing long wave radiation
R, can be estimated as follows
Rb = (aRs/Rso + b)Rbo [5]
where R = solar radiation on a cloudless day
so
R. = net outgoing long wave radiation on a clear day
bo which was estimated as follows
23
-------
T2 + Tl
Rbo = [0.98 - (0.66 + 0.044/ed)] (11.71 x 10"8) —^ [6]
where e, = saturation vapor pressure at mean dew point
o temperature
11.71 x 10 = Stefan-Boltzmann constant
T2. and Tl. = maximum and minimum daily air temperatures.
A plant factor is necessary to fully utilize the ET potential model of
Jensen (10) since the ET of a system with small plants is less than a
system with large plants and is not equal to the potential ET. Ritchie (21)
has shown that the ET of a crop is related to the leaf area of the crop.
Equations were developed to determine leaf area using stem diameter to
evaluate the Jensen model. The generalized equations used were
Log Y = a + b Log X [7]
/y = a + b /x"
where y = leaf area
x = stem diameter 2.54 cm above the ground.
Stem diameter measurements were made every two weeks on 10 plants in
11 plots.
Treatments
Portions of the field site were not suited for furrow irrigation
because of the undulating topography. The most level land was near the
center of the site. Therefore, plots were grouped by method of irrigation
and, to facilitate irrigation, by moisture level. Irrigation, fertilizer
treatments and treatment arrangements for the four years are listed in
Table 1.
To simplify field operations, plots were numbered from east to west
(Figure 1). Plots 1 through 13 were sprinkler-irrigated, Plots 14 through
26 were furrow-irrigated, and Plots 27 through 39 were subirrigated. For
ease of reference, plot numbers and fertilizer treatments are listed in
Table 1. The north half of each plot was designated as Location 1, and
the south half as Location 2.
Plots in the Ml moisture treatment were irrigated when the upper leaves
of the corn began to curl at midday. Plots in the M2 moisture treatment
were irrigated when the soil-water potential at the 15-cm depth declined to
-20 or -30 cb. Plots in the M3 moisture treatment were irrigated when the
soil-water potential at the 15-cm depth declined to -40 or -60 cb. The -30
and -60 cb potentials were used during the first year (1971) for the respec-
tive levels. However, severe stress developed during critical stages of
growth on the -60 cb plots, and the levels were changed to -20 and -40 cb
levels, respectively, for the remaining years. The automated subirrigation
plots had switching tensiometers set at 30 cm which activated the systems
24
-------
TABLE 1. FERTILIZER AND IRRIGATION TREATMENTS FOR THE 1971-1974 CROP YEARS AT THE KNOX COUNTY,
TEXAS, FIELD SITE
Plot
no.
1
2
3
4
5
6
7
8
9
10
n
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
23
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
YEAR
1971
M3
M3
H3
M3
M3
M2
M2
M2
M2
M2
Ml
Ml
Ml
M3
M3
M3
M3
M2
M2
M2
M2
Ml
Ml
Ml
Ml
Ml
M3
M3
M3
M3
M3
M2
M2
M2
M2
M2
Ml
Ml
Ml
FIT
F6
F6
F4
F2
F11
F6
F6
F4
F2
Fll
F6
Fl
Fll
F6
F4
F2
Fll
F6
F4
F2
Fll
F6
F6
Fl
Fl
Fll
F6
F6
F4
F2
Fll
F6
F6
F4
F2
FIT
F6
Fl
A3
A2
A2
A2
A3
A2
A2
A2
A2
A2
A3
A2
A2
A3
A2
A2
A2
Al
A2
Al
A3
A2
A2
A2
A3
A2
A2
A2
A2
Al
1972
M3 Fll
M3 F6
M3 F6
M3 F4
M2 Fl
M2 Fll
M2 F6
M2 F6
M2 F4
M2 F8
Ml Fll
Ml F6
Ml Fl
M3 FIT
M3 F6
M3 F4
M2 Fl
M2 FIT
M2 F6
M2 F4
M2 F8
Ml Fll
Ml F6
Ml F6
Ml Fl
Ml Fl
M3 Fll
M3 F6
M3 F6
M3 F4
M2 Fl
M2 Fll
M2 F6
M2 F6
M2 F4
M2 F8
Ml Fll
Ml F6
Ml Fl
M4 F6
M4 F6
M4 Fll
M5 F6
M5 F6
M5 Fll
A3
A2
A2
A2
A3
A2
A2
A2
A2
A2
A3
A2
A2
A3
A2
A2
A2
Al
A2
Al
A3
A2
A2
A2
A3
A2
A2
A2
A2
A2
A2
A2
A2
A3
1973
M3 FIT
M3 F6
M3 F6
M3 F4
M3 Fl
M2 F9
M2 F7
M2 F7
M2 F5
M2 Fl
M2 Fll
Ml F6
Ml Fl
M3 Fll
M3 F6
M3 F4
M3 Fl
M2 F9
M2 F7
M2 F5
M2 Fl
M2 Fll
Ml F7
Ml F7
Ml Fl
Ml Fl
M3 FIT
M3 F6
M3 F6
M3 F4
M3 Fl
M2 F9
M2 F7
M2 F7
M2 F5
M2 Fl
M2 Fll
Ml F6
Ml Fl
M4 F7
M4 F7
M4 Fll
M5 F6
M5 F6
M5 Fll
1974
A2
A2
A2
A2
A3
A2
A2
A2
A2
A2
A3
A2
A2
A2
A3
A2
A2
A2
Al
A2
Al
A3
A2
A2
A2
A3
A2
A2
A2
A2
A2
A2
A3
A2
A3
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M2
M4
M4
M4
M5
MS
MS
F10
F6
F6
F4
Fll
F7
F3
F10
F6
F4
Fll
F6
F6
F3
F3
F10
F6
F6
F3
FIT
F7
F3
F6
F6
Fll
F6
F6
Fll
A2
A3
A2
A2
A2
A2
A2
A3
A2
A2
Al
A2
•A2
A2
A3
A2
A2
A2
A2
A2
A3
A2
A3
Legend for irrigation and fertility treatments
Irrigation system:
Plots 1 - 13 - Sprinkler
14-26 - Furrow
27 - 39 Manual Subirrigation
40-45 - Automated Subirrigation
46 - Automated Trickle Irrigation
Moisture level :
Ml - High Moisture level based on growth (sig-
nificant upper leaf curl at midday)
M2 - High Moisture level based on potential at
15.24 cm, -30 cb in 1971, -20 cb in 1972,
1973, 1974
M3 - Moderate Moisture level based on potential
at 15.24 cm, -60 cb in 1971, -40 cb in 1972,
1973, 1974
M4 - Constant High Moisture level based on poten-
tial at 30.48 cm, -20 cb
M5 Constant Moderate Moisture level based on
potential -40 cb
Fertilizer sources:
Fl - Anhydrous Ammonia
F2 - Anhydrous Ammonia + N-Serve
F3 - Anhydrous Ammonia + Sodium Bromide
F4 - Sulfur Coated Urea
F5 - Sulfur Coated Urea + Sodium Bromide
F6 - Nitrogen Solution
F7 - Nitrogen Solution + Sodium Bromide
F8 - Sodium Nitrate + Sodium Bromide ,r
F9 - Sodium Nitrate + two small plots of N-
enriched Sodium Nitrate + Sodium Bromide
F10- Sodium Nitrate + 1/2 of two small plots
in F9 fertilized with '->N-enriched Sodium
Nitrate
Fll- Control
Method of fertilizer application:
Al - Chiseled Below Bottom of Water Furrow
A2 - Chiseled Above Bottom of Water Furrow
A3 - Applied in Irrigation Water
46
M4 F6 A3 M4 F7 A3 M4 F6 A3
25
-------
when soil-water potentials reached -20 and -40 cb for the M4 and M5
treatments. In general, the potentials dropped to -10 and -30 cb in the
M4 and M5 levels following moisture additions due to a lag in the movement
of the applied water to the tensiometers. However, since water was not
lost from the root zone, the lag was not considered significant.
Initially, fertilizer materials used in 1971 were chosen because of
the following potential advantages. Anhydrous ammonia containing 82% nitro-
gen is commonly used and costs less. "N-Serve" contains a bacteria inhib-
itor which slows the rate of nitrification and thus should reduce the amount
of leachable nitrate present in the soil at any particular time. The sulfur
coating around urea is gradually desolved and decomposed by soil organisms
and thus should gradually release nitrogen as it is needed by plants.
Nitrogen solutions are easily applied with irrigation water and thus facil-
itate "spoon-feeding" of the crop.
Plots to which the N-Serve was added to anhydrous ammonia did not show
a yield advantage during the 1971 growing season, and the plots that
received this treatment were either fertilized with anhydrous ammonia
(Plots 15, 17, 30) or sodium nitrate (Plots 10, 21, 36) in 1972 (Table 1).
Sodium nitrate was used as a nitrate-N source. Sodium bromide was
applied with the sodium nitrate to determine the usefulness of bromide as a
tracer for fertilizer nitrate in soils.
In 1973, Plots 5, 17 and 31 were returned to the M3 or moderate mois-
ture level since Plots 10, 21 and 36 were fertilized with anhydrous ammonia.
Plots 6, 18 and 32, previous control plots for the M2 moisture level, were
used for the 15N tracer study. The 15N-enriched fertilizer as sodium
nitrate and sodium bromide was applied to two 6 x 6 m subplots within each
of the main plots. The enriched fertilizer and sodium bromide were applied
in a water solution through a chisel for more precise application. The
subplots were located adjacent to the existing instrumentation locations
and sampled with a high clearance soil coring rig specifically designed for
the study (1). Plots 11, 22 and 37 were used as control plots for both the
Ml and M2 moisture levels since both were high moisture level treatments.
In addition to these changes, sodium bromide was applied to Plots 7, 8,
9, 19, 20, 23, 24, 33, 34, 40 and 41 and a trickle plot to determine the
movement of fertilizer nitrates by the various irrigation methods. The
bromide was applied to six rows (two rows on either side of the two rows
containing the soil-water sampling tubes).
Not all plots were utilized in 1974 since the only additional informa-
tion needed to complete the objectives of the project were on the fate of
15N and movement of fertilizers below the root zone. Plots 1-5, 10, 14-17,
21 and 27-31 were not included in the study in 1974. Sodium bromide was
applied as a tracer to those plots that received excess water (Plots 12, 13,
25, 26, 38, 39).
In 1974, 15N-enriched sodium nitrate was applied to one-half (3 x 6 m)
of the original 6 x 6 m plot fertilized with 15N in 1973. The other half of
the plot was fertilized with an equal rate of unenriched sodium nitrate.
26
-------
Enrichment levels of 15N were 6.2 atom percent in 1973, 7.0 atom percent at-
the planting application in 1974, and 6.4 atom percent for the sidedress
application in 1974.
Laboratory Facilities and Procedures
A laboratory was established at the Texas ASM University Vegetable
Research Station at Munday to make the necessary analyses on soil, water
and plant samples from the field site. Chemical analyses were determined
by an AutoAnalyzer (Model CSM-6, Technicon Industrial Systems, Tarrytown,
New York) which operates as follows: A sample stream from an automatic
sampling device is divided into seven individual streams for analysis.
Each stream passes through one of two proportioning pumps which meter
sample, reagent, and air bubbles to segment the streams. The sample stream
may also be automatically diluted with distilled water if high concentra-
tions are expected. Six of the streams pass through mixing coils for
reaction and color development. After reaction, streams are fed to sample
flowcells in the colorimeter where they are debubbled and colorimetrically
analyzed using a common light source and appropriate filters. Phototubes
furnish input signals for a signal conditioner, where the signals are ampli-
fied and recorded on a continuous recording strip chart recorder. The
seventh stream is aspirated into a dual channel flame photometer.
The AutoAnalyzer was programmed to make the analyses by the following
methods:
Nitrate and Nitrite--
Nitrate was reduced to nitrite by a copper-cadmium reductor column.
The nitrite ion reacted with sulfanilamide under acidic conditions to form
a diazo compound. This compound coupled with N-Napthylethylenediamine to
form a reddish-purple Azo dye. The final product measured represented the
nitrite ion originally present plus that formed from the nitrate. Original
nitrite was simultaneously determined on a separate channel without the
reductor column. Nitrate concentration was then determined by subtraction.
Chloride--
The automated procedure for the determination of chloride depends on
the liberation of thiocyanate ion from mercuric thiocyanate by the formation
of un-ionized but soluble mercuric chloride. In the presence of ferric ion,
the liberated thiocyanate forms highly colored ferric thiocyanate, in
concentration proportional to the original chloride concentration.
Ammonium--
The procedure for determining ammonium utilizes the Berthelot Reaction
in which the formation of a blue-colored compound believed to be closely
related to indophenol occurs when the solution of an ammonium salt is added
to sodium phenoxide followed by the addition of sodium hypochlorite. A
solution of potassium sodium tartrate (Rochelle Salts) is added to the
sample stream to eliminate the precipitation of the hydroxides of heavy
metals which may be present.
27
-------
Orthophosphate--
Orthophosphate was determined by the well-known method whereby ammonium
molybdate reacts in an acid medium to form molybdophosphoric acid which is
then reduced to the molybdenum blue complex by reaction with ascorbic acid.
Sulfate—
Sulfate was determined by a turbidimetric analysis procedure. The
sample or distilled water wash was continuously aspirated into the analyt-
ical system. A three-way solenoid valve was used to add sequentially
barium chloride and a sodium salt of ethylenediamine tetraacetic acid
(EDTA) to the sample at precise time intervals. The sequential introduction
of the sodium salt of EDTA during the wash cycle prevented the accumulation
of barium sulfate on the flow cell walls, thus preventing base line drift
on the recorder. Barium chloride reagent reacted with sulfate in the sample
to form an insoluble barium sulfate suspension. The barium chloride reagent
was acidified to prevent precipitation of carbonate, chromate, phosphate,
and oxalate of barium. Gelatin was used to hold the barium sulfate in
suspension.
Calcium, Potassium and Sodium--
Calcium, potassium and sodium were determined by flame emission using a
dual channel flame photometer with lithium as an internal standard. As the
flame photometer was limited to only two channels in 1971, it was necessary
to pass all samples through the AutoAnalyzer again for determination of the
third cation.
In order to minimize manual dilutions of samples, the AutoAnalyzer was
calibrated to operate in the following ranges:
Nitrate + Nitrite 0 - 100 ppm
Nitrite 0 - 5 ppm
Chloride 0 - 300 ppm
Ammonium 0 - 10 ppm
Orthophosphate 0 - 10 ppm
Sulfate 0 - 500 ppm
Calcium 0 - 300 ppm
Sodium 0 - 300 ppm
Potassium 0-100 ppm
Standard curves were recorded preceding and following each series of 95
samples. Concentrations of unknowns were determined from chart readings by
deriving the equations of the standard curves with a programmable computer
and substituting values.
Total salt concentration of each sample was determined through EC made
with a conductivity bridge (Model RC 16B2, Beckman Scientific Process
Instruments Division, Fullerton, California).
Few 1971 soil-water extract samples had contained more than 0.1-ppm
nitrite or 5-ppm phosphate and both analyses were discontinued in succeed-
ing seasons. Colorimetric analyses for calcium and magnesium were substi-
tuted for nitrite and phosphate on the AutoAnalyzer so that analyses for all
28
-------
eight ions could be completed in one run. Calcium was determined via its
reaction with glyoxyl-2-hydroxayanil reagent. Iron is complexed with
triethanolamine (TEA), a buffer is added to control pH, and a red color
results when potassium cyanide (KCN) and 2,2-(ethanediylidenedinitrilo-
diphenol) are added. The determination of magnesium is based on the
development of a blue complex between magnesium hydroxide (MgOH2) and
magnesium blue. Magnesium hydroxide is precipitated in an alkaline solu-
tion, and magnesium blue dye is absorbed in the presence of a wetting agent
in a suspending material, polyvinyl alcohol (PVA). A compensating reagent
is added to mask possible interferences. Iron is complexed with TEA.
Calcium is complexed with ethyleneglycol bis(aminoethylether) tetraacetic
acid (EGTA), and silica is complexed with sodium fluoride (NaF).
Bromide was used as an indicator in the study of sampling technique
efficiency. Analyses of bromide in soil-water extracts and extracts from
soil samples were made with a bromide electrode (Model 94-35, Orion
Research Inc., Cambridge, Massachusetts). The electrode sensing element
is a silver halide/silver sulfide membrane, which is an ionic conductor for
silver. The potential developed within the electrode is fixed, so that the
electrode develops potentials due only to changes in the sample silver ion
activity., Even though the original sample may not contain silver ions, a
very few are produced by the extremely small solubility of the silver halide
membrane. The silver ion activity depends on the halide ion activity in the
sample solution. Although there was interference between bromide and
chloride, it was possible to compensate for the interferences by solving
equations which describe the interferences (18).
Some changes were also made in laboratory procedures in 1973 to process
samples for 15N/1[tN isotope-ratio analyses. Soil samples were air-dried,
ground with a hammer mill, and extracted with equal amounts (weight/volume)
of 2N sodium sulfate. The soil solutions were centrifuged to remove
suspended soil and analyzed for nitrate and ammonium with the AutoAnalyzer.
A Kjeldahl digestion-distillation unit (Catalog No. S-63215, Sargent-
Welch Scientific Company, Dallas, Texas) was used in the 15N study.
Extracts of samples selected for isotope-ratio analysis were treated with
magnesium oxide and ammonium was distilled. De'Varda's alloy was then added
to convert nitrate to ammonium and ammonium (of nitrate source) was dis-
tilled into a separate receiver. The ammonium fractions were concentrated
and transferred to small vials for isotope-ratio analyses at another
laboratory.
Total nitrogen analyses were performed on most soil samples from
15N-treated plots. Soil samples were treated with potassium permanganate,
reduced iron, and sulfuric acid to convert nitrate to ammonium. The
organic fraction was subsequently converted to ammonium by boiling the
sample in sulfuric acid and a mixture of copper sulfate, potassium sulfate,
and selenium. After digestion was complete, sodium hydroxide was added,
and ammonium was distilled and concentrated for isotope-ratio analysis.
Procedures used for the 15N analyses were those presented by Bremner
(3). A mass spectrometer (Model 21-104, Consolidated Electrodynamics Corp.,
29
-------
Pasadena, California), located at the Trace Analysis Institute, Texas A&M
University, College Station, Texas, was used for the isotope-ratio analyses
in 1973 while a mass spectrometer (Model 21-620, Consolidated Electrody-
namics Corp., Pasadena, California), located at the Chemistry Department,
Texas Tech University, Lubbock, Texas, was used to analyze the samples
obtained in 1974.
LUBBOCK LOCATION
A prototype of the proposed automated subirrigation system for the
Munday site was installed at the Texas A&M University Agricultural Research
and Extension Center at Lubbock during May and June of 1971. The system was
evaluated and modifications were made during the growing season of 1971.
The field layout consisted of two plots (Figure 8). Each plot was 16 102-cm
rows wide and 67 m long. The 67-m laterals were centered on 102-cm bedded
rows and chiseled to a depth of 30 cm. The laterals were 1.27-cm diameter
polyethylene plastic pipe with nylon insert orifices (Figure 9) every 0.91 m
along the laterals. The main and header pipes consisted of 5.08-cm PVC
pipe. The 5.08-cm main pipe was designed to deliver well water to each of
the header pipes within each plot. A header pipe was installed on opposite
ends of 67-m laterals to reduce the pressure drop within the laterals. Two
1.27-cm, 9.46-lpm flow control valves and one 1.91-cm 120V/10amp normally
closed solenoid controlled both the flow and flow rate into each set.
Controls for opening the solenoid have been described in a publication
by Wendt, et al. (23).
30
-------
Plot A
Plot B
1.91-cm PVC Header7
Normally Closed
Solenoid Valve
1.27-cm
Polyethylene
Laterals
4
9.46-lpm Valve
100 y Filter
5.08-cm PVC Main
Figure 8. Subirrigation system layout at the field site at Lubbock,
Texas. Each plot is 16 rows wide (102-cm centers) by 67 m
long.
31
-------
WHITNEY ORIFICE
0.056 cm
1.27 cm
POLYETHYLENE PIPE
Figure 9. Schematic of orifice inserted in plastic
pipe in subirrigation systems at Munday,
and Lubbock, Texas.
32
-------
SECTION 5
EXPERIMENTAL PHASE
MUNDAY LOCATION
Many endeavors related to this project were necessary to all objectives,
It is the purpose of this section to summarize this information so that the
objectives can be discussed without duplication of information. Further, a
voluminous amount of data were obtained during the four years of the project.
Only data most pertinent to the objectives will be included in this report.
Appendices of all data are available and may be obtained by contacting
either the authors or the U. S. Environmental Protection Agency. Activities
which were necessary for all objectives were the recording of cultural
information and measurement of climatic, plant and soil parameters. A
discussion of each of these activities follows.
Cultural Information
Pertinent Information on Planting, Pesticide Applications and Harvesting--
Pertinent information on planting, pesticide applications, and harvest-
ing is presented in Table 2. Some problems occurred in planting during the
first two years of the study. During the first year, the initial planting
in the furrow resulted in a low plant population, and the crop was replanted
on the bed. There was some problem in obtaining emergence on the subirri-
gated plots when they were planted on the bed. It was necessary to apply up
to 20 cm of water to obtain emergence. Plots 27, 28, 32, and 33 were
replanted on July 2 in the furrow to see if it would be possible to obtain
good emergence without the use of large quantities of water on subirrigated
plots. A good stand was obtained when only 0 to 5 cm of water were applied
through the subirrigation system. Furrow planting over the subirrigation
lateral will apparently be necessary in these porous soils to obtain emer-
gence with the current placement of the laterals of 30 to 36 cm below the
soil surface.
Two lots of seed were planted in the 1971 study. One lot was appar-
ently a second generation hybrid, while the other lot was of excellent
quality seed. However, the majority of the plots had poor quality seed.
This was not discovered until the plants had begun to grow and silk. Many
sterile stalks existed among the plots which affected yield.
Poor growth occurred during 1972. An examination of the plants showed
that the root system was so poorly developed that it did not grow to the
banded fertilizers. A starter band of fertilizer was applied 8 x 8 cm from
33
-------
TABLE 2. PERTINENT PLANTING, PESTICIDE APPLICATIONS, AND HARVESTING INFORMATION, 1971-1974
U)
45.
Variety
Planting date
Rate (kg/ha)
Replanting date
Rate (kg/ha)
Insecticide &
application
dates
(Mfgs. recom-
mended applica-
tion rate used)
Herbicide
Application dates
(Mfgs. recom-
mended applica-
tion rate used)
Harvest date
1971
2nd crop
Plots 22,
1st crop 28, 32,
(all plots) 33
Sweet Tex 2
June 8-10 July 21
24.6 24.6
June 18-19
24.6
Sevin on July 27,
Aug. 19 & 27,
Parathion on
July 30, Sevin
on Sept. 10
Atrazine Atrazine
July 12 Aug. 4
Sept. 10 Sept. 30
1972
1st crop
(all plots)
2nd crop
Plots 6-8,
17-19, 32-34,
40-45
Bonanza
April 13-14
16.8
Plot 46 May 17
16.8
Sevin + Zinc
Sulfate,
June 19
Atrazine
April 28
Plots 1-45
July 6-7
Plot 46
July 28
Aug. 2
16.8
Sevin,
Aug. 15
Sevin + Di-
azinon
Ag 500,
Aug. 24 &
29, Sept.
12 & 20
Atrazine
Aug. 2
Oct. 11
1973 1974
(all plots) (all plots)
Bonanza NK Exp 435
May 2-4 April 23-24
16.8
Plots 30-34
Diazinon AG
500.
All plots Diazi-
non AG 500
June 20 & 27
Dylox July 6
Atrazine Atrazine
May 24-25 May 8
July 16-18 July 8-9
-------
the seed at planting in 1973 and 1974 to assure vigorous growth immediately
following emergence. Apparently adequate fertility existed on the site to
establish the crop during the first year because the area had not been
irrigated. The fertility was low during the following years due to heavy
cropping; therefore, nitrogen at a rate of approximately 25 kg/ha was neces-
sary for crop establishment. This was the only fertilizer applied to control
plots.
Since sweet corn is a short season crop, it can be planted over a five-
month period in the area, it was planted on dates between April 13 and
August 2 during the four years of the study. The first year (1971) of the
study, it was planted in June since much time was involved in establishing
the field site. A July planting was made to see if the amount of water
required to establish corn over subirrigation systems could be decreased.
Two plantings were also made in 1972 to obtain further information on the
newly installed subirrigation systems and to determine if the poor growth
on the first crop could be circumvented through fertilization.
Insecticide applications varied from none (1974) to five in 1971 and
1972. In general, the later the crop was planted, the more insecticide
applications were required. The crop was besieged at various times during
the four years with fall armyworms, southwestern corn stalk borers, corn
ear worms, and webworms. In some of the late plantings, the corn borers
entered the plants almost as soon as they emerged, and insect control was
minimal from some of the insecticide applications. It thus appears that
the production of sweet corn in the area will be feasible only if it is
planted early (March or April).
Excellent weed control was obtained through the use of 1.7 to 2.2 kg
of Atrazine per ha each year in a post-emergence application.
Harvest dates ranged from July 8 to October 11, depending on when the
crop was planted. Yield data taken for most harvests were ear number/ha,
length, weight, and diameter. Only yield/ha was determined on the
October 11, 1972, harvest. Yield data in the form of weight of ears/ha
and number of ears/ha will be discussed in this report.
Fertilization--
Sources, rates, and application dates of various fertilizers used in
the study during the four years are shown in Table 3. Methods of applica-
tion have previously been noted in Table 1. All fertilizer was applied
either with chisels set on 50.8-cm centers or through the irrigation
systems. With the chisels on 50.8-cm centers, the fertilizer was'placed
25.4 cm to the side of the plants and either 10.2 cm (above the water
furrow) or 20.3 cm (below the water furrow) deep. Initially, fertilizer
was injected into irrigation water with positive displacement pumps (Ameri-
can Meter Model Nos. 150721 and 150722, Raguse and Company, Inc., 3726
Peoria, Tulsa, Oklahoma). In later installations, a venturi injector
(Model 202, Dema Engineering Company, 10020 Big Bend Boulevard, St. Louis,
Missouri) was substituted for the pump.
35
-------
TABLE 3. FERTILIZER SOURCES*, RATES (KG/HA) AND DATES OF APPLICATION, 1971-1974 IN KNOX COUNTY, TEXAS
^lot
no. 1971
1 F]1
2 F 112.1, 5/17;
112.1 , 7/26
3 F,, 112.1 , 5/17
D
4 F4> 112.1, 5/14
5 F7, 112.1 +
L 4.7 tt,6/7
6 F^
7 F , 112.1, 5/17;
11.2, 7/26
3 Fg, 112.1, 5/17
9 F4, 112.1, 5/14
10 F,, 112.1 +
- 4.7 £*,6/7
11 Fn
12 Fg, 112.1, 5/17
13 Fr 112.1, 6/7
14 Fn
15 F,, 112.1 , 5/17;
° 11.2, 7/26
8/5, 8/23,
9/2
16 F4, 112.1, 5/14
17 F?, 112.1 +
^ 4.7 &f,6/7
18 Fn
19 F , 112.1, 5/17;
D 11.2, 8/6
8/23, 8/31,
9/8
1972
1st crop 2nd crop
Fll
F,, 11.2, 5/24
22.4, 6/28
F, , 112.1, 5/23
b
F4, 123.3, 5/19
F,, 112.1, 5/22
f
Fn Fn
Fg, 11.2, 5/24 F,, 22.4, 7/27,
0 22.4, 6/28 D 8/30, 9/18;
44.8, 10/4
Fg, 112.1, 5/23 Fg, 112.1, 7/27
F4, 123.3, 5/19
FQ> 113.2 + 134.5,
8 5/19
Fll
Fg, 112.1, 5/23
Fr 112.1, 5/22
Fll
F,, 11 .2, 5/26, 6/9;
22.4, 6/28
F4, 123.3, 5/19
Fr 112.1, 5/22 Fg, 112.1, 7/27
Fn Fn
F,, 11.2, 5/26, F,, 22.4, 7/27
ft 6/9, 22.4, b 8/30; 67.3,
6/21, 7/3 10/4
Fll
F6,
D
F6'
F4'
FT
I
F9'
F7>
/
F7'
F5'
F,,
I
Fn
Fg,
Fr
Fn
Ffi,
D
F4.
Fr
f t
F7'
1973
22.4, 6/12
44.8, 6/27, 7/9
116.6, 5/30
115.5, 5/29
122.2, 5/31
28.0 (plots) + 32.3
(15N subplots) +
38.8 NaBr, 5/5;
121.1 (plots)(5/29)
+ [91.5 (15N sub-
plots) + 109.7
(NaBr)] , 6/4
22.4, 6/12; 44.8,
6/27, 7/9; 44.8
NaBr, 6/27
116.6 + 107.6, 5/30
115.5 + 130.0, 5/29
122.2, 5/31
116.6, 5/30
122.2, 5/31
22.4, 6/12;
44.8, 6/25
115.5, 5/29
122.2, 5/31
28 0 (plots) + 32.3
(I5N subplots) +
38.8 (NaBr), 5/5;
121.1 (plots), 5/29
+ [91.5 (15N sub-
plots) + 109.7
(NaBr)] , 6/4
22.4 + 44.8
NaBr, 6/8; 44.8
6/25, 7/9
1974
F,0, 22.4 15N
subplots,
4/24; 116.6
+ 82.4, 6/6
F,, 28.0, 6/5,
b 6/19
Fg, 111.0, 5/29
F4, 112.1, 5/31
Fll
F7, 111.0, 5/29
' 113.2, 5/20
F,, 112.1, 5/31;
113.2, 5/20
F,,., 22.4 15N
IU (subplots),
4/24; 116.6 +
82.4, 6/6
Fg, 28.0. 6/6
continued
36
-------
TABLE 3 (continued).
Plot
no.
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
1971
F4, 112.1, 5/14
F9, 112.1 +
^ 4.7 lp6/7
Fll
F,, 112.1, 5/17
O
F,, 112.1, 5/17
D
F,, 112.1, 6/7
F,, 112.1, 6/7
1
F
11
F,, 112.1, 5/17;
0 22.4, 9/13
Fg, 112.1, 5/17
F4, 112.1, 5/14
F , 112.1 +
^ 4. 7 ££,6/7
tFn
F,, 112.1, 5/17;
0 11.2t, 9/2,
9/8; 22.3,
9/13.
F,, 112.1, 5/17
D
F4, 112.1, 5/14
F?, 112.1 +
d 4. 7 1$, 6/7
Fn
Fg, 112.1, 5/17
F] , 112.1 , 6/7
1972
1st crop
F4, 123.3,
Ffi, 113.2
8 5/19
Fll
F 112.1
U
F6. 112.1
U
Fr 112.1
F., 112.1
1
F-,,
11
Fg, 11.2,
6 6/9
F,, 112.1
b
F4, 123.3
F, , 112.1
1
Fll
F,, 11.2,
6 6/9;
6/21
F,, 112.1
D
F4, 123.3
FR, 113.2
8 5/19
F11
F,, 112.1
0
Fr 112.1
F,, 112.1
D
, 5/19
+ 134.5,
, 5/23
, 5/23
, 5/22
, 5/22
5/24,
, 5/23
, 5/19
, 5/22
5/26,
22.4,
, 5/23
, 5/19
+ 134.5,
, 5/23
, 5/22
, 5/23
2nd crop
F5'
FT
1
Fn
F,.
/
F7>
Fr
1
F
1
Fn
n
F6'
D
F6>
F4'
Fr
Fll F9'
F,, 22.4, 7/27, F,,
° 8/30, 9/18
Fg, 112.1, 7/27 F?)
F5>
Fr
Fn
F6'
Fr
F,, 112.1, 7/27, F,,
b 9/11; 44.8,
9/27
1973
115.5 + 130.0,
5/29
122.2, 5/31
116.6 + 107.6,
5/30
116.6 + 107.6,
5/30
122.2, 5/31
122.2, 5/31
22.4, 6/13;
44.8, 7/2
116.6, 5/30
115.5, 5/29
122.2, 5/31
28tO (plots) + 32.3
(15N subplots) +
38.8 (NaBr), 5/5;
121.1 (plots), 5/29
+ 91.5 [(15N sub-
plots) + 109.7
(NaBr)], 6/4
22.4, 6/13; 44.8,
6/27, 7/10; 44.8,
NaBr, 6/27
116.6 + 107.6,
5/30
115.5 + 130.0,
5/29
122.2, 5/31
116.6, 5/30
122.2, 5/31
116.6 + 107.6,
5/30
1974
F., 112.1, 5/31
l\
F11
F,, 111.0, 5/29
U
Fg, 111.0, 5/30
F,, 111 .0, 5/30
6 113.2, 5/20
F,, 111.0, 5/30;
6 113.2, 5/20
F
^
Fln, 22.4 (15N
IU subplots),
4/24; 116.6
+ 82.4, 6/6
F,, 28.0, 6/5,
5 6/19
F,, 111.0, 5/29
6
F3, 112.1, 5/13
F11
F,, 111 .0, 5/29;
1 113.2, 5/20
F,, 112.1, 5/30;
J 113.2, 5/20
F,, 111.0, 5/29
D
rnnti niioH
37
-------
TABLE 3 (continued).
Plot
no.
41
42
43
44
45
46
*F1
F2
F3
F4
F5
F6
F7
F8
F9
1971
F6
FT
F6
F6
F!
F6
- Anhydrous Ammonia
- Anhydrous Ammonia +
Anhydrous Ammonia +
Sulfur Coated Urea
- Sulfur Coated Urea +
- Nitrogen Solution
- Nitrogen Solution +
1st crop
, 11.2, 5/24,
6/9, 6/27
!
, 112.1, 5/23
, 11.2, 5/24
22.4, 5/19,
7/3
1
, 11.2, 5/26;
22.4, 6/30,
7/11
N-Serve
Sodium Bromide
Sodium Bromide
Sodium Bromide
1972
2nd crop 1
F,, 22.4, 7/27, F, , 22.4
b 8/30, 9/11; D 44.8
44.8, 9/27
Fll Fll
F,, 112.1, 7/27 F,, 116.
0 0
F,, 22.4, 7/27, F,, 22.4
° 8/30, 9/11 ° NaBr
44.8, 9/27 44.8
7/7
Fn Fn
F7, 22.4
7 44.8
7/9;
NaBr
973 1974
, 6/7; F,, 28.0, 6/5,
, 6/22, 7/7 J 6/19
Fll
6, 5/30 Fg, 111.0, 5/29
+ 56.0 F,, 28.0, 6/5
, 6/7 b 6/19
, 6/22,
Fll
, 6/13; F , 28.0, 6/19
, 6/25, °
56.0
, 6/22
- Sodium Nitrate + Sodium Bromide
- Sodium Nitrate + two
small plots of
N-enriched Sodium Nitrate +
Sodium Bromide
F.
10
15,,
- Sodium Nitrate + 1/2 of two small plots in Fg fertilized with N-enriched Sodium Nitrate
'11
t 1971 - 2nd crop — All plots received 37 kg/ha superphosphate, 5/19.
1972 - 2nd crop — All plots received 9.0 kg/ha Zn as zinc sulfate, 7/26, and Plots 43-45 received
38 kg/ha phosphorus as superphosphate, 7/25.
1973 - All plots received 28 kg/ha N (liquid) 5/2-4 except 6, 18, 32.
1974 - All plots received 28 kg/ha N (liquid) to all plots, 6/22-24.
*l- liter
38
-------
Particle Size Analyses and Bulk Density
Particle Size Analyzes--
During the installation of the 9.1-m access tubes, it was found that
considerable variability existed in soil texture below the soil surface.
Particle size analyses were then made of a number of the holes to determine
the extent of this variability at the field site. Since the clay content
of a soil has a major influence on solute and water movement, plots of the
clay content on the two ends of the field site were graphed to show the
variability that existed at the site (Figures 10 and 11). The soil ranges
in clay content from 5 to 40% and is more variable in clay content below the
surface than the alluvial soils in many of the irrigated valleys in the
western United States. The profile is characterized by increases and
decreases in clay content between the surface and the water table. This
characteristic has a major influence on the soil-water retention properties
of the soil profile. As pointed out by Miller (17,18), for water to move
through layers with a clay content greater than depths below, an excess of
water must be present in the layer of higher clay content. This in turn
causes a higher soil-water potential and content than if the soil profile
were uniform. This fact has implications relative to the water quality of
irrigation return flows. Since the soils will retain more water than would
be expected based on textural characteristics alone, more water is available
for crop utilization. For those periods when crops are not growing, the
soils have a "reserve" holding capacity to retain water from unscheduled
rains and keep it from becoming return flow. Since such utilization of
existing soil characteristics would be an economical method of keeping water
from return flows, a survey of soil maps and characteristics may be worth-
while to determine the extent of layered soils in irrigated areas.
The heterogeneity of the soil precludes any possibility of using a
classical model for predicting water and solute movement. As will be
discussed later, an empirical approach was developed.
Bulk Density--
Bulk density, as well as soil texture, may influence movement of water
and solutes. Bulk density was determined with a calibrated density probe
(Model 1351, Troxler Electronic Laboratories, Inc., Research Triangle Park,
North Carolina) on all access probe holes on the field site. Bulk densities
of the north end of the main field site are graphed in Figure 12. As would
be expected, the bulk density was quite variable. In general, bulk density
increased with depth from 1.40 to 1.55 at the surface to 1.70 to 1.90 at
7.6 m. However, there were high density and low density "pockets" located
throughout the profile. It would be expected that this variability in bulk
density would have a definite effect on water and solute movement.
As will be discussed later, bulk density had a definite effect on the
soil-water content values. It was therefore necessary to correct the soil-
water content values for bulk density.
39
-------
0.0
6.1
100
200
300
DISTANCE, m
400
500
600
Figure 10. Clay content between the surface and the water table at the south end of the water
quality research site at Munday, Texas.
-------
0.0
100
200
300
DISTANCE, m
400
500
600
Figure 11. Clay content between the surface and the water table at the north end of the water
quality research site at Munday, Texas.
-------
0.0
ro
7.6
100
200 300 400
DISTANCE, m
500 600
Figure 12. Bulk density between the surface and the water table of the north end of the field site,
Munday, Texas.
-------
Irrigation
Systems--
As previously discussed, there was some problem in obtaining emergence
over the subirrigation system the first year (1971) when the crop was
planted on the bed rather than in the furrow. However, this was a problem
with planting rather than the irrigation system itself. In general, the
systems performed without problems the first year of the study. The 1.8-m
risers on the sprinkler system were found to be undesirable for corn in the
early stages of growth. These were reduced to 0.9-m risers prior to the
initiation of the 1972 growing season. This reduced drift and possibly
evaporation losses during the early part of the growing season.
The manual subirrigation system was besieged with minor problems. Most
of these were water leaks found during flushing of the system prior to the
growing season. Several control valves had frozen and split during the
winter months. Almost all pressure gauges had to be replaced. Many leaks
occurred in the laterals during the growing season due to gophers eating
holes in the polyethylene pipe. A rodent repellent was applied through the
system to the plots where the gophers did the most damage. Other leaks
found in the laterals were due to splitting of the pipe around connectors
where it had been repaired once before. Some stoppage of orifices occurred.
The filters were changed only at the beginning of the growing season.
A few problems occurred with the automation in the automated subirriga-
tion system. These were associated with vacuum switches on the switching
tensiometers and the solenoid valves. The vacuum switches were replaced
witn a switching-type tensiometer gauge manufactured by Irrometer Company.
Satisfactory operation occurred thereafter.
Sand passed through the 350 u filter and plugged the orifice in the
diaphram of the solenoid valves. This problem was solved by replacing the
350 y filters with 100 y filters. It was necessary to replace these filters
three times during the growing season even though they were washed period-
ically. Other solenoid valve trouble occurred due to the corrosion of the
brass interior which caused the diaphram to remain closed when the valve
was activated. This problem was solved by periodically applying a thin coat
of vacuum stopcock grease to the sides of the diaphram and interior wall of
each valve. Poor connections in electrical plugs exposed to the weather
created minor problems.
The only problem with the trickle irrigation system was external plug-
ging of the orifices. This was primarily due to sand blowing into the
orifice outlet and crusting while the system was not operating. Other
plugging occurred due to algae growth in the orifices.
Plugging also occurred in the subirrigation systems. The automated
subirrigation systems used in this study (Plots 40 through 45) were
installed in 1972. In 1973, individual plants were observed to be water-
stressed, indicating the presence of plugged emitters. Each of the six
plots consisted of 16 laterals with approximately 73 emitters per lateral.
43
-------
These were Whitney orifices (manufactured by Submatic, Inc., 709 27th St.,
Lubbock, Texas) with a 0.56-mm diameter opening.
The number of plugged emitters in each lateral in each plot was esti-
mated from the locations of water-stressed plants. Plugged emitters were
excavated, removed from the lateral, and inspected to determine the cause
of plugging. Then four entire laterals in Plot 40 were unearthed to deter-
mine the number of plugged orifices which were not located by plant inspec-
tion.
Two causes of plugging were observed. Orifices were plugged by root
hairs and by sand particles. The number of plugged emitters located in each
plot by plant inspection was multiplied by the ratio of total plugged
emitters to plugged emitters determined by plant inspection in Plot 40 to
obtain an estimate of total number of plugged emitters in each plot. These
values are given in Table 4. An average of 5% of the emitters were plugged
by sand and 7% by roots. Twelve percent of all emitters were plugged after
one season of use.
TABLE 4. PERCENT OF EMITTERS IN AUTOMATED SUBIRRIGATION
PLOTS PLUGGED AFTER ONE SEASON OF USE
PlotPercent plugged
no. By sand By roots Total
40 8 15 23
41 4 10 14
42 448
43 8 4 12
44 448
45 4_ _2 _6
Avg. 5 7 12
Water Applied at Each Irrigation--
A summary of the amounts of irrigation water applied at each irrigation
to the different plots is given in Table 5. During the first year of the
study (1971), 7.6 cm were applied to the sprinkler- and furrow-irrigated
plots per irrigation and only 5.0 cm were applied to the subirrigated plots
per irrigation using the criteria stated in Table 5. The reason these
amounts were used was that 7.6 cm was the amount required to obtain good
distribution on the furrow-irrigated plots. Based on the preliminary work
with distribution of water from the subirrigation system, 5.0 cm appeared
to be adequate to return the root zone to field capacity.
It was obvious that these were poor criteria for scheduling irriga-
tions. Therefore, in the remaining years the amounts of water added were
based on potential ET with the amounts added being variable except for the
furrow irrigation systems where a 7.6-cm minimum was required to obtain
good distribution. Another exception was in 1974 when two and three times
potential ET were added to determine the influence on ion movement. In
44
-------
TABLE 5. SUMMARY OF THE AMOUNTS OF WATER APPLIED AT EACH IRRIGATION TO THE
DIFFERENT PLOTS AT THE FIELD SITE NEAR MUNDAY, TEXAS, 1971-1974
Year
1971 Plots 1-13 (sprinkler-irrigated) and Plots 14-26 (furrow-irrigated)
received 7.62 cm and Plots 27-39 (subirrigated) received 5.08 cm
when leaf curl or designated potential level occurred.
1972 Plots 1-39 received 2.54- to 7.62-cm irrigations with the actual
amount being a percentage of potential ET based on stage of growth
(LAI) when leaf curl or designated potential level occurred.
Plots 40-45 (automatically subirrigated) and Plot 46 (automatically
drip-irrigated) received 0.23- to 1.45-cm irrigations with the
actual amount being that required to lower the potential below the
preset level of the switching tensiometer.
1973 Plots 1-39 received 3.68- to 8.00-cm irrigations with the actual
amount based on the criteria used in 1972.
Plots 40-46 received 0.03- to 1.88-cm irrigations with the actual
amount based on the criteria used in 1972.
1974 Plots 6, 7, 11, 18, 19, 22, 24, 32, 33, and 37 received 2.92- to
10.54-cm irrigations with the actual amount based on the criteria
used in 1972.
Plots 8, 12, 19, 25, 34, and 38 received 5.08- to 16.26-cm irriga-
tions with the actual amount based on two times the criteria used
in 1972.
Plots 9, 13, 23, 26, 35, and 39 received 5.08- to 20.57-cm irriga-
tions with the actual amount based on three times the criteria used
in 1972.
Plots 40-46 received 0.08- to 3.73-cm irrigations with the actual
amount based on the criteria used in 1972.
practice, not quite three times potential ET were added because the amount
of water required was unrealistic from a practical standpoint.
The amounts added at each irrigation through the automated systems
were usually less than 2.5 cm. It should be pointed out that although the
potential levels were preset on the switching tensiometers between -20 to
-40 cb, varying according to the year, the potential increased approxi-
mately -10 cb above the preset level due to the lag in the time required
for the water to move from the orifices in the irrigation systems to the
tensiometer. As will be discussed later, these frequent small amounts
were a factor in creating some extremely high irrigation water-use
45
-------
efficiencies. However, it should also be pointed out that these relatively
constant high moisture levels apparently caused problems with roots growing
into the orifices of the subirrigation systems.
Water Applied Prior to Emergence--
The amounts of water applied prior to crop emergence are given in
Table 6. The amounts ranged from 0 to 20.3 cm. As previously discussed,
the largest amount was required to obtain emergence of corn planted on the
bed over a subirrigation system on the second planting in 1971. A subse-
quent second planting in the same year required only 2.5 to 5.0 cm to obtain
emergence.
TABLE 6. AMOUNTS OF WATER APPLIED PRIOR TO EMERGENCE TO THE DIFFERENT PLOTS
AT THE FIELD SITE NEAR MUNDAY, TEXAS, 1971-1974
Year
1971
1972
1973
1974
Plot
no.
1-13
14-26
27-39
27, 28, 32
33
1-13
14-26
27-36
37-39
40-45
46
6-8, 17-19, 32-34
40-41
42
43-45
1-46
6-9, 11-13, 18-20
Planting
1st
2nd
1st
2nd
1st
2nd
3rd
1st
2nd
Amount,
cm
7.62
5.08
7.62
6.35
7.62
20.32
5.08
2.54
None
7.62
None
5.08
2.54
1.27
7.62
4.75
4.67
4.62
None
5.08
22-26, 32-45
In 1972, no water was applied prior to emergence in the sprinkler-
irrigated and most of the subirrigated plots at the first planting. Amounts
46
-------
of 4.6 to 7.6 cm were required to obtain emergence on the second planting.
No water was applied to obtain emergence in 1973, and 5.0 cm were applied in
1974.
In summary, the amount of irrigation water required to obtain good crop
emergence varied between years. These soils are self-mulching and will
store adequate moisture for planting for several months. If water is not
available to be stored, approximately 5.0 cm are adequate to obtain crop
emergence.
Water Applied During Growing Season--
The amounts of water applied during the growing season are given in
Table 7. If the average amounts applied through the sprinkler and manual
subirrigation systems are compared to the furrow systems, one can see that
the sprinkler and subirrigation systems were consistently superior following
the first year of the study when water applications were based on amounts
rather than potential ET and leaf area. In 1971, the sprinkler system had
the greatest amount applied (35.8 cm) followed by the furrow (30-1 cm) and
manual subirrigation systems (17.8 cm). The furrow system had the greatest
average amount applied in 1972 (22.1 cm) followed by the subirrigation
(18.4 cm) and the sprinkler system (16.6 cm). The furrow irrigation system
had the greatest amount applied in 1973 (35.2 cm), while the sprinkler and
subirrigation systems were equal in the average amount applied (24.8 cm).
In 1974, the greatest average amount was applied through the furrow irriga-
tion system (32.2 cm) followed by the manual subirrigation system (27.1 cm)
and the sprinkler irrigation system (26.0 cm). These data suggest that
little difference exists among manually-operated systems relative to irriga-
tion water-use efficiency if scheduling is done on the basis of potential ET
and the system is designed so that adequate distribution can be obtained.
It was not possible to apply only the amounts based on potential ET and leaf
area through the furrow system due to the porosity of the soil at the site.
Significantly less irrigation water was required by the automated
irrigation systems with the average amounts required ranging from 10.9 to
16.7 cm or almost 50% less than using manual systems and irrigating on the
basis of potential ET or set amounts using stage of growth or water poten-
tial as a criteria for applying water. These significant differences will
be discussed in detail in a later section.
Soil Water Potential
During the first year of the study, no problems were encountered with
the tensiometers in measuring soil-water suction. They were read three to
six times weekly at 0.13 to 1.27 m and weekly at 1.27 to 2.54 m.
Many of the tensiometer gauges were inoperable at the beginning of the
1972 season due to freezing in storage. After the gauges were replaced,
the tensiometers functioned without problems. All of the tensiometers were
read three times weekly and serviced at least once every two weeks. Some
of the shallow depth tensiometers (0.13 to 0.26 m) had to be serviced more
frequently. Since adequate soil data were obtained in 1971 and 1972 on
soil-water suction at Location 2, all but the 0.13, 0.25 and 0.38 m
47
-------
TABLE 7. AMOUNTS OF WATER APPLIED (CM) DURING THE GROWING SEASON TO THE DIFFERENT PLOTS AT THE FIELD SITE NEAR MUNDAY, TEXAS, 1971-1974
CO
Year 1
1971 22.86
1972 20.32
1973 21.97
1974
1972
14
1971 38.10
1972 17.78
1973 38.10
1974
1972
27
1st
1971 7.62
1972 20.32
1973 20.57
1974
2nd_
1971 5.08
1972
40
1st
1971
1972 17.17
1973 13.34
1974 17.78
1974
2nd
1972 11.96
2
30.48
20.96
25.53
15
30.48
17.78
38.10
28
1st
7.62
15.88
20.57
2nd
5.08
41 "
1st
13.16
13.18
15.54
2nd
4.19
3
22.86
27.94
20.32
16
30.48
25.40
38.10
29
12.70
27.94
25.65
42
1st
10.54
18.75
15.70
2nd
5.51
4
53.34
29.21
25.53
17
1st
22.86
25.40
30.48
2nd
T5724
30
17.78
27.94
22.48
43
1st
8.74
12.95
11.23
2nd
10.49
5
30.48
27.94
22.48
18
1st
30.48
10.16
38.10
30.96
2nd
5.08
31
15.24
31.75
22.48
44
1st
8.31
12.65
15.75
2nd
10,49
6
Ts~F
45.72
20.32
25.65
25.40
2nd*
5.08
19
1st
53.34
22.86
38.10
30.48
2nd
10.16
32
1st
5.08
20.96
25.65
25.53
2nd
5.08
45
1st
9.07
13.28
9.12
2nd
7.32
7
1st
53.34
20.96
25.65
24.89
2nd
TT743
20
38.10
25.40
30.48
49.53
33
1st
7.62
24.77
26.29
26.42
2nd
11.43
6.35
46
9.30
15.24
31.65
Plot
8
1st "
38.10
20.32
25.53
58.04
2nd
5.08
21
45.72
27.92
38.10
34
1st
22.86
24.13
25.65
42.42
2nd
10.16
no.
9
53.34
29.21
25.65
70.92
22
20.32
22.86
31.17
29.08
35
33,02
31.75
25.65
44.70
10 11
38.10 25.40
21.59 20.32
25.53 25.65
27.81
23 24
20.32 20.32
22.86 22.86
32.05 34.82
53.85 38.10
36 37
35.56 20.32
36.83 25.40
28.30 26.29
29.41
12
25.40
27.94
26.42
58.04
25
20.32
22.86
34.82
50.04
38
22.86
33.02
26.42
56.52
13
25.40
27.94
26.42
74.80
26
20.32
22.86
34.82
61.72
39
22.86
33.02
26.40
57.66
1st crop,
avg
35.76
24.23 (16.61 if 7.62 on required for sampling is
24.79 eliminated)
48.56 (All plots)
26.03 (Plots irrigated on basis of potential ET)
1st crop,
' avg
30.09
22.08
35.18
42.98 (All plots)
32.15 (Plots irrigated on basis of potential ET)
1st crop,
avg
17.78
27.20 [18.40 if water required for sampling (7.62 cm)
24.80 and crop establishment (5.08 in
40.39 (All plots) plots 37, 38, 39) are eliminated]
27.12 (Plots irrigated on basis of potential ET)
1st crop,
avg
10.90
14.20
14.20 (Excluding Plot 46)
16.68 (Including Plot 46)
*Crop for year indicated
-------
tensiometers were removed from this location prior to the 1973 growing
season. Tensiometers were removed from plots not used in 1974.
Specific relationships of soil-water potential and irrigation return
flow will be discussed later in the report. Therefore, only generalities
will be discussed at this time. Figure 13 shows the depth potential rela-
tionships of plots from the sprinkler irrigation, furrow irrigation,
subirrigation and automated subirrigation systems. Both the matric and
total potentials are shown along with the clay content at the different
depths. It can easily be seen that the greatest change in potential for
all irrigation systems occurred at 15 cm and varied from -70 to 0 cb total
potential. In the sprinkler, furrow, and manually-subirrigated plots,
there was considerable change at 30 cm with the range being -52 cb to -2 cb,
-57 to -2 cb, and -35 to 0 cb, respectively. The automated subirrigation
plot only fluctuated from 0 to -10 cb during the year. This was the depth
at which the switching tensiometer was located in the soil, and it appears
that the potential remained fairly constant at this depth. The amount of
fluctuation at 46 cm was least in the sprinkler-irrigated plots (-6 to
-8 cb) followed by the manual subirrigated plots (-4 to -8 cb), automated
subirrigated plots (-3 to -10 cb) and furrow-irrigated plots (-6 to -18 cb).
Fluctuation between 46 cm and 1.5 m was greatest in the subirrigation plots,
intermediate in the furrow-irrigated plots, and least in the sprinkler-
irrigated plots. These trends generally held true for all plots in each
system. More water was used from the lower zones in subirrigation systems
than in the furrow systems. The least amount of water was used between
46 cm and 1.5 m in the sprinkler system. In general, there was little
difference (<10 cb) in the change in potential between the plots of the
different irrigation systems below 1.5 m. The exception was the sprinkler-
irrigated plot at 2.4 m which increased from -36 cb to -18 cb. This
appeared to be a relatively dry zone which increased in potential as water
was added.
Texture had a major influence on the potential curves. Generally, the
potential was greater in zones of lower clay content that were immediately
above zones of higher clay content; i.e., 1.8 m vs 2.1 m in the sprinkler-
irrigated plot, 2.4 m vs 2.7 m in the furrow-irrigated plot, 1.5 m vs 2.1 m
in the manual subirrigated plot, and 1.2 m vs 1.8 m in the automatically-
subirrigated plot. The potential at "field capacity" was -10 cb or greater
in these zones, suggesting that this is a characteristic common to layered
soils. If this is true, these soils hold more water than one would normally
expect from the commonly accepted -33 cb value. This characteristic could
be of value in maintaining the quality of irrigation return flows in that
it extends the previously reported range of potential from -33 cb to -10 cb,
allowing more water to be stored in the soil profile before significant
drainage occurs. There was a trend for the potential gradient to increase
down from 46 cm to 3.0 m. However, there were exceptions to this (2.4 m in
the sprinkler-irrigated plots, 1.5 and 2.4 m in the furrow-irrigated plots,
1.5 and 3.0 m in the manual subirrigated plots, and 1.2, 1.8 and 3.0 m in
the automaticallyT-subirrigated plots). In general, these zones were in or
immediately above the zones of highest clay content. The textural
influences will be discussed in more detail under the section on hydraulic
conductivity (K). As would be expected, there was an upward gradient
49
-------
CLAY,
2.4 -
3.0
10
20 30 40 50
POTENTIAL, -cb
60
FURROW-IRRIGATED
O - MINIMUM TOTAL
POTENTIAL
• - MAXIMUM TOTAL
POTENTIAL
A - MINIMUM MATRIC
POTENTIAL
- MAXIMUM MATRIC
POTENTIAL
I
10 20 30 40 50
POTENTIAL, -cb
60
CLAY,
-------
between 15 and 46 cm and the surface due to the evaporative demand of the
atmosphere and crop use.
Soil-Water Content
As previously mentioned, 5.08-cm diameter access tubes were installed
at two locations to 9.1 m in each plot to obtain soil-water content read-
ings. Data were taken at 0.30-m increments periodically in each plot where
possible. In some plots the tubes were bent and in others the welded caps
on the bottom had leaks so that water from the water table entered the tube
making it impossible to obtain readings for the full depth.
Calibration of Neutron Probes--
In this section only general observations concerning water content will
be made. During the first year of the study, the neutron probes were not
calibrated, therefore only relative changes in soil-water content were
measured. During the second year of the study, standards were constructed
by packing soils of various textures and moisture contents obtained at the
site to different bulk densities. Figures 14 and 15 show the moisture-count
ratio curves obtained for the two probes used in the studies. Figures 16
and 17 show the relationship between moisture content (6)/count ratio (CR)
and bulk density for the two probes.
Figure 18 shows the relationship between counts and wet density of all
soil textures for the density probe used in the study. It is interesting to
note that textures did not influence the counts at a particular bulk density
and that the relationship between wet density and counts was good for all
textures (r - 0.9815).
Comparison of Corrected and Uncorrected Soil-Water Content Values for
Troxler Neutron Probe--
Figure 19 shows the relationship between the values for 6 using the
standard curve from the manufacturer of the neutron probe and values for 6
using the curves developed from standards made from soils at the site. It
can be readily seen that there is a major difference between the values for
9 obtained using the two curves. The uncorrected values are higher than
the corrected values by 1 to 16% by volume. The differences between the
corrected and uncorrected values increased with depth. Maximum difference
at the high moisture content was 10% by volume and at the low moisture
content 16% by volume. This suggests that the error was greater at lower
values of soil-water content than at higher values of soil-water content.
As will be discussed later, the ability to detect these differences is
very important.
A comparison of the uncorrected differences indicates that the value
differences were small between the maximum and minimum soil-water content
below 1.5 m (<1% by volume) while differences in corrected values were 2 to
5% by volume. This indicates that the uncorrected readings were less sensi-
tive to changes than the corrected readings. The sensitive values were
more desirable for evaluating predictive models.
51
-------
24
22
20
18 -
16 -
LU
1 14
12
o
>
>-
O
O-
*s
CD
10
8
6
A-
2
0
0
O
o
o
o
0 = 27.899-CR + 0.8673
(' ' •: ' ' ' -I, , ',' f>- H \ "n • , ' " "'•
r = 0.958
.1 .2 .3 .4 .5 .6
COUNT RATIO, CR
.7 .8
.9 1.0
Figure 14-
Relationship between 6 and count ratio for Troxler neutron
moisture probe No. 1 used at the field site near Munday,
Texas.
52
-------
LU
s:
ZD
_i
o
>
>-
h-
•z.
LU
LU
CL.
ft
CD
o
6 = 27.454 CR + 0.9277
r = 0.969
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0
COUNT RATIO, CR
Figure 15. Relationship between 6 and count ratio for the Troxler
neutron probe No. 2 used at the field site near Munday,
Texas.
53
-------
38
36 h
34
.32
.30
o
w -28
.26
.24
.22
.20
1.0
o
o
o
o
= -0.3026 B.D. + 0.7078
r = -0.907
1.1
1.2
o
o
o
1.3 1.4
BULK DENSITY, g/cc
O
1.5
1.6
1.7
Figure 16. Relationship between 6/count ratio and bulk density for Troxler neutron probe No. 1
used at the field site near Munday, Texas.
-------
on
Oi
,38
.36
,34h
.32
.30
.28
.26
.24
.22
.20
i- o
1.0
o
o
o
o
- = -0.3006 B.D. + 0.7091
LK
r = -0.915
o
o
1.1
1.2
_L
O
1.3 1.4
BULK DENSITY, g/cc
1.5
1.6
1.7
Figure 17. Relationship between 6/count ratio and bulk density for Troxler neutron probe No. 2
used at the field site near Munday, Texas.
-------
70!
60
-o
rcj
CO
O
-C
o
o
50
40
30
20
10
Dw = 3.127 e
r = 0.9815
-0.000023029 (COUNTS)
1.0
Figure 18.
1.4 1.6
WET DENSITY, g/cc
1.8
2.0
Relationship between counts and wet density for the Troxler
density probe used to determine the bulk densities of the
field site near Munday, Texas.
Comparison of Troxler and Well Reconnaissance Probes--
The characteristics of the standards used to calibrate the neutron
probes are shown in Table 8. In addition to the two Troxler probes, a
probe manufactured by Well Reconnaissance, Inc., on loan from the U. S.
Environmental Protection Agency, was also calibrated. Figure 20 shows
the relationship between 9 from the standards and the meter readout of
the probe. It can be seen that the texture had no influence on the
relationship. The high R value indicates that a good relationship existed
between the two parameters. A better relationship would probably have
been obtained if more data had been available.
Figure 21 shows the relationship between 6 (standards)/6 (Reconnais-
sance probe) vs bulk density. Although there was an effect due to density,
it was not as pronounced as with the Troxler probes (Figures 16 and 17).
However, there was a definite influence due to bulk density. Table 9
compares values obtained using the Company standards and constructed
56
-------
LOW VALUES FOR 9
HIGH VALUES FOR 0
en
-vl
£
1 —
Q_
LU
Q
0.0
1.5
3.0
4.6
6.1
7.6
9.1
•^•B
C(
-
-
UNCORRECTED
CORRECTED
UNCORRECTED
CORRECTED
10 20 30 40
9, percent by volume
50
10 20 30 40
9, percent by volume
50
Figure 19. Comparison of uncorrected values for 9 using the standard curve from the Company and
corrected values for 9 using the curve developed from standards made of soils at the
site having different bulk densities.
-------
TABLE 8. CHARACTERISTICS OF STANDARDS USED TO CALIBRATE NEUTRON PROBES
Standard
number
1
2
3
4
5
6
7
9
10
11
12
13
14
15
16
Particle size,
I
Sand
42
42
42
42
42
42
60
60
60
60
76
76
76
76
76
Silt
35
35
35
35
35
35
20
20
20
20
13
13
13
13
13
Clay
23
23
23
23
23
23
20
20
20
20
11
11
n
n
n
Bulk
density,
g/cm3
1.21
1.40
1.02
1.29
1.10
1.30
1.20
1.21
1.20
1.40
1.31
1.45
1.61
1.35
1.55
Wet
density,
g/cm3
1.25
1.45
1.11
1.38
1.25
1.53
1.39
1.24
1.29
1.49
1.34
1.65
1.81
1.45
1.65
Moisture
content,
% by volume
4.05
4.82
8.70
9.18
14.87
22.88
18.80
3.44
8.85
9.00
3.38
19.88
19.78
9.80
10.20
Q- 23% CLAY 422 SAND
Q- 20% CLAY 60% SAND
A- 11% CLAY 76% SAND
10 12 14 16 18 20 22 24 26
6, RECONNAISSANCE PROBE READING
Figure 20. Relationship between 6 and probe reading for the Recon-
naissance probe on loan from the U. S. Environmental
Protection Agency.
58
-------
1.8
1.7
1.6
1.5
1.4
o 1.3
«* 1.2
1.1
1.0
0.9
0.8
0.7L
0.6
O
• BULK DENSITY
OWET DENSITY
1.0
Figure 21.
O
y = 2.5613 - .9865 X (WET DENSITY)
r = .673
y = 1.585 - .330 X (BULK DENSITY)
r = .338
O
. o\ o
O
1.2 1.4 1.6
BULK DENSITY
1.8
2.0
Relationship between e/meter reading and density
for the Reconnaissance probe.
standards. It can be readily seen that data correction using a calibration
curve from the constructed standards shows a better distinction between
zones with higher and lower soil-water contents, especially at the top and
bottom of the profile. The surface 0.9 m is lower in bulk density and the
differences between readings were not as great, and the moisture contents
were relatively high compared to those in the middle of the profile. The
water table beginning at 7.0 m was much more pronounced in that the values
at 7.0 m and below were 3 to 6% higher than the layers immediately above.
Where measurements from the profile were based on standards from the
Company, it was not possible to distinguish where the water table began
with the Well Reconnaissance probe and difficult with the Troxler probe in
that the difference was only slightly over 2%. This difference was approx-
imately 6% when the calibration curve from the constructed standards was
used.
59
-------
TABLE 9. COMPARISON OF MOISTURE CONTENT (PERCENT BY VOLUME) VALUES
OBTAINED BY A TROXLER NEUTRON PROBE AND A WELL RECONNAIS-
SANCE, INC., NEUTRON PROBE
Troxler
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
3.4
3.7
4.0
4.3
4.6
4.9
5.2
5.5
5.8
6.1
6.4
6.7
7.0
7.3
7.6
7.9
8.2
Bulk
density
1.51
1.42
1.54
1.61
1.67
1.70
1.70
1.75
1.75
1.75
1.72
T.78
1.81
1.78
1.81
1.83
1.82
1.76
1.77
1.73
1.77
1.78
1.64
1.70
1.67
1.70
1.73
*
21.87
20.08
19.70
21.24
20.44
20.43
20.90
24.42
27.29
26.77
25.00
26.12
27.17
28.07
27.74
27.42
27.96
29.29
29.11
29.02
28.46
28.12
30.98
31.04
31.40
30.18
29.69
t
19.54
19.66
16.66
16.64
14.82
14.12
14.39
15.75
17.55
17.12
16.95
16.05
15.86
17.30
16.17
15.41
15.93
18.46
18.23
19.46
17.71
17.26
23.62
21.77
22.92
21.13
19.89
Well
Reconnaissance
*
19.4
21.2
20.0
20.1
21.8
20.1
20.7
21.0
24.0
26.0
25.5
25.6
26.2
25.5
27.0
26.6
26.5
27.0
27.1
27.8
26.6
26.6
25.9
28.0
28.5
28.0
27.9
t
17.69
21.71
17.69
16.27
16.46
14.32
14.82
13.93
16.25
17.80
18.27
16.63
16.18
16.55
16.74
15.86
16.10
18.26
18.04
17.86
17.66
17.36
20.92
20.43
22.32
22.93
19.90
rBasea on company standards.
fBased on constructed standards and corrected for bulk density.
60
-------
Comparison of Soil-Water Content Changes of Various Irrigation Systems
During the Growing Season--
The small change in soil-water content (2 to 5% by volume) in a given
season was typical of all soil profiles in all irrigation systems. Figure 22
shows the maximum and minimum soil-water content in profiles from the four
irrigation systems. The small change in water content indicates the excel-
lent possibility of water losses to irrigation return flow. The water
content varied more in the automatically-irrigated system than in the other
systems.
The clay content varied from 9 to 38% within the soil profile. As will
be discussed later, the zones of high sand or low clay content created
problems relative to obtaining soil-water extracts. In some cases, soil-
water extracts were never obtained from zones which had high sand contents
or low clay contents. This was probably due to a combination of low soil-
water content and poor contact between the soil and the porous bulbs.
Soil-Water Content Changes Between Years--
Figure 23 shows the changes in soil-water content during the four years
of the study in one of the sprinkler-irrigated plots. During the first
growing season (May 11 to July 18, 1971), change in soil-water content was
between 0 and 3.0 m. The water content increased over 5% by volume between
1.2 and 1.8 m. Between May 11, 1971 and April 12, 1972 there was a further
increase in soil-water content in a portion of this zone (0.9 to 2.4 m) and
a major increase to a depth of 7.6 m. This was due to the 32.9 cm of rain
received during this period. The water table rose from 6.1 to 5.5 m.
During the 1972 crop year (April 12 to July 18, Figure 23), there was
little change in soil-water content in the profile. However, between
July 18, 1972 and May 8, 1973, there was another major increase in soil-
water content between 4.6 and 6.1 m, indicating a further rise in water
table due to rainfall (74 cm) received between the two dates. The fact that
there was little change in water content above these two zones indicates
that the zones were at "field capacity" and could not retain more water and
that the increase was due to recharge in another area.
Except for minor changes in the surface, the major changes in water
content during the 1973 growing season were between 4.6 and 6.1 m. The
decreased water content indicated that the water table receded during this
period. With the exception of the surface samples, there was little change
between May 1973 and July 1974. The soil-water content on the first date
of the study is included in this figure to delineate the overall changes
during the course of the study. It can be seen that the water content
increased from 2 to 8% between the surface and the bottom of the profile.
This was true of all plots. Thus, the area has a fluctuating water table,
and irrigation enhances the possibility that excess water from rainfall and
irrigation and excess nitrates from fertilization will reach the water table
by increasing the soil-water content of zones that might otherwise be dry
under nonirrigated conditions.
61
-------
SPRINKLER IRRIGATION
FURROW IRRIGATION
0.0 r-
9.
WATER TABLE
J L
30 40 0 10
SOIL WATER CONTENT, VOLUME %
i i I I
20 30 40
MANUAL SUBIRRIGATION
AUTOMATED SUBIRRIGATION
0.0
1.5 -
3.0
E 4.6
10 20
WATER TABLE
30 40 0 10
SOIL WATER CONTENT, VOLUME %
20 30 40
Figure 22. Maximum and minimum soil-water contents of profiles from the different
irrigation systems during 1972.
62
-------
0.0 i-
1.5 -
3.0
• 4.6
MAY 117
h 1971
Q_
UJ
Q
6.1
7.6
9.1
JULY 13,-
1971
APRIL 12,
1972
J I
JULY 18,
197
APRIL 12,
1972
10 20 30 40 0 10
SOIL-WATER CONTENT, volume
20
MAY 8, 1973
I I I
30
40
9.1 i
MAY 8,
1973
MAY 11,-
1971
NOVEMBER 13,
1973
JULY 3, 1974
30 40 0 10 20
SOIL-WATER CONTENT, volume %
30
40
Figure 23. Changes in soil-water content in a sprinkler-irrigated plot during the
course of the study.
63
-------
Hydraulic Conductivity Studies
A separate study was initiated in 1973 using small plots to determine
the hydraulic conductivity of the Miles loamy fine sand at the field site.
The conductivities were determined in 30-cm increments of the soil profile
between 15 and 290 cm according to the procedure of Hillel, et al. (9).
Tables 10 through 15 show the hydraulic conductivities (K) along with
the moisture content (e), matric suction (^), texture, and bulk densities.
The profiles had a wide range of textures (clay content 8 to 37%) and bulk
densities (1.39 to 1.67). The profiles were thus characterized by layers
having major differences in texture and bulk density. As would be expected,
the profiles exhibited considerable variability in soil-water characteris-
tics. In Figure 24, the hydraulic conductivities for the different depths
at one location are shown along with information on the soil texture and
bulk density. It can be seen that four layers in the profile had 16 or 17%
clay and 71 or 72% sand, yet the hydraulic conductivity curves show consid-
erable difference in hydraulic conductivity at a particular soil-water
content. In general, for a given soil texture, the highest water content
for a particular conductivity occurred in zones immediately above a zone of
higher clay content which was followed by zones of lower clay content. In
this profile, this was true for the zones located at 76 cm and 229 cm.
Although the clay content at 137, 167, and 198 cm was similar to that at
76 cm, and the content at 290 cm was similar to that at 229 cm, the zone
above the zones which had high clay content (107-cm and 259-cm zones) had
the highest moisture content for a particular hydraulic conductivity. The
curves differ considerably in soil-water content for a particular hydraulic
conductivity. They do, however, have some characteristics in common. The
slope of all the curves is very similar indicating the rates of change in
hydraulic conductivity for all depths are approximately the same. Further,
100-fold changes {0.254 to 25.4 millimeters per day (mm/da)] in hydraulic
conductivity may occur with an increase in soil-water content of only 2 to
6% by volume. If an average of 4% by volume is assumed, in a 4.6-m profile
(a depth at which the water table is often located) the addition of 184 mm
of water to the profile would cause increases in hydraulic conductivity from
less than 0.254 mm/da to over 25.4 mm/da. If the area had no crop, it is
possible that water from excess rainfall or excess irrigation would reach
the water table within one week.
Values for hydraulic conductivity were determined two to three times at
each location. A comparison of the values obtained as a function of soil-
water content and matric suction for the 76- and 229-cm depths are shown in
Figures 25 and 26, respectively, for Plot 1. It can be seen that the
conductivities at a particular soil-water content or matric suction vary
considerably between the dates at which the tests were run. This may be due
to differences in soil-water content of zones below the zones evaluated. It
is visualized that such differences may have existed between the two dates,
especially at Locations 1 and 2, because these were dryland plots prior to
the initiation of these studies. Plot 3 was an irrigated plot and there was
less change in hydraulic conductivity at a particular moisture content than
with Plots 1 and 2.
64
-------
TABLE 10. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND, KNOX COUNTY,
TEXAS, DURING SEPTEMBER 18 TO OCTOBER 3, 1973 AND OCTOBER 8 TO OCTOBER 29, 1973, AT
LOCATION 1
Experiment 1
September 18 to October 3,
Depth,
cm
15
46
76
107
137
168
198
229
259
290
Particle Bulk
size, density,
% g/cm3
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
86 1 .55
6
8
82 1.52
7
n
74 1.53
9
17
71 1.56
10
19
72 1.55
n
17
72 1.56
n
17
71 1.60
13
16
69 1.64
11
20
66 1.68
11
23
67 1.72
12
21
Time,
da
0.5
1.0
4.0
8.0
12.0
0.5
1.0
4.0
8.0
12.0
0.5
1.0
4.0
8.0
12.0
0.5
1.0
4.0
8,0
12.0
0.5
1.0
4.0
8.0
12.0
1.0
4.0
8.0
12.0
Matric
suction,
cb
-1.
-1,
1,
1
2,
-0
1
2
3
3
-0
0
2
2
3
0
1
3
4
4
1
2
5
6
6
2
4
5
6
.5
.5
.2
.8
.0
.3
.0
.6
.2
.5
.7
.8
.2
.7
.0
.0
.8
.7
.4
.9
.2
.9
.1
.1
.4
.8
.6
.6
.2
6,
crn3/cm3
.217
.206
.185
.168
.158
.253
.244
.237
.234
.232
.246
.242
.235
.232
.230
.229
.218
.204
.198
.195
.232
.221
.202
.196
.191
.219
.207
.199
.192
1973
K,
mm/da
21.69
8.84
4.23
2.87
2.44
71.51
18.72
5.93
3.95
3.96
17.43
4.09
0.88
0.51
0.26
40.92
10.00
1.34
0.71
0.42
25.23
9.08
1.87
0.91
0.57
61.89
13.60
11.18
5.39
Experiment 2
October 8 to October 29,
Time,
da
1.5
3.0
1.5
3.0
1.5
3.0
5.0
10.0
18.0
1.5
3.0
5.0
10.0
18.0
1.5
3.0
5.0
10.0
18.0
1.5
3.0
5.0
10.0
18.0
1 .5
3.0
5.0
10.0
18.0
1 .5
3.0
5.0
10.0
18.0
l
-------
TABLE 11. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND,
TEXAS, DURING SEPTEMBER 21 TO OCTOBER 5, 1973, LOCATION 2
KNOX COUNTY,
Depth,
cm
15
46
76
107
137
168
198
229
259
290
Particle size,
%
Sand 85
Silt 6
Clay 9
Sand 81
Silt 8
Clay 11
Sand 74
Silt 12
Clay 14
Sand 68
Silt 15
Clay 17
Sand 66
Silt 15
Clay 19
Sand 57
Silt 18
Clay 25
Sand 50
Silt 21
Clay 29
Sand 45
Silt 24
Clay 31
Sand 44
Silt 26
Clay 30
Sand 50
Silt 24
Clay 26
Sulk density,
g/cm3
1.49
1.45
1.42
1.45
1.52
1.65
1.74
1.71
1.62
1.60
Time,
da
0.7
1.5
3.0
6.0
10.0
15.0
0.7
1.5
3.0
6.0
10.0
15.0
0.7
1.5
3.0
6;0
10.0
15.0
0.7
1.5
3.0
6.0
10.0
15.0
1.5
3.0
6.0
10.0
15.0
0.7
1.5.
3.0
6.0
10.0
15.0
0.7
1.5
3.0
6.0
10.0
15.0
0.7
1.5
3.0
6.0
10.0
15.0
0.7
1.5
3.0
6.0
10.0
.15.0
0.7
1.5
3.0
6.0
10.0
15.0
Matric suction,
cb
-1.5
-0.9
-0.1
1.0
2.0
2.5
-1.3
-0.3
0.8
1.9
2.4
2.6
0.5
1.4
2.6
3.7
4.3
4.6
-0.3
1.1
2.5
3.8
4.4
4.8
-0.4
1.0
2.1
2.7
3.1
-2.0
-1.7
-1.5
-0.5
0.2
0.5
-2.0
-2.3
-3.8
-2.4
-1.3
-0.8
-2.1
-2.3
-3.1
-2.0
-0.8
-0.4
-0.2
-1.9
-2.6
-1.3
0.0
0.4
0.4
-1.8
-2.8
-1.5
0-0
0.4
e,
cmVcm3
.236
.228
.221
.210
.199
.189
.232
.225
.219
.214
.211
.209
.237
.225
.218
.214
.212
.211
.249
.239
.232
.227
.225
.224
.257
.251
.248
.247
.246
.267
.270
.269
.270
.268
.268
.266
.264
.264
.263
.263
.263
.256
.258
.255
.254
.253
.253
.243
.247
.243
.240
.237
.236
.239
.247
.248
.249
.245
.245
K,
mm/ da
1.21
0.48
0.33
0.24
0.18
0.11
3.91
1.35
0.75
0.38
0.24
0.14
15.89
4.29
1.74
0.76
0.43
0.23
59.72
15.06
3.62
1.43
0.89
0.47
18.29
21.61
14.56
4.76
4.57
30.96
15.24
-
8.76
5.88
5.25
27.38
13.09
6.65
2.67
1.19
0.63
13.67
7.47
4.34
1.02
0-85
0.60
19.69
9.41
9.16
1.95
1.09
0.55
6.02
11.43
7.63
2.03
1 .60
1.10
66
-------
TABLE 12. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND, KNOX COUNTY,
TEXAS, DURING SEPTEMBER 21 TO OCTOBER 5, 1973, LOCATION 3
Depth ,
cm
15
46
76
107
137
168
198
229
259
290
Particle size,
%
Sand 82
Silt 7
Clay 11
Sand 80
Silt 8
Clay 12
Sand 70
Silt 13
Clay 17
Sand 62
Silt 15
Clay 23
Sand 57
Silt 15
Clay 28
Sand 43
Silt 23
Clay 34
Sand 35
Silt 28
Clay 37
Sand 37
Silt 28
Clay 35
Sand 43
Silt 27
Clay 30
Sand 46
Silt 25
Clay 29
Bulk density,
g/cm3
1.49
1.39
1.36
1.52
1.67
1.73
1.71
1.63
1.56
1.65
Time,
da
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
0.6
1.5
4.0
9.0
15.0
Matric suction>
cb
-1.4
0..0
2.8
4.9
5.5
-3.1
-1.1
1.8
3.0
3.4
-2.3
-0.8
1.2
2.0
2.3
-1.6
-0.9
-1.5
1.7
1.6
-0.4
-4.1
-3.7
-2.0
0.9
-5.0
-5.8
-6.1
-5.1
-3.1
-2.5
-3.9
-3.7
-3.2
-2.3
-1.7
-3.1
-3.0
-1.8
1.0
-2.5
-2.8
-2.5
-1.2
-0.5
-1.7
-1.8
-1.8
-0.5
0.5
9,
cm3/cm3
.228
.220
.209
.196
.187
.245
.227
.217
.211
.208
.271
.249
.240
.234
.232
.275
.271
.267
.265
.263
.285
.284
.285
.285
.283
.277
.277
.277
.275
.278
.264
.264
.259
.260
.258
.264
.264
.259
.258
.256
.265
.252
.246
.243
.240
.284
.272
.264
.262
.259
K =
mm/da
34.54
13.01
18.06
30.48
18.62
188.98
54.86
37.26
50.80
32.18
241.38
39.24
11.15
4.62
2.79
613.21
212.47
0.00
0.00
134.62
-517.80
-12.62
-3.31
-0.91
-4.95
29.13
5.34
1 .20
0.40
-0.33
31.07
7.39
1.39
0.42
-0.34
101.21
12.69
3.43
1.04
-0.56
50.63
7.49
2.32
0.54
-0.32
32.83
13.11
4.05
1.12
0.32
67
-------
TABLE 13. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND, KNOX COUNTY, TEXAS, DURING AUGUST 7 TO SEPTEMBER 6,
LOCATION 1
1974,
cr>
00
Depth,
cm
15
Particle
Sand
Silt
Clay
size,
86
6
8
Bulk~~3ensity, Time,
q/cm3 da
1.55 0
0
2
5
10
15
.3
.8
.0
.0
.0
.0
20.0
46
76
107
Sand
Silt
Clay
Sand
Silt
Clay
Sand
Silt
Clay
82
7
11
74
9
17
71
10
19
1.52 0
0
2
5
10
15
20
1.53 0
0
2
5
10
15
20
1.56 0
0
2
5
10
.3
.8
.0
.0
.0
.0
.0
.3
.8
.0
.0
.0
.0
.0
.3
.8
.0
.0
.0
15.0
137
168
Sand
Silt
Clay
Sand
Silt
Clay
72
n
17
72
11
17
20
1.55 0
0
2
5
10
15
20
'1.56 0
0
2
5
10
15
20
.0
.3
.8
.0
.0
.0
.0
.0
.3
.8
.0
.0
.0
.0
.0
Matric suction,
cb
3.
4.
5.
7.
9.
n.
13.
1.
2.
3.
4.
6.
6.
7.
1.
2.
3.
4.
6.
6.
7.
1.
3.
4.
6.
8.
9.
9.
1.
3.
5.
7.
6
7
7
3
6
6
3
4
4
2
5
0
9
6
5
4
7
6
1
9
5
7
1
4
5
6
2
5
9
9
5
7
10.0
10.
10.
1.
3.
4.
6.
8.
9.
9.
6
7
4
3
8
7
4
3
7
e,
cm3/cra3
.231
.216
.198
.173
.145
.131
.127
.254
.248
.242
.236
.230
.225
.222
.248
.242
.237
.231
.227
.224
.222
.236
.224
.212
.203
.196
.192
.188
.228
.217
.208
.199
.192
.187
.183
.247
.232
.219
.206
.197
.191
.186
mm/ da
8.13
5.49
3.32
3.16
4.02
2.38
0.91
15.44
9.88
5.27
4.62
5.85
4.94
2.38
11.80
5.79
2.37
1.11
1.07
0.26
0.11
30.76
12.07
4.69
1.57
0.84
0.44
0.29
25.97
11.40
4.92
2.13
1.54
0.69
0.38
142.75
75.40
54.76
23.68
4.22
2.37
8.60
continued
-------
TABLE 13. (continued)
Depth ,
cm
198
229
259
290
320
Particle size,
%
Sand 71
Silt 13
Clay 16
Sand 69
Silt 11
Clay 20
Sand 66
Silt 11
Clay 23
Sand 67
Silt 12
Clay 21
Sand 69
Silt 12
Clay 19
Bulk density, Time,
g/cm3 da
1.60 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.64 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.68 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.72 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.73 0.3
0.8
2.0
5.0
10.0
15.0
20.0
Matnc suction,
cb
-1.4
0.0
1.4
3.1
4.9
6.2
7.0
-3.2
-1.7
0.0
2.4
4.5
5.9
6.7
-3.1
-1.1
1.2
4.6
6.2
7.5
8.0
-2.0
-1.1
1.2
4.1
6.2
7.5
8.0
-1.0
0.5
2.2
4.8
7.6
9.1
9.7
6,
an3/cm3
.263
.256
.247
.236
.230
.227
.225
.271
.268
.264
.260
.257
.254
.252
.260
.255
.258
.240
.235
.233
.230
.248
.240
.231
.222
.216
.213
.210
.248
.239
.232
.224
.218
.216
.214
K,
mm/ da
141.51
85.88
20.12
6.11
4.56
2.60
8.96
149.39
91.06
6.92
6.52
4.85
2.77
0.56
55.65
22.79
10.99
4.96
2.38
1.16
0.66
39.92
25.22
11.47
4.76
2.13
1.31
0.74
43.95
27.73
12.50
5.23
2.24
1.33
0.77
-------
TABLE 14. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND, KNOX COUNTY, TEXAS, DURING AUGUST 7 TO SEPTEMBER 6, 1974,
LOCATION 2
OeptlT,
cm
15
46
76
107
137
168
Particle size, Bulk density,
% g/cm3
Sand 85 1.49
Silt 6
Clay 9
Sand 81 1.45
Silt 8
Clay 11
Sand 74 1.42
Silt 12
Clay 14
Sand 68 1.45
Silt 15
Clay 17
Sand 66 1 .52
Silt 15
Clay 19
Sand 57 1.65
Silt 18
Clay 25
Time,
da
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
Matric suction,
cb
2.3
3.3
4.3
6.2
9.0
11.4
13.4
1.3
2.5
3.5
5.1
6.3
6.6
6.8
2.3
3.3
4.2
5.4
6.3
6.6
6.8
0.6
1.4
2.3
3.7
4.8
5.2
5.4
-1.1
0.1
0.7
1.7
2.7
3.2
3.6
-0.6
0.0
0.0
0.8
1.4
1.6
1.8
6,
cm3/cm3
.243
.237
.227
.205
.175
.151
.137
.233
.227
.227
.216
.209
.205
.202
.238
.231
.223
.216
.212
.210
.209
.256
.249
.241
.233
.229
.227
.226
.263
.260
.256
.251
.249
.248
.248
.268
.268
.268
.268
.269
.269
.268
,- , -—- r>—
mm/ da
1 .22
0.74
0.63
0.72
1.10
1.16
1.28
3.52
1.79
1 .14
1 .09
1.50
1.52
1 .89
32.92
16.79
6.86
2.62
1.71
1.52
1.07
55.83
39.56
29.35
29.83
2.80
1.83
0.85
36.84
13.77
6.78
4.68
4.34
5.64
3.57
18.87
13.21
13.67
4.55
2.16
1.42
1.25
continued
-------
TABLE 14. (continued)
Depth,
cm
198
229
259
290
320
Particle size,
%
Sand 50
Silt 21
Clay 29
Sand 45
Silt 24
Clay 31
Sand 44
Silt 26
Clay 30
Sand 50
Silt 24
Clay 26
Sand 52
Silt 22
Clay 26
Bulk density, Time,
g/cm3 da
1.74 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.71 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.62 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.60 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.64 0.3
0.8
2.0
5.0
10.0
15.0
20.0
Ma trie suction
cb
-0.8
-0.9
-1.2
-0.2
0.7
0.9
1.0
-3.7
-3.6
-3.3
-2.2
-1.0
-0.4
-0.2
-3.1
-2.6
-2.0
-1.1
-0.1
0.6
0.8
-1.8
-1.3
-0.7
0.3
1.3
1.8
1.9
-2.9
-2.6
-1.9
-0.7
0.4
1.8
1.0
65
cm3/cm3
.261
.261
.261
.261
.261
.261
.261
.256
.256
.255
.255
.255
.255
.253
.252
.248
.242
.237
.234
.234
.234
.259
.255
.252
.249
.247
.247
.246
.288
.285
.281
.277
.275
.275
.275
K,
mm/da
1379.22
264.03
14.86
9.25
3.53
1.88
1.30
75.82
21.13
12.27
4.75
2.85
1 .80
1.45
13.11
4.72
2.06
1.12
0.69
0.48
0.40
149.96
176.17
43.97
13.82
3.51
2.85
2.31
158.50
193.37
48.54
16.51
3.75
3.00
2.39
-------
TABLE 15. HYDRAULIC CONDUCTIVITY DATA AND VALUES OBTAINED FOR A MILES LOAMY FINE SAND, KNOX COUNTY, TEXAS, DURING AUGUST 7 TO SEPTEMBER 6, 1974,
LOCATION 3
--J
ro
Depth,
cm
15
46
76
107
137
168
Particle size, Bulk density,
% q/cm3
Sand 82 1.49
Silt 7
Clay 11
Sand 80 1.39
Silt 8
Clay 12
Sand 70 1 .36
Silt 13
Clay 17
Sand 62 1 .52
Silt 15
Clay 23
Sand 57 1 .67
Silt 15
Clay 28
Sand 43 1 .73
Silt 23
Clay 34
Time,
da
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
0.3
0.8
2.0
5.0
10.0
15.0
20.0
Matric suction,
cb
3.2
4.8
5.9
6.2
8.7
9.9
10.8
1 .1
2.8
3.9
5.1
6.1
6.8
7.4
1.5
2.7
3.7
4.1
5.1
5.3
5.4
-0.1
1.1
1.7
2.7
3.0
3.1
3.2
-1.5
0.1
-0.1
0.7
-0.9
0.7
1.1
-1.9
-1.1
-1.4
-0.7
-2.6
-1.0
-0.4
8,
cm3/cm3
.238
.234
.226
.211
.191
.174
.162
.253
.243
.233
.224
.217
.212
.213
.271
.263
.254
.249
.246
.244
.243
.272
.270
.269
.271
.270
.270
.269
.279
.279
.280
.278
.280
.281
.283
.274
.272
.272
.273
.273
.274
.273
T,"
mm/ da
1 .13
0.65
0.56
0.46
0.47
0.59
0.55
6.39
2.91
1 .47
0.86
0.76
0.96
0.91
35.05
53.03
14.20
9.23
5.94
3.23
3.29
69.12
18.90
513.08
12.31
-1.75
-8.69
-6.10
23.52
14.12
43.69
5.15
2.67
7.81
1.34
14.10
10.67
6.50
2.75
0.67
0.54
0.00
continued
-------
TABLE 15. (continued)
Depth
cm
198
229
259
290
320
Particle size,
%
Sand 35
Silt 28
Clay 37
Sand 37
Silt 28
Clay 35
Sand 43
Silt 27
Clay 30
Sand 46
Silt 25
Clay 29
Sand 44
Silt 26
Clay 30
Bulk density, Time,
g/cm3 da
1.71 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.63 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.56 0.3
0.8
2.0
5.0
10.0
15.0
20.0
1.65 0.3
0.8
2.0
5.0
10.0
15,0
20.0
1.75 0.3
0.8
2.0
5.0
10.0
15.0
20.0
Matric suction,
cb
-0.6
-1.3
-1.3
-0.4
-0.7
-0.4
-0.4
-0.1
-0.5
-0.1
0.7
0.8
1.1
1.1
-1.3
-0.7
-0.1
0.7
1.4
2.0
2.3
-1.1
-0.7
-0.3
0.5
1.4
2.0
2.4
-0.4
-0.2
0.2
1.0
1.8
2.4
2.8
8
cm3/cm3
.266
.266
.266
.267
.268
.266
.266
.259
.257
.255
.252
.252
.252
.252
.258
.253
.249
.245
.242
.240
.239
.276
.272
.269
.265
.263
.262
.262
.279
.278
.277
.275
.273
.272
.270
K,
mm/ da
17.84
7.77
6.87
1 .86
0.53
0.52
0.00
30.87
9.61
9.13
2.28
0.66
0.59
0.53
39.96
18.15
18.53
6.25
1.51
1.33
0.93
23,90
11.34
9.21
2.71
0.94
0.75
0.70
29.32
13.88
10.46
3.21
1.12
0.89
0.82
-------
200
TOO
80
60
r-
• -
x -
A
A-
n -
DEPTH,
cm
76
107
137
168
CLAY,
%
17
19
17
17
SAND,
%
74
71
72
72
BULK
DENSITY
1.53
1.56
1.55
1.56
40
20
I 10
---. o
^ 6
»s
H- A
i—i t
>
i—i
I—
1 2
o
o
I—I
—1 ,
g 0.8
= 0.6
0-4
0.2
0.1
0.08-
0.06-
0.04
18
Figure 24.
LOCATION 1,
TEST 2
0-
®-
©-
0>-
DEPTH,
cm
198
229
259
290
CLAY,
%
16
20
23
21
SAND,
%
71
69
66
67
BULK
DENSITY
1-60
1.64
1.68
1.72
20
26
28
22 24
SOIL-WATER CONTENT, volume %
Hydraulic conductivity vs soil-water content for various depths
in a Miles loamy fine sand in Knox County, Texas, 1973.
74
-------
O
O
CJ
200
100 -
80 -
60
40
20
10
8
6
4
L A- 229 cm T2 August 7 to September 6, 1973
1
0.8
2 0.6
Q
0.4
0.2
0.1
0.08
0.06
0.04
22
D - 76 cm TQ September 8 to October 3, 1973
O - 76 cm TI October 8 to October 29, 1973
A- 76 cm T2 August 7 to September 6, 1974
• - 229 cm Tj September 21 to October 5, 1973
LOCATION 1
23
24 25
SOIL-WATER CONTENT, volume
26
27
Fiqure 25 Hydraulic conductivity vs soil-water content at different times
for the 76- and 229-cm depths in a Miles loamy fine sand.
75
-------
-3.0
Figure 26.
n - 76 cm TQ September 8 to October 3, 1973
O- 76 cm TI October 8 to October 29, 1973
A- 76 cm T2 August 7 to September 6, 1974
• - 229 cm TI September 21 to October 5, 1973
A- 229 cm T, August 7 to September 6, 1973
LOCATION 1
-2.0 -1.0
7.0 7.5
1.0 2.0 3.0 4.0
MATRIC SUCTION, -cb
Hydraulic conductivity vs matric suction at different times
for the 76- and 229-cm depths in a Miles loamy fine sand.
76
-------
Another problem encountered in determining hydraulic conductivity was
relative to the uneven pressure gradients. In Figure 27, negative hydraulic
gradients were nonexistent at some measurement dates (0.6, 1.5, 4 and 9 days)
for some depths (101.6 to 152.4 cm). The lack of gradients at these depths
indicates that water moved through succeeding layers of the soil profile due
to a pressure head rather than a pressure gradient. Overall, the pressure
gradient was approximately 1 or greater after 15 days at 304.8 cm even with
the existence of the pressure head at 101.6 to 152.4 cm.
304.8-
254.0
o
CM
o
Q
-------
It was not an objective of this project to develop a classical model
for this soil type. With the problems described previously, it can be seen
that such an undertaking would be a major project by itself. However, it
was decided to develop a statistical model to evaluate hydraulic conduc-
tivity as a function of easily measurable variables using a stepwise regres-
sion analysis. The following soil characteristics were considered and
measurements were made for 124 sets of data cases:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
(cm/da);
soil in
Field
Upper
above
Location (Plot 1, 2 or 3).
Experiment number (1 or 2).
Observed hydraulic conductivity [centimeters per day
6 - soil-water content (volume fraction) of layer of
question.
Upper 6 - soil-water content of the layer of soil 30 cm above the
layer of soil in question.
Lower 6 - soil-water content of the layer of soil 30 cm below the
layer of soil in question.
capacity - 8 of soil after 12 to 18 days.
field capacity - field capacity of the layer of soil 30 cm
the layer of soil in question.
Lower field capacity - field capacity of the layer of soil 30 cm
below the layer of soil in question.
Bulk Density - ratio of weight of volume of soil to weight of
equal volume of water.
Matric Suction - soil-water potential (cb).
Time - time at which all measurements were made after application
of water to soil.
Depth - depth (cm) of soil at which all measurements were made.
Percent Sand.
Percent Silt.
Percent Clay.
Upper Sand - percent sand
of soil in question.
Silt - percent silt
of soil in question.
Clay - percent clay
of soil in question,
Sand - percent sand
of soil in question,
Silt - percent silt
of soil in question,
Clay - percent clay
layer
Upper
layer
Upper
layer
Lower
layer
Lower
layer
Lower
layer
of soil in question.
of the layer of soil 30 cm above the
of the layer of soil 30 cm above the
of the layer of soil 30 cm above the
of the layer of soil 30 cm below the
of the layer of soil 30 cm below the
of the layer of soil 30 cm below the
From the original list of variables, field capacities, matric suction,
and time were deleted because it was decided that these variables were
difficult to measure or use. Then, many combinations of the remaining
variables were introduced into the program. Numerous possible ratios,
crossproducts, natural logs, square roots, squares, and cubes were used
(some 250 combinations in all). From these combinations, the program
selected those terms which best explained the variation in the dependent
78
-------
variable, natural log of the hydraulic conductivity. The model evolved is
as follows:
Natural Log of Hydraulic Conductivity (K) = [8]
-.00372 x Lower Sand x Lower 9 - 4.99338 x Natural Log of Clay
-34.50021 x *T + 130.24553 x r^-^
uepth Upper Sand
* - 27.00883
-38.45392 x - .47643 x Upper Silt
-29 06143 x Lower 9 + a 7RR98 Y Lower 6
^y.Ub!4J X + 8.75828 x
-15.60952 x + 104.16374 (constant)
R2 = .8368 R = .9148
Natural log of standard error of estimate = 1.7214
Standard error of estimate = 5.5921 cm/da
Natural log of mean hydraulic conductivity = -1.5683
Mean hydraulic conductivity = 0.2084 cm/da
It should be understood that this model is a statistical model only and
in no way describes the relationship between the variables.
Cl i mate ( I ncl ud i ng Ra i nf a 1 1 )
The method by Jensen, et al . (10) was used to calculate potential ET.
Since the model involves maximum and minimum temperatures and relative
humidities, wind run, and solar radiation, the ET potential obtained is an
expression of all the parameters measured. Figure 28 shows the cumulative
ET potentials obtained for the growing season of the first crop grown during
each of the four years of the study along with the rainfall received during
each of the growing seasons. It can be seen that the ET potential varied
from 483.3 to 596.2 mm for a difference of 112.9 mm and that the rainfall
during the growing season varied from 104.3 to 224.7 mm for a difference of
120.4 mm. Thus, the ET potential and rainfall for a given cropping season
each varied over 100 mm. Sweet corn is one of the shorter season crops
79
-------
00
o
ET
potential, Rainfall,
mm mm
14 29
JUNE
14 29
JULY
13 28
AUGUST
12 27
SEPTEMBER
Figure 28. Cumulative ET potential following emergence of the first corn crop planted 1971-1974.
-------
grown in the area, and larger variations could be expected for crops such as
cotton, wheat, and grain sorghum which have considerably longer qrowinq
seasons. 3 3
This variation emphasizes the fallacy of irrigating crops on stage of
growth. To minimize irrigation return flows from cropping systems in the
area, it. will be necessary to have a budgeting system involving the evapora-
tive demand of the atmosphere, rainfall, crop water requirement, and water-
holding capacity of the soil.
As the evaporative demand of the atmosphere and the rainfall have been
discussed in this section, this leaves only the water demand of the crop.
Ritchie (21) has pointed out that the water requirement of cotton and grain
sorghum is related to the leaf area until the crop reaches a LAI of approxi-
mately 2,7. To determine if his finding is also true for the sweet corn
used in the study, it was necessary to find a simplified method of determin-
ing LAI for the crop. Relationships between leaf area and stem diameter
were derived as follows:
Log y = -1.169 + 2.389 Log x r = .954 [9]
J~J~ = -22.872 + 7.337 /IT r = .952 [10]
where y = leaf area,
x = stem diameter 2.54 cm above the ground.
By multiplying the area of each individual plant times the plants per
unit area and dividing by the area involved, it was possible to determine
the LAI.
Another factor with respect to rainfall that should be mentioned is the
amount of rainfall received during the year while a crop was not growing.
Table 16 shows the rainfall by months, the total received, and the amount
received with and without a crop during the years of the study. It can be
seen that 417.9 to 518.7 mm rain was received while the area was without a
crop. This amount is two to four times that received during the growing
season and emphasizes the need to develop management practices to either
exhaust all the potential pollutants such as nitrates through precision
fertilization practices or grow crops for longer periods during the year
to absorb any nitrates that might be available to be leached due to
additions of excess rainfall or irrigation water.
Sampling
Soil-Water Extraction System--
Problems existed throughout the study with the soil-water extraction
system. During the first year of the study, the 0.64-cm O.D. vacuum line
had to be replaced with 1.27-cm O.D. line in order to obtain adequate
vacuum for the soil-water extraction tubes. Even after the vacuum line
was replaced, it was not possible to obtain samples from all extraction
tubes.
81
-------
TABLE 16. MONTHLY RAINFALL RECEIVED AT THE FIRST FIELD SITE,
KNOX COUNTY, TEXAS, 1971-1974
1971 1972 1973 1974
mm
January
February
March
April
May
June
July
August
September
October
November
December
Total
With crop
Without crop
152.4
14.0
70.1
153.2
74.9
201.4
15.2
41.9
723.1
224.7
498.4
3.8
10.2
2.5
11.4
94.2
69.1
71.9
126.5
106.7
208.8
18.0
-
723.1
204.4
518.7
57.2
43.4
82.0
56.9
19.6
52.6
69.1
17.8
166.9
33.0
20.1
-
618.5
104.3
514.2
8.6
6.4
25.4
56.4
34.3
80.3
4.3
35.6
170.2
143.5
10.2
35.6
610.6
192.7
417.9
As the season progressed, the number of soil-water samples extracted
from the profile increased. This was probably due to better contact between
the soil and soil-water extraction tubes and the soil-water content increas-
ing at the lower depths to a point that adequate water was available for
extraction. A high level of soil-water content was required in order to
obtain samples of adequate size due to the high sand content of the soil.
Most soil-water movement apparently ceased within a short period of time
after water applications due to the high sand content of the soil. It was
determined that the best procedure for obtaining samples was to begin
extraction 24 hours following water additions and extract for a 48-hour
period. The percentage of tubes from which extracts could be taken
increased each year of the study. One of the problems in extracting the
soil-water samples was the evaporation of the samples after they entered
the extraction bottles. It was necessary to put mineral oil in each of the
bottles to prevent the sample from evaporating. With this change, the
concentrations of the ions in the water obtained from the water table and
that from the irrigation wells were approximately the same. Any deviation
of a large amount would have been noted between these two samples in that
they came from the same source.
After the second year of the study, the vacuum was concentrated on the
location in the plots with the deep extraction tubes. Some problems existed
with the system following the second year of the study. The underground
vacuum line had a considerable number of leaks. These occurred at insert
82
-------
tees that had cracked and insert male adapters that split due to weather
exposure. Many shallow soil-water sampling tubes were broken from cultiva-
tion practices after the 1972 crop was harvested. The small nylon lines
that connect the extraction tubes to the vacuum manifold had to be repaired
or replaced. Weather exposure caused these lines to become brittle and
break. During initial soil-water sampling, several deep extraction tubes
were found to be broken and required replacement.
After the third year of the study, it was decided that adequate soil-
water extract data had been obtained and that more effort should be expended
on soil samples. The number of soil-water samples obtained was therefore
decreased.
The dates on which samples were taken during the different years are
shown in Table 17. Appropriate data from the different dates will be
discussed under the results and discussion.
Comparison of Vacuum and Core Samples During 1971--
Due to the large number of soil-water extracts missing during the first
year and the question of soil-water extracts vs core samples, it was decided
to compare these two sampling methods. Comparisons were made between 1:1
extracts of core samples obtained at the beginning and end of the growing
season and porous bulb soil-water extracts obtained at the end of the grow-
ing season. All samples were analyzed for nitrate-nitrogen (nitrate-N),
chloride, sulfate, magnesium, ammonium, potassium, calcium, sodium, and
conductivity. Concentrations of nitrate-N were similar to a depth of 210 cm
for both sampling methods, but increased dramatically for vacuum samples
below this depth (Figure 29). Chloride concentrations were similar for both
systems down to 90 cm when vacuum sample concentrations again became much
greater than 1:1 soil-water extracts. The other anion measured, sulfate,
behaved differently in that concentration divergencies between sampling
systems occurred in the upper levels of the profile (0 to 180 cm) and
similar concentrations were measured at lower depths.
Concentrations of the divalent cations calcium and magnesium were
similar for the two sampling systems in the upper portions of the profile
(Figures 30 and 31). Conversely, for the monovalent cations potassium and
sodium, concentrations were different in the upper portions of the profile
and similar at lower depths. Ammonium concentrations were generally low
(<4 ppm) and too erratic for comparisons. As might be expected, conduc-
tivity was dissimilar for the two sampling systems throughout the profile.
A correction was made to place the 1:1 extract data on a field moisture
basis as follows:
1:1 extract concentration 10Q = field concentration [11]
% moisture of sample
However, in Figure 32, where the correction for variable water content was
made, this correction did not eliminate the differences between sampling
systems.
83
-------
TABLE 17.
Date
June 3
June 25
July 8
Aug. 2
Aug. 17
Sept. 3
Sept. 27
April 14
April 19
April 20
April 24
May 4
May 5
May 8
May 30
May 31
June 1
June 2
June 5
June 6
June 8
June 10
June 12
June 13
June 22
June 27
June 28
June 30
July 3
July 5
July 28
July 29
July 30
Aug. 14
Aug. 28
Aug. 31
Sept. 6
Sept. 13
Sept. 14
DATES ON WHICH SOIL-WATER EXTRACTS WERE OBTAINED FROM THE VARIOUS
Plot Numbers
1971 - 1st crop
1-39
1-39
1-39
1-39
1-39
1-39
1971 - 2nd crop
27, 38, 32, 33
1972 - 1st crop
14T26
40, 41
42, 43
37-39, 44, 45
1-13
27-39
14-26, 40-45
45
15, 19, 41
16-18, 20, 36-39
42
1-14, 27, 29, 31-35
30, 40, 43, 44
22-26, 36
4, 9, 14-18, 20
27, 28, 30, 31, 33, 35, 38, 39
5, 21, 36, 42
5-7, 10, 17-19, 21, 22-26, 31-33, 36, 40-45
8, 11-13
2, 15, 17, 21, 23-26
5-7, 31, 36, 40, 41
34, 44, 45
5.7, 10, 17-19, 21, 31-33, 36, 40-45
1972 - 2nd crop
6-8, 17-19, 33, 34
32
40-45
6-8, 17-19, 32-34, 40-45
6-8, 17-19, 32-34, 40-45
19
6-8, 17-19, 32-34, 40-45
40, 43
17, 34
PLOTS IN KNOX
Date
Sept. 19
Sept. 21
Oct. 2
Oct. 5
April 11
June 4
June 11
June 12
June 13
June 14
June 15
June 19
June 20
June 21
June 22
June 25
June 26
June 27
June 28
June 29
July 2
July 3
July 5
July 6
July 9
July 10
July 11
May 25
June 7
June 17
June 19
June 20
June 21
June 26
July 1
July 5
July 8
July 10
July 12
COUNTY, TEXAS, 1971-1974
Plot numbers
1972 - crop (continued)
7, 8, 33
6-8, 10, 17-19, 21, 32, 34, 36, 40-45
17, 34
6, 7, 19
1973
1-45
1-45
4, 8, 10, 14, 18, 19, 36
16, 20, 21
1, 2, 6, 7, 12, 13, 15, 17, 32, 34, 35, 37-39
22-26
3, 5, 9, 11 , 27-31, 33
14-16, 18, 19, 32, 35-39
1, 3, 4, 6-13, 34, 40, 43
20, 21, 29, 33
2, 5, 17, 22-28, 30, 31
41, 44
4, 6-11, 14-16, 18, 19, 21, 32, 34-37
2, 12, 13, 29, 38, 39
2, 5, 33
1, 4, 20, 30, 31, 36
17, 22-26
6-11, 14-16, 18, 19, 21, 27, 28, 32, 34-37
2, 12, 13, 29, 33, 38, 39
1, 3-5, 15, 20, 30, 31
41 , 43, 44
2, 6-11 , 29, 32, 34-36
12-14, 16-19, 21-26, 33, 37-39
1974
9, 20, 23, 24, 35
9, 20, 23, 24, 35
4, 24
20
35
23
9, 24
20
23
24, 35
9
8, 12, 13, 25, 26, 34, 38, 39
-------
CO
en
18.5
MATRIC
CLAY, POTENTIAL,
% cb
6 0
14
16
18
33
34
26.4 27
25.8 26
24.3 26
25.2 36
200
0
1
-2.0
2.1
-8.9
-2.9
-1.9
-16.9
-6.9
0 10 20 30 40 0 25 50 75 0 50 100 150
NITRATE-N, ppm CHLORIDE, ppm SULFATE, ppm
Figure 29. Concentrations of nitrate-N, chloride, and sulfate in a furrow-irrigated plot (Plot 20)
in 1:1 extracts of core samples at the beginning of the growing season (curve 1) and end
of growing season (curve 2) and in vacuum samples at the end of the growing season
(curve 3), 1971.
-------
00
cr>
MATRIC
CLAY, POTENTIAL,
cb
0
3.0
1 2 3 4
AMMONIUM, ppm
10 20 30 40 50
POTASSIUM, ppm
-2.0
2.1
-8.9
-2.9
-1.9
-16.9
-6.9
10 20 30 40 0
MAGNESIUM, ppm
Figure 30. Concentrations of magnesium, ammonium, and potassium in a furrow-irrigated plot (Plot 20)
in 1:1 extracts of core samples at the beginning of the growing season (curve 1) and end
of growing season (curve 2) and in vacuum samples at the end of the growing season
(curve 3), 1971.
-------
00
—I
0.0
3.0
Figure 31.
18.5
MATRIC
CLAY, POTENTIAL,
% cb
24.8 14
20.7 16
23.8 18
5.6 33
27.2 34
26.4 27
25.8 26
24.3 26
25.2 36
0
250 500 750 1000
CONDUCTIVITY, u mhos
0
-2.0
2.1
-8.9
-2.9
-1.9
-16.9
-6.9
25 50 75 0 25 50 75
CALCIUM, ppm SODIUM, ppm
Concentrations of calcium, sodium, and conductivity in a furrow-irrigated plot (Plot 20)
in 1:1 extracts of core samples at the beginning of the growing season (curve 1) and end
of growing season (curve 2) and in vacuum samples at the end of the growing season
(curve 3), 1971.
-------
CLAY,
3.0
Figure 32.
6
14
16
18
33
34
27
26
A - VACUUM SAMPLES 26
o - CORE SAMPLES
26
40 60
NITRATE-N, ppm
80
36
Comparison of nitrate-N concentrations of vacuum soil-
water samples and 1:1 extracts of soil samples for
various depths, Plot 20, Location 1. Field site near
Munday, Texas, 1971.
Peak ion concentrations measured in the vacuum extract are somewhat
related to soil characteristics. Both the 1.2- and 2.7-m concentration
peaks of most of the ions are immediately above clay layers and are in
zones of low matric potential. The presence of peak anion concentrations
in the soil solution at these depths indicates poor leaching from the
layers. These data indicate that 1:1 extracts may not adequately represent
ion concentrations in the field as affected by soil physical conditions.
88
-------
Kissel (11) has published relative to the small pore and large pore
leachate. If his work can be extrapolated to these coarser-textured soils,
it might be possible that the soil-water extracts give an index as to that
portion of the soil solution in the large pores in which most of the ion
movement takes place. This portion of the soil solution may in no way be
representative of the bulk solution and may involve only a small portion of
the soil water. However, this may be the dynamic portion of the soil water
which contributes to degrading the quality of irrigation return flows.
The bulk solution is apparently less dynamic but is more representative
of the toal salts in the soil. Leaching is apparently slower in bulk
solution than in the vacuum-sampled solution.
Due to the major differences obtained, it was decided to further com-
pare the vacuum and core studies in 1972. The results of these studies
follow.
Comparison of Vacuum and Core Samples During 1972--
Sampling during the growing season—In 1971, some questions remained
unanswered following the comparison of vacuum and core samples. In 1972,
sprinkler-irrigated (Plot 10), furrow-irrigated (Plot 21), and subirrigated
(Plot 36) plots were simultaneously core-sampled and vacuum-sampled at
various times during the growing season. The objectives of the study were
to compare the sampling techniques as indicators of ion movement and evalu-
ate the possibility of using bromide as an indicator of nitrate movement.
Bromide was chosen because of its low toxicity to plants and low concen-
tration in soil and irrigation water.
Vacuum was used to extract samples through porous bulbs located at
various depths beneath the tops of the beds in two locations of each plot.
For comparison purposes, 2.5-cm diameter core samples were also taken in
15-cm increments from the tops of adjacent beds to depths of 300 cm.
After initial sampling to determine background concentrations of
nitrate-N, bromide and chloride, granular sodium nitrate and sodium bromide
were mixed and chiseled into the sides of the beds (25 cm from the center of
each bed) at nitrogen and bromide rates of 45 and 54 kg/ha, respectively.
Sweet corn was planted.
Porous bulb samples and core samples were taken simultaneously after
each rainfall or irrigation throughout the crop year. Moisture content of
core samples was determined; and the samples were ground, extracted with
equal weights of deionized water, and filtered through a pressure filtration
apparatus. Ion concentrations of the 1:1 soil:water extracts were divided
by the air-dry moisture percentages.
Samples taken prior to the bromide and nitrate applications showed that
the bromide and nitrate applications were low. Bromide concentrations from
core samples varied from 0.06 to 0.55 ppm, and porous bulb samples 0.4 to
3 5 ppm Nitrate-N concentrations were somewhat higher in that the ranges
for core samples and porous bulb samples were 0.6 to 6.4 ppm and
89
-------
4 to 33 ppm, respectively. A discussion of the results from each irrigation
system follows.
Sprinkler-irrigated plots--Data from the porous bulb samples were much
more consistent than that of the cores. Bromide and nitrate-N data from the
soil-water extracts prior to the bromide application and during the growing
season are shown in Figure 33. It can be seen that the bromide peak was
detected at 0.3, 0.9 and 1.2 m, respectively, 14, 35 and 47 days after
bromide and nitrate applications.
The nitrate-N concentrations prior to nitrate and bromide applications
and 14 days after application were approximately equal at 0.3 and 0.6 m and
were not related to the bromide concentrations indicating the nitrate was
from soil nitrogen. The nitrate-N concentrations decreased at 0.3 and 0.6 m
35 days after application and further decreased at 0.9 m 47 days after
application but increased at 1.2 and 1.5 m. The bromide moved from 0.3 to
1.2 m during the course of the growing season due to the addition of rain-
fall and irrigation water. Nitrate, on the other hand, decreased between
0 and 0.9 m due to crop utilization but increased at 1.2 and 1.5 m due to
leaching. The peaks for bromide and nitrate below 0.6 m were qualitatively
related.
The only date in which the bromide and nitrate-N concentrations of core
samples were higher than those obtained prior to bromide and nitrate appli-
cations was 35 days after application (Figure 34). Bromide and nitrate-N
concentration peaks occurred at 0.6 m in the core samples (Figure 34) com-
pared to the peaks at 0.9 m of the vacuum samples (Figure 33). This
suggests the sample obtained through the porous bulbs may have been obtained
from a large area which included ions from the 0.6-m zone. Another possi-
bility is that the movement in the row with the porous bulbs was different
from the row from which the core samples were obtained.
Furrow-irrigated plots--The data from the furrow-irrigated plots were
unique in two respects. The bromide and nitrate-N concentrations were
higher than from the other two irrigation systems. Further, there was
closer qualitative agreement between the core and vacuum samples. Figure 35
shows the vacuum bromide and nitrate-N concentrations. The data obtained
after bromide and nitrate applications show good qualitative correlation
between bromide and nitrate. Peak concentrations did not occur below 0.9 m
while they were at 1.2 m in the sprinkler-irrigated plots (Figure 33). Ion
concentrations of the core samples as the season progressed are given in
Figure 36. The same qualitative relationships existed as were found with
the vacuum samples, but the relative concentrations were not as high.
Subirrigated plots—Neither the bromide nor nitrate-N concentrations
were very high in the subirrigated plots throughout the growing season. In
only two of the measurements did the bromide concentrations obtained during
the growing season exceed the concentrations obtained prior to the applica-
tion of the bromide. These data are shown in Figure 37. It can be seen
that peak concentrations of bromide in the vacuum extracts occurred at 0.6 m
at 25 and 42 days after application and at 1.2 and 0.9 m, respectively, in
90
-------
D_
LU
Q
0.0
0.3
0.6
0.9
1.2
\
1.5
1.8
2.1
2.4
2.7
3.0
CURVE NO.
1
2
3
4
DATE
PRIOR TO BROMIDE &
NITRATE APPLICATION
14 DAYS AFTER BROMIDE &
NITRATE APPLICATION
35 DAYS AFTER BROMIDE &
NITRATE APPLICATION
47 DAYS AFTER BROMIDE &
NITRATE APPLICATION
1 2
0
20 40
BROMIDE, ppm
60
20 40 60
NITRATE-N, ppm
80
Figure 33. Concentrations of bromide and nitrate-N in porous bulb soil-water extracts obtained
from the sprinkler-irrigated plots, 1972.
-------
ro
DATE
PRIOR TO BROMIDE &
NITRATE APPLICATION
35 DAYS AFTER BROMIDE &
NITRATE APPLICATION
5 10
BROMIDE, ppm
15
5 10 15
NITRATE-N, ppm
20
Figure 34. Concentrations of bromide and nitrate-N in 1:1 extracts of core samples obtained from
the sprinkler-irrigated plots, 1972.
-------
CO
CL.
U-l
Q
0.0
0.3
0.6
0.9i
1.2
1.5
1.8
2.1
2.4
2.7
3.0
CURVE NO.
1
3
4
DATE
PRIOR TO BROMIDE &
NITRATE APPLICATION
17 DAYS AFTER BROMIDE &
NITRATE APPLICATION
25 DAYS AFTER BROMIDE &
NITRATE APPLICATION
47 DAYS AFTER BROMIDE &
NITRATE APPLICATION
25 50
BROMIDE, ppm
75
25 50 75
NITRATE-N, ppm
100
Figure 35. Concentrations of bromide and nitrate-N in porous bulb soil-water extracts from the
furrow-irrigated plots, 1972.
-------
1.2
1.5
Q_
UJ
Q
1.8
CURVE NO. DATE
1 PRIOR TO BROMIDE AND
NITRATE APPLICATION
2 17 DAYS AFTER BROMIDE &
NITRATE APPLICATION
3 25 DAYS AFTER BROMIDE &
NITRATE APPLICATION
4 47 DAYS AFTER BROMIDE &
NITRATE APPLICATION
10 20
BROMIDE, ppm
30
25 50
NITRATE-N, ppm
75
100
Figure 36. Concentrations of bromide and nitrate-N in 1:1 extracts of core samples obtained from
the furrow-irrigated plots, 1972.
-------
VO
en
a.
yj
Q
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
SOIL WATER EXTRACTS
0
Figure 37.
DATE
PRIOR TO BROMIDE &
NITRATE APPLICATION
15 DAYS AFTER BROMIDE
& NITRATE APPLICATION
25 DAYS AFTER BROMIDE
& NITRATE APPLICATION
42 DAYS AFTER BROMIDE
& NITRATE APPLICATION
CORE SAMPLES
10 20
BROMIDE, ppm
30
1 2
BROMIDE, ppm
Concentration of bromide in porous bulb soil-water extracts and 1:1 extracts of core
samples obtained from the subirrigated plots, 1972.
-------
the core samples so there was little agreement between the core samples and
soil-water extracts. This is probably due to the fact that different beds
were used for soil-water extracts and core samples, and more variation as
water movement occurred under the subirrigation system.
In no case was the nitrate-N content of either the soil-water extracts
or the cores higher than those obtained prior to fertilizer application.
Thus, nitrates were not detected with either sampling method.
Chloride concentrations in all systems—Chloride concentrations in the
vacuum samples at the beginning and later in the growing season are shown in
Figure 38 along with the chloride concentration of the irrigation water.
Concentrations higher than those in the irrigation water were found in the
surface 0.9 m and tended to increase as the season progressed. This was
probably a result of concentration due to evaporation and leaching by rain-
fall. Concentrations were highest below 0.6 m in the furrow-irrigated plots
followed by the sprinkler-irrigated and subirrigated plots. This held true
throughout the growing season indicating that the quality of irrigation
return flows would be better from subirrigation systems than the other two
systems. The amounts of water applied in the sprinkler irrigation, furrow
irrigation, and subirrigation systems in this study were 21.59, 27.92, and
24.13 cm, respectively. Therefore, the differences in concentration were
probably due to the differences in water movement in the irrigation systems
rather than the amount of water applied. Chloride concentrations in the
surface 0.6 m were highest in the sprinkler-irrigated system followed by the
furrow and subirrigation systems.
Data obtained from the core samples at the beginning of the season and
toward the end of the growing season are shown in Figure 39. Major
increases in chloride occurred in the surface 0.9 m in the furrow and
sprinkler irrigation systems while only small changes occurred in the
subirrigation system. Concentrations below the root zone were generally
low (<10 ppm) which is too low to be of concern.
Sampling at the end of the growing season—Since major differences
occurred in the data obtained from the different irrigation systems during
the growing season, it was decided to obtain a detailed cross-section of
bromide, nitrate-N, and chloride concentrations at the end of the growing
season to determine the fate of bromide and nitrate bands applied to each
irrigation system.
Soil core samples 2.5 cm in diameter and 30 cm long were taken at 13-cm
intervals laterally from one bed to an adjacent bed (102 cm) to depths of
210 cm. Results are shown in Figures 41 through 46. The cross-sections
show the actual location of the bands of bromide and nitrate-N. Chloride
concentrations indicate the extent and location of the season's irrigation
water (see Key, Figure 40).
In Location 1 of the sprinkler-irrigated plot (Figure 41), bromide
was found as two distinct bands directly below the application sites in
the sides of the beds. Nitrate-N concentrations were low in the area of
96
-------
0.0:
0.3
0,6'
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
0
IRRIGATION WATER
^CONCENTRATION
77 ppm
1
FURROW
CURVE 1 - PRIOR
TO BROMIDE &
NITRATE
APPLICATION
CURVE 2-34
DAYS AFTER
BROMIDE &
NITRATE
APPLICATION
JRRIGATON WATER
CONCENTRATION
__77 ppm
2
SPRINKLER
CURVE 1 - PRIOR TO
BROMIDE &
NITRATE
APPLICATION
CURVE 2-40 DAYS
AFTER BROMIDE
& NITRATE
APPLICATION
IRRIGATION WATER
"CONCENTRATION
77 ppm
2
SUBIRRIGATED
CURVE 1 - PRIOR TO
BROMIDE &
NITRATE
APPLICATION
CURVE 2 - 45 DAYS
AFTER BROMIDE
& NITRATE
APPLICATION
150
300
150 300
CHLORIDE, ppm
150
300
400
Figure 38. Concentration of chloride in porous bulb soil-water extracts of samples
obtained from furrow, sprinkler, and subirrigated plots, 1972.
-------
CO
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
Figure 39.
FURROW
CURVE 1 - PRIOR
TO BROMIDE &
NITRATE
APPLICATION
CURVE 2-34 DAYS
AFTER BROMIDE
& NITRATE
APPLICATION
10 20 30
CHLORIDE, ppm
SPRINKLER
1 2
CURVE 1 - PRIOR
TO BROMIDE &
NITRATE
APPLICATION
CURVE 2-40 DAYS
AFTER BROMIDE
& NITRATE
APPLICATION
TO 26 3T0
CHLORIDE, ppm
SUBIRRIGATED
1 2
CURVE 1 - PRIOR TO
BROMIDE &
NITRATE
APPLICATION
CURVE 2-45 DAYS
AFTER BROMIDE
& NITRATE
APPLICATION
10 20 30
CHLORIDE, ppm
40
Concentrations of chloride in 1:1 extracts of core samples obtained from
the furrow, sprinkler, and subirrigated plots, 1972.
-------
(a) CHLORIDE
(>10 ppm)
(b) BROMIDE
(>1 ppm)
(c) NITRATE-N
(>5 ppm)
Figure 40. Symbol key for Figures 41 through 46.
99
-------
O.Or
0.3
0.6
0.9
Q.
S 1.2
1.5
1.8
2.1
_L
0 12.7 25.4 38.1 50.8 63.5 76.2 88.9 101.6
LATERAL DISTANCE, cm
Figure 41. Areas of significant concentrations of bromide,
nitrate-N, and chloride in a sprinkler-irrigated
plot (Plot 10-1) 81 days after application of
bromide, 1972. (See Figure 40 for symbol key)
A - Original location of fertilizer band.
100
-------
high bromide concentrations indicating that the nitrogen was used by the
crop when the bands were higher in the profile.
In the other sampling location of the sprinkler plot (Figure 42), the
bromide bands grew more diffuse as they moved downward to depths of 1.8 to
2.1 m. High nitrate-N concentrations were found within each bromide band,
indicating that the nitrogen bands were leached from the root zone before
they could be used by the crop.
The fertilizer bands, although still apparent, were much more diffuse
in the furrow-irrigated plots than in the sprinkler-irrigated plots
(Figures 43 and 44). Furrow-applied water moved material toward the beds
and down and maximum bromide and nitrate-N concentrations were found below
the tops of the beds in Location 1. Lateral movement of the bands over a
restricting layer is indicated in Location 2 of the furrow plot. Both
locations of the furrow plot indicated nitrate-N leaching losses.
Erratic results were obtained in Location 1 of the subirrigated plot
and were probably a function of the sampling location relative to the
emitters of the laterals (Figure 45). One fact is obvious: although there
were no restricting layers and water moved freely through the upper 2.5m
of the profile, subirrigation had kept applied nitrate-N and bromide in the
surface 0.9 to 1.2 m. A logical pattern of chloride accumulation around the
laterals of Location 2 (Figure 46) is apparent. Bromide was moved from the
point of application toward the furrow and was still located in the upper
0.75 m. As with the sprinkler system, when bromide was held in the surface
0.90 m, nitrate-N was not detected.
Summary and Conclusions--
The three different irrigation systems provided three distinct patterns
of irrigation water and fertilizer band movement (Figures 41 through 46):
1. Water applied through sprinkler systems and rain tends to move
the banded material straight down. Some of this may be
obtained by a vacuum system (Figure 33) but may be missed by
core sampling unless it diffuses into the center of the bed.
2. Furrow-applied irrigation water concentrates the bands in the
plane of the bulbs.
3. Subirrigation water concentrates the bands in the top of the
bed away from the porous bulbs. Water flow was radially
outward, carrying fertilizer salts away from the sampling
area in the root zone.
Cross-sectional core sampling, although much slower and more tedious,
proved to be a better method of sampling. Actual location and concentra-
tions of the bands were determined by this method in most cases, while
single-plane porous bulb samples indicated higher concentrations in the
root zones of furrow plots and lower concentrations in sprinkler and
subirrigated plots.
101
-------
0.0
0 12.7 25.4 38.1 50.8 63.5 76.2 88.9 101.6
LATERAL DISTANCE, cm
Figure 42. Areas of significant concentrations of bromide,
nitrate-N, and chloride in a sprinkler-irrigated
plot (Plot 10-2) 81 days after application of
bromide, 1972. (See Figure 40 for symbol key)
9 - Original location of fertilizer band.
102
-------
O.Or-
D.
LU
Q
0.3
0.6
0.9
1.2
1.5
1.8
2.1
0 12.7 25.4 38.1 50.8 63.5 76.2 88.9 101.6
LATERAL DISTANCE, cm
Figure 43. Areas of significant concentrations of bromide, nitrate-N,
and chloride in a furrow-irrigated plot (Plot 21-1) 81 days
after application of bromide, 1972. (See Figure 40 for
symbol key) @ - Original location of fertilizer band.
103
-------
12.7 25.4
88.9 101.6
Figure 44.
38.1 50.8 63.5 76.2
LATERAL DISTANCE, cm
Areas of significant concentrations of bromide, nitrate-N,
and chloride in a furrow-irrigated plot (Plot 21-2) 81 days
after application of bromide, 1972. (See Figure 40 for
symbol key) 0- Original location of fertilizer band.
104
-------
1.8
J_
0 12.7 25.4 38.1 50.8 63.5 76.2 88.9 101.6
LATERAL DISTANCE, cm
Figure 45. Areas of significant concentrations of bromide, nitrate-N,
and chloride in a subirrigated plot (Plot 36-1) 81 days
after application of bromide, 1972. (See Figure 40 for
symbol key) 0- Original location of fertilizer band.
O - Subirrigation pipe.
105
-------
0.0
0.3 -
1.5
1.8
2.1
12.7 25.4 38.1 50.8 63.5 76.2 88.9 101.6
LATERAL DISTANCE, cm
Figure 46. Areas of significant concentrations of bromide, nitrate-N,
and chloride in a subirrigated plot (Plot 36-2) 81 days
after application of bromide, 1972. (See Figure 40 for
symbol key) 0 - Original location of fertilizer band.
O - Subirrigation pipe.
106
-------
Porous bulbs sample a larger area and would provide better sampling
under situations where the fertilizer is broadcast rather than banded. The
data from porous bulbs are better related to what the quality might be
expected in the water from irrigation return flows than the data from core
samples. However, it is often difficult to obtain consistent porous bulb
data.
LUBBOCK LOCATION
Although the subirrigation system (described in Section 4) was
installed in March, the automation was not completed until July. Sweet
corn which was planted May 16 was at the tassel stage of growth when the
automation was completed. Four switching tensiometers 0.30 m in length in
each of two plots were located 0.15 m to the side of orifices and were set
at potentials of -30 cb and -60 cb. The amount of water applied to the two
plots during the period the system was automated is shown in Table 18.
During the six-day period from July 7 to July 12, 16.8 and 3.9 cm of water
were applied to the -30 cb and -60 cb plots, respectively. Between July 12
and July 22, the system was inoperable due to the necessity of making
changes in automation and flow control valves.
To obtain information concerning soil-water distribution, tensiometers
were installed in late July at 0.10, 0.25, and 0.50 m from an orifice at
two locations in each plot at different depths. Following installation,
2.8 cm of water were applied to each plot. From Figures 47 and 48, it can
be seen that the primary zone of soil-water potential change following irri-
gation occurred below 0.15 m and above 0.90 m. In the -30 cb plot, the
largest increase in potential occurred at 30 cm followed by 0.6 m. Changes
in soil-water potential at 0.15, 0.9, and 1.2 m were negligible, indicating
that there was still retention capacity in the soil profile for storage of
rainfall following the irrigation. Corn in the -60 cb plot yielded
21,000 ears/ha and the -30 cb plot yielded 41,990 ears/ha. Corn in the
-60 cb plot showed visual signs of stress while the -30 cb plot did not.
This soil is underlain with a layer higher in clay content at 0.9 m, which
may be a factor in maintaining a high potential under field conditions.
Changes in soil-water content on the same dates the changes in poten-
tial were measured are shown in Figure 49. It can be seen that major
increases in soil-water content that occurred between August 3 and August 4
were not reflected in increases in soil-water potential at depths greater
than 0.9 m in the -60 cb plot. The access tube for the neutron probe was
0.15 m from the subirrigation line in close proximity to but at a different
location from the tensiometers located 0.1, 0-25, and 0.5 m from the irri-
gation line. It may have been possible that the soil-water content was
different in the area of the access tube and the area where the tensiometers
were located so that no relationship could be expected to exist.
Much better correlation was obtained in the -30 cb plot between the
soil-water content (Figure 49) and soil-water potential (Figure 47).
Changes in both parameters occurred throughout the profile. At the end
of the six-day period, increases in soil-water content occurred in all
107
-------
TABLE 18. CENTIMETERS OF IRRIGATION WATER APPLIED AUTOMATICALLY TO
SUBIRRIGATION PLOTS AT LUBBOCK, TEXAS, DURING 1971
Date
Time
Total
hours
Water
applied,
cm
Total ,
cm
-30 cb plots Two 19-lpm Dole valves
July 7-8
July 8-9
July 9-10
July 10
July 11
July 11-12
7:30 p.m.
8:30 p.m.
9:30 a.m.
4:00 p.m.
12:30 a.m.
3:30 p.m.
- 7:30 a.m.
- 9:30 a.m.
- 1 :30 a.m.
- 6:30 p.m.
- 9:30 a.m.
- 11:00 a.m.
12
13
16
2-1/2
9
19-1/2
2.84
2.99
3.78
0.48
2.13
4.62
16.84
-30 cbplots Two 9.5-1pm Dole valves
July 22 1:00 p.m. - 11:45 a.m. 22-3/4 2.69
July 25-26 9:00 p.m. - 7:30 a.m. 10-1/2 1.24
July 29
July 30
July 30
July 30-31
July 31
July 31
July 31
Aug. 3-4
7:45 p.m.
9:00 a.m.
8:30 p.m.
11:45 p.m.
9:45 a.m.
1:00 p.m.
8:30 p.m.
11 :00 a.m.
- 8:15 p.m.
- 9:30 a.m.
- 9:00 p.m.
- 12:45 a.m.
- 10:15 a.m.
- 4:00 p.m.
- 12:00 p.m.
- 11:00 a.m.
1/2
1/2
1/2
1
1/2
3
3-1/2
24
0.05
0.05
0.05
0.10
0.05
0.36
0.41
2.84
7.84
24.68
-60 cb plots Two 19-lpm Dole valves
July 10 5:30 a.m. - 7:30 a.m. 2 0.46
July 11-12 8:30 p.m. - 11:00 a.m. 14-1/2 3.43
3.89
-60 cb plots Two 9.5-1pm Dole valves
Aug. 3-4 11:00 a.m. - 11:00 a.m. 24 2.84
2.84
6.73
108
-------
0.0
Figure 47.
50 0 50
AUGUST 3 AUGUST 4 AUGUST 9
LATERAL DISTANCE, cm
Soil-water potential (cb) on selected dates in the -30 cb plot before and after
irrigating with 2.8 cm of water between August 3 and August 9 in 1971 at Lubbock,
Texas. 9 - subirrigation pipe.
-------
0.0
0.3
0.6
0.9
1.2 -
AUGUST 3
-50
-40
.-20-
-40
-50'
-60
AUGUST 4
0
AUGUST 9
50
Figure 48.
LATERAL DISTANCE, cm
Soil-water potential (cb) on selected dates in the -60 cb plot before and after
irrigating with 2.8 cm of water between August 3 and August 9 in 1971 at Lubbock,
Texas. ) - subirrigation pipe.
-------
0.0
0.3 -
0.6 -
I 0-9
1.2
1.5
-30 cb PLOT
O
CLAY,
%
21
22
23
23
23
25
28
32
30
42
60 cb PLOT
.10 .20
SOIL-WATER CONTENT, cm/cm
O - AUGUST 3
9 - AUGUST 4
D - AUGUST 9
CLAY,
%
22
22
23
23
24
26
28
31
i
30
42
.10 .20
SOIL-WATER CONTENT, cm/cm
Figure 49.
Soil-water content on selected dates before and after irrigation (2.8 cm of
water applied between August 3 and August 9) in 1971 at Lubbock, Texas.
-------
depths in the -60 cb plot while changes did not occur at 0.45, 0.75, 0.9,
and 1.2 m in the -30 cb plot.
Since decreases in yield occurred with water stress in the -60 cb plot
in 1971, the potential levels of the switching tensiometers were changed
from -30 and -60 to -20 and -40 in 1972. Rainfall was above average
(Table 19) and was evenly distributed throughout the growing season in
1972. Consequently, only 6.35 cm of irrigation water were added to the
-20 cb plot, while the -40 cb plot received 7.72 cm (Table 20). The -40 cb
plot yielded 66,720 ears/ha while the -20 cb plot yielded 59,300 ears/ha.
The cumulative amount of water applied during the growing season compared
to the potential ET as estimated by Jensen, et al. (10) is shown in
Figure 50. During May, the total water received by each plot approximately
equaled the potential ET.
During June, the slope of the cumulative rainfall curve was less than
that of the potential ET curve showing that rainfall received was less than
the ET potential by approximately 20 cm. The soil-water storage of these
soils was adequate to supply this amount.
The studies from Lubbock during 1971 and 1972 indicate that the auto-
mated subirrigation systems apparently do have some of the advantages
hypothesized in the initial project. It is necessary to maintain a low
soil-water potential in only a portion of the profile to adequately supply
crops with water. This leaves room in the soil profile to store water from
rains. This could significantly increase water-use efficiency by minimizing
the amount of water lost to irrigation return flows by making better use of
rainfall and thus applying less irrigation water containing salts.
112
-------
TABLE 19. RAINFALL RECEIVED AT LUBBOCK, TEXAS, BETWEEN THE
EMERGENCE AND HARVEST OF THE 1972 CROP
Date
April 29
Total
May 4
5
6
7
10
11
14
25
26
28
29
30
Total
June 11
13
14
15
17
22
29
30
Total
July 1
3
4
5
6
9
18
19
20
21
Total
Amount,
cm
0.23
0.23
T
0.03
3.48
1.24
1.93
0.76
0.23
T
0.23
0.53
0.03
T
8.46
2.01
5.18
0.94
0.89
0.66
0.05
0.71
0.15
10.59
1.32
3.35
2.01
0.03
T
2.11
0.58
T
0.05
3.84
13.29
113
-------
TABLE 20. IRRIGATION WATER APPLIED AUTOMATICALLY TO
SUBIRRIGATION PLOTS AT LUBBOCK, TEXAS,
DURING 1972
Date
April 20
28
May 1
June 21
23
24
25
26
27
28
July 1
3
17
Total
Water applied, cm
-20 cb Plot
1.09
1.14
1.14
0.36
0.25
0.66
0.33
0.79
0.38
0.33
6.47
-40 cb Plot
1.09
1.14
1.14
1.30
0.76
2.24
0.69
8.36
114
-------
63.5
50.8
38.1
£
o
~ Q
Q.
D-
«=C
o:
LU
25.4
12.7
YIELD:
-20 cb PLOT
-40 cb PLOT
59,300 EARS/HA
66,720 EARS/HA
• CUMULATIVE ETp
A CUMULATIVE RAINFALL
-20 cb PLOT CUMULATIVE
IRRIGATION
D -40 cb PLOT CUMULATIVE
IRRIGATION
DATE
Figure 50. Cumulative amounts of applied water and potential evapotranspiration [Jensen, et al. (10)]
from the automated subirrigated plots at Lubbock, Texas, during 1972.
-------
SECTION 6
RESULTS AND DISCUSSION
OBJECTIVE 1 - CONTRIBUTION OF CURRENT IRRIGATION AND FERTILIZATION PRACTICES
TO POLLUTION OF UNDERGROUND WATER
One of the objectives of this project was to determine the influence of
various irrigation systems on solute movement within and below the soil
profile. In this particular soil, this was a zone between the surface and
the water table, approximately 9.1-m thick. Both porous bulb soil-water
extracts and soil extracts were obtained. Procedures for the analyses of
porous bulb soil-water and soil extracts obtained from the profile are
discussed in Section 4 in chronological order. The order of discussion of
the results is as follows: anions except for nitrate (nitrite, orthophos-
phate, chloride, sulfate), cations (sodium, calcium, magnesium, potassium,
ammonium), conductivity and followed by the most important ion in the study,
nitrate.
Nitrite
Analyses for nitrite from samples obtained during the first year of the
study showed that 0.1 ppm or less existed in the soil; therefore, analyses
were not continued.
Phosphate (Orthpphosphate)
Phosphate values obtained during the course of the study are typical of
those found in Figure 51. Concentrations of the extracts were generally
less than 1 ppm ranging primarily from 0 to 0.3 ppm. Such concentrations of
phosphate are no problem relative to the water quality of irrigation return
flows. Phosphate analyses were, therefore, discontinued after the first
year of the study.
Chloride
Chloride analyses from selected soil-water extracts are shown in
Figures 52 through 56. Average chloride concentration of the irrigation
water was 73.5 ppm as indicated by the vertical line within the graph.
Chloride changes within the first year of the study on a sprinkler irriga-
tion system are shown in Figure 52. Similar changes were found within the
year in the furrow, subirrigation, and automatic subirrigation systems.
Major changes in chloride concentration occurred between 0 and 1.5 m. On
July 8, the concentration of chloride in this zone was low with the peak
116
-------
Q_
LU
Q
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
0 1 2
PHOSPHATE, ppm
Figure 51. Phosphate concentration of porous bulb soil-water extracts from
various depths during 1971 from a sprinkler irrigation system.
117
-------
0.0
O-
UJ
Q
1.5
3.0
4.6
6.1
7.6
9.1
0
AVERAGE IRRIGATION WATER
CONCENTRATION 73.5 ppm
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
50
250
300
100 150 200
CHLORIDE, ppm
Figure 52. Chloride concentration of porous bulb soil-water extracts from
various depths during 1971 from a sprinkler irrigation system.
118
-------
concentration of 130 ppm occurring at 0.3 m. By August 17 the chloride
concentration increased in this zone to 250 ppm at 0.9 m. Data obtained on
September 3 showed a peak chloride concentration at 1.5 m. These data indi-
cate that there was probably a concentration of chloride in the surface from
evaporation. The chloride was leached due to 7.00 cm of rainfall received
between July 8 and August 17 and 17.85 cm of rainfall received between
August 17 and September 3. There appears to be some accumulation of
chloride between 2.1 and 3.0 m between July 8 and September 3. However,
the concentrations are generally less than those in the irrigation water
(40.0 ppm vs 73.5 ppm). The only major change that occurred below 3.0 m
was at 9.1 m where the chloride concentration decreased from 120 ppm to
60 ppm.
Changes in chloride concentrations in soil-water extracts over a two-
year period (1971-1973) for the sprinkler irrigation system are given in
Figure 53. There was a general increase in chloride concentration between
1971 and 1972 between 1.2 and 3.0 m to concentrations greater than those of
the irrigation water. Between the 1971 and 1972 growing seasons, 32.9 cm of
rainfall were received in 25 different rainfall periods. This rainfall was
apparently adequate to move chloride down in the profile but not out of the
profile. In 1973, the chloride concentration was much lower than in the
second year of the study. This was due to rainfall received between the
1972 and 1973 growing seasons. The 70.74 cm received in 40 rainfall periods
was adequate to decrease the chloride content below that of the irrigation
water throughout the profile.
The same trend was followed in the furrow irrigation system between the
surface and 3.0 m in that the chloride content of the extracts decreased
between 1971 and 1972-73 (Figure 54) to a depth of 3.0 m. Data below 3.0 m
were sketchy due to the previously mentioned problems of obtaining soil-
water extracts. There was a consistent increase at 7.6 m. However, these
samples were from within the water table and it is difficult to ascertain
the separate contributions from the water table and leaching through the
soil profile.
In the subirrigation system (Figure 55), there was a general increase
in the chloride concentration immediately at the surface with a major
decrease at 0.6 m where the subirrigation pipe was located. This decrease
was apparent down to 1.5 m. From 1.5 to 3.0 m, there was an increase in the
chloride content during 1972—but a decrease in 1973. The same trend was
true from 6.1 and 7.6 m; i.e., there was an increase in the chloride concen-
tration in the extracts during 1972 but a decrease during 1973. The
decreases between 1972 and 1973 were due to the large amount of rainfall
(70.74 cm) received between the two growing seasons.
In the automatic subirrigation system (Figure 56), the same trend is
also true as with the manual subirrigation system. There was an increase in
the surface, a general decrease down to about 2.0 m, a slight increase from
3.0 to 4.5 m and then a general decrease from 6.1 to 9.1 m between the years
1972 and 1973.
119
-------
i—
Q.
AVERAGE IRRIGATION
WATER CONCENTRATION
73.5 ppm
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
50 75
CHLORIDE, ppm
Figure 53. Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system.
120
-------
0.0
Q.
UJ
Q
1.5
3.0
= 4.6
6.1
7.6
9-1.
Figure 54.
25
50
75
AVERAGE IRRIGATION WATER
CONCENTRATION 73.5 ppm
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
100
125
150
CHLORIDE, ppm
Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system.
121
-------
O.O1
Cu
UJ
Q
1.5
3.0
4.6
6.1
7.6
9.1
Figure 55.
AVERAGE IRRIGATION WATER
CONCENTRATION 73.5 ppm
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
25
100
125
150
50 75
CHLORIDE, ppm
Chloride concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
122
-------
0.0
1.5
3.0
4.6
i—
a.
6.1
7.6
9.1
Figure 56.
AVERAGE IRRIGATION WATER
CONCENTRATION 73.5 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
•25
100
125
150
50 75
CHLORIDE, ppm
Chloride concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
123
-------
In summary, there was a major decrease in the chloride content of soil-
water extracts between 1971 and 1973. Rainfall received (70.74 cm) between
1972 and 1973 was apparently a major factor in improving the quality of the
extracts. The ranking relative to chloride concentration was furrow irriga-
tion > sprinkler irrigation > subirrigation > automated subirrigation. The
lower chloride content of the automated subirrigation system may have been
due to the fact that less chloride was added since less irrigation water was
applied. No major accumulations of chloride were noted under any of the
systems. Chloride concentrations were generally less than the irrigation
water at the end of the three years. It was, therefore, concluded that,
under the conditions of this study, chloride would not be a major pollutant
of the water table.
Sulfate
Sulfate was low in samples taken on July 8, 1971 (Figure 57). It
exceeded the irrigation water concentration (129 ppm) only at the surface
down to 0.6 m and at 2.7 m. Between July 8 and August 17, the sulfate
concentration increased to 600 ppm at 0.6 m with slight increases occurring
at 0.9, 1.2, 1.5, and 1.8 m. Between August 17 and September 3, the peak
at 0.6 m decreased to 300 ppm with other decreases occurring from 0.6 m down
to 1.8 m. These decreases were probably due to 7.77 cm of rainfall received
between August 17 and September 3. It is notable that the same conditions
displaced the chloride peak from 0.6 to 1.5 m (Figure 52) but only decreased
rather than displaced the sulfate peak (Figure 57).
The changes that occurred in sulfate concentrations from 1971 to 1973
in the sprinkler irrigation system are shown in Figure 58. The concentra-
tions in the soil exceeded those of the irrigation water in 1971 in the
surface 0.6, 3.0, and 9.1 m. During 1972 and 1973, the concentrations in
the surface 0.6 m fluctuated but were lower than the irrigation water and
values obtained in 1971. There was an increase in sulfate concentration
between 1.5 and 2.7 m compared to the values obtained during 1971. Between
3.0 and 9.1 m the sulfate concentrations were generally lower in 1972 and
1973 than they were in 1971. The exception to this was at 7.6 m where the
sulfate concentration was higher in 1973 than in 1971 and 1972. At the end
of the three-year period, the soil-water extracts exceeded the concentra-
tions of the irrigation water concentration only at 2.4, 2.7, and 9.1 m. In
general, the quality of irrigation return flows was better in 1973 than 1971
in the sprinkler-irrigated plots.
Sulfate concentrations of soil-water extracts from the furrow irriga-
tion system are shown in Figure 59. The data show a definite movement of
sulfate peaks within the surface 3.0 m between years. The peak at 0.3 to
0.6 m present in 1971 moved to 1.2 m in 1972 and to 2.7 m in 1973. Another
peak was initiated in 1972 and 1973 at 0.3 m, probably from evaporation of
irrigation water. The location of the peak at 2.7 m in the furrow-irrigated
plot was in the same location as one in the sprinkler-irrigated plot
(Figure 58). There was little change in the sulfate concentrations below
3,0 m in the furrow irrigation system.
124
-------
0.0
1.5
3.0
E
ex
UJ
Q
4.6
6.1
7.6
9.1
Figure 57.
AVERAGE IRRIGATION WATER
"CONCENTRATION 129 ppm
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
100
200
300
400
500
600
SULFATE, ppm
Sulfate concentration of porous bulb soil-water extracts from
various depths during 1971 from a sprinkler irrigation system.
125
-------
0.0
1.5
3.0
LU
Q
4.6
6.1
7.6
9.1
0
AVERAGE IRRIGATION WATER
CONCENTRATION 129 ppm
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
50
100
150
200
250
300
Figure 58.
SULFATE, ppm
Sulfate concentration of porous bulb soil -water extracts from
various depths during 1971, 1972 and 1973 from a sprinkler
irrigation system.
126
-------
0.0
1.5
3.0
4.6
UJ
Q
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 129 ppm
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
0
50
200
250
300
100 150
SULFATE, ppm
Figure 59. Sulfate concentration of porous bulb soil-water extracts from
various depths during 1971, 1972 and 1973 from a furrow irri-
gation system.
127
-------
Soil-water extract sulfate concentrations for a subirrigation system
are given in Figure 60. As with chloride, there was a constant decrease in
the sulfate concentration between 1971 and 1973 at 0.6 to 0-9 m due to the
location of the subirrigation pipe. In 1972, there was an accumulation of
sulfate at 1.5m which moved to 2.7 to 3.3 m in 1973. This is the same zone
of increase in the sprinkler (Figure 58) and furrow (Figure 59) irrigation
systems. Below 3.0 m there was an increase in sulfate at 6.0 m, with little
change occurring at 4.6, 7.6, and 9.1 m between 1971 and 1973. At the end
of the three-year period, the sulfate concentration exceeded that of the
irrigation water only at 0.15, 0.3, 2.7, and 3.0 m, indicating that the
quality of the irrigation return flows relative to sulfate was high.
The automated subirrigation system (Figure 61) had by far the lowest
sulfate concentrations in the profile. There was an increase at the surface
as was the case with chloride. There were decreases in sulfate concentra-
tion at 0.3 to 0.6 m, slight increases from 1.5 to 3.0 m, with little change
in concentration occurring below 3.0 m.
In summary, the data indicate that water flow from subirrigation
systems decreased the sulfate concentration at 0.6 to 0.9 m. An accumula-
tion of sulfate was indicated in all three manually-operated systems at
2.7 to 3.0 m (Figures 58 through 60). Peaks of sulfate concentration
remained static while the chloride peaks tended to move in the profile. In
1973, the overall ranking of the sulfate concentration of the soil-water
extracts from the various irrigation systems was furrow irrigation > sprin-
kler irrigation = subirrigation > automatic subirrigation. Below 4.6 m the
sulfate concentrations of the extracts were lower than that of the irriga-
tion water indicating the quality of the leachate reaching the water table
was high from all systems. It was therefore concluded from this study that
sulfate was not a pollution hazard.
Sodium
Changes in sodium concentration obtained during the three years of the
study are shown in Figures 62 through 66. During the growing season most of
the changes in the sprinkler irrigation system (Figure 62) occurred above
1.5m and below 4.6 m. Between 0 and 0.6 m there was a general tendency for
the peak concentration to move down in the soil profile as the season
progressed. An accumulation of sodium was indicated at 1.5 m. Below 4.6 m
there was a decrease in the sodium concentration. There was no significant
relationship between the sodium concentration and the sulfate (Figure 57)
and chloride concentration (Figure 52) between the various dates during the
growing season.
There was a general increase in sodium concentration between 1971 and
1973 between 0 and 3.0 m in the sprinkler irrigation system (Figure 63)
except at 1.2 and 1.5 m. Below 3.0 m there was a decrease in the sodium
concentration of the soil-water extracts between 1971 and 1973. Only at
0.15 and 0.6 m did the concentration exceed the concentration of the irri-
gation water at the end of the three years.
128
-------
AVERAGE IRRIGATION WATER
CONCENTRATION 129 ppm
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
50
100
1!
200
250
300
Figure 60.
SULFATE, ppm
Sulfate concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
129
-------
0.0
371
1.5
3.0
4.6
Q.
LU
Q
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 129 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
50 100 150
SULFATE, ppm
200
250
300
Figure 61
Sulfate concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
130
-------
0.0
Q_
UJ
Q
AVERAGE IRRIGATION WATER
CONCENTRATION 92.2 ppm
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
100 150
SODIUM, ppm
Figure 62. Sodium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irri-
gation system.
131
-------
O.Oi
.5
3.0
4-6
D_
LU
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 92.2 ppm
1 - JULY 8, 1971
1972
1973
50
100 150
SODIUM, ppm
200
250
Figure 63.
Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system.
132
-------
The concentration of sodium in the furrow irrigation system (Figure 64)
was generally higher than the concentration of the sprinkler irrigation
system (Figure 63) at the end of the three-year period. There was a devel-
opment of a sodium peak at 0.3 m under the furrow irrigation system
(Figure 64) between 1971 and 1973 due to evaporation. A peak located at
0.9 m in 1971 moved to 1.2 m in 1972 and 1.5 to 1.8 m in 1973. No signifi-
cant change occurred in the sodium concentration below 3.0 m during the
three years of the study.
Decreases and increases in the manual subirrigation system (Figure 65)
were noted in sodium concentration during the three-year period. Decreases
were noted between 0.3 and 0.6 m where the subirrigation pipe was located.
These ions were apparently moved to the surface and to a zone between 0.9
and 3.0 m. The decrease noted at 0.3 and 0.6 m is similar to that noted
with chloride (Figure 55) and sulfate (Figure 60). Below 3.0 m there was a
decrease in the sodium concentration of the soil-water extracts during the
three-year period.
A zone of low sodium concentration was also noted in the automated
subirrigation system (Figure 66) at 0.3 to 0.6 m where the subirrigation
pipe was located. It is difficult to comment on the samples between 1.5 and
3.0 m since the samples were obtained from different depths on the two dates.
Sampling was a problem in this zone with the automated subirrigation system
due to small amounts of irrigation water added which did not percolate into
this zone. Below 3.0 m there was no change in sodium concentration.
In summary, there were no deleterious accumulations of sodium in the
soil profile during the three years of the study. At the end of the three-
year period, the sodium concentration of extracts below 3.0 m from sprinkler,
subirrigation, and automated subirrigation systems was less than that of the
irrigation water. Only at 7.5 and 9.0 m was the concentration of sodium
from the furrow irrigation system higher than the irrigation water, and
these concentrations did not change during the three years for which soil-
water extracts were obtained. Above 3.0 m the sodium concentration from the
different systems was greatest in the manual subirrigation system followed
by the furrow, sprinkler, and automatic subirrigation systems. The subirri-
gation systems had low concentrations of sodium at 0.3 to 0.6 m where the
subirrigation pipe was located.
Calcium
Calcium data obtained are shown in Figures 67 through 71. During 1971
an overall increase in the calcium concentration of the extracts was indi-
cated at 0.6 m and from 1.8 to 9.1 m in the sprinkler irrigation system
(Figure 67). The movement of a peak was indicated from 1.8 to 2.4 to 2.7 m
between July 8, August 17, and September 35 respectively. However, the
overall increases noted during 1971 below 3.0 m were not noted over the
three years of the study (Figure 68). There was a major increase between
1971 and 1972 at 0.9 m. This peak remained stable and became broader
between 1972 and 1973.
133
-------
0.0
CL
UJ
Q
1.5
3.0
4.6
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 92.2 ppm
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
50
100 150
SODIUM, ppm
200
250
Figure 64.
Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system.
134
-------
0.0
1.5
3.0
4.6
D.
UJ
Q
6.1
7.6
9.1
Figure 65.
AVERAGE IRRIGATION WATER
CONCENTRATION 92.2 ppm
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
50
100
150
200
250
SODIUM, ppm
Sodium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
135
-------
0.0
1.5
3.0
4.6
Q_
LU
6.1
7.6
9.1
Figure 66.
AVERAGE IRRIGATION WATER
CONCENTRATION 92.2 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
50
100
150
200
250
SODIUM, ppm
Sodium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
136
-------
0.0
D-
LU
Q
1.5
3.0
4.6
6.1
7.6
9.1
Figure 67.
AVERAGE IRRIGATION
WATER CONCENTRATION
63 ppm
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
50
150
200
100
CALCIUM, ppm
Calcium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irriga-
tion system.
137
-------
O.Ol
1.5
3.0
re
I—
O_
4.6
6.1
7.6
9.1
Figure 68.
AVERAGE IRRIGATION WATER
CONCENTRATION 63 ppm
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
50
200
250
100 150
CALCIUM, ppm
Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system.
138
-------
The primary changes in the furrow irrigation system (Figure 69) occurred
between 1971 and the last two years of the study. Increases in the calcium
concentration of the extracts from 1971 to 1972 between 0.6 and 1.2 m and
1.8 to 9.1 m remained stable through 1973. The rains received between 1972
and 1973 apparently did not affect the calcium concentrations as they did
the chloride concentrations (Figure 54).
Decreases in the calcium concentration in the 0.15-to 0.9-m zone in the
manual subirrigation system (Figure 70) were similar to those of other ions
(Figures 55, 60, and 65). A major increase in calcium concentration to
170 ppm at 2.1 m was noted in 1972. However, in 1973 the calcium concentra-
tion of the extracts was approximately equal to that of the irrigation water
(63 ppm).
The automated subirrigation system (Figure 71) had a low calcium concen-
tration in the zone of influence of the subirrigation pipe (0.3 to 0.6 m).
Increases in calcium concentration were noted at 0.15 and 0.9 m indicating
the subirrigation system had moved the calcium to the periphery of its appli-
cation zone. Calcium concentrations of extracts below 1.5 m were lower in
1973 than in 1972.
In summary, the overall quality of the irrigation return flow with
respect to calcium at the end of the three-year period was high. The order
of calcium concentrations at the end of the three-year period with respect
to irrigation systems was furrow > sprinkler > subirrigation > automatic
subirrigation. The sprinkler irrigation system had the highest concentra-
tions above 1.5m while the furrow irrigation system had the highest concen-
tration below 1.5 m. At the end of the three-year period, the calcium
concentration of the extracts was approximately equal to that of irrigation
water in the manually-subirrigated plots and less than irrigation water in
the automatically-subirrigated plots. Since less water was applied through
the automated subirrigation systems, it appears that the amount of water
applied as well as the irrigation system may influence the ion concentration
in the profiles below irrigations systems.
Magnesium
Data on magnesium concentration of soil-water extracts from the various
irrigation systems are shown in Figures 72 through 75. These data were
obtained only during the 1972 and 1973 crop years. In the sprinkler irriga-
tion system (Figure 72), there was some increase in concentration in the
surface at the 0.3 and 0.9 m depths as well as the 2.7 and 6.1 m depths.
Otherwise, there was a general decrease in the magnesium concentration
between the two years. Concentrations of the extracts exceeded those of
the irrigation water (43.3 ppm) only below 2.7 m, and these values decreased
during the two years.
Concentrations of magnesium in the surface 1.5m were lower in the
furrow irrigation system (Figure 73) than the sprinkler irrigation system
(Figure 72). Increases in magnesium occurred between the surface and 1.2 m
at 1.5, 1.8, and 2.1 m and 4.6 m down to 9.1 m in the furrow irrigation
system. There was a general overall increase between 1972 and 19/J, but
139
-------
0.0
Q_
LU
Q
1.5
3.0
4.6
6.1
7.6
9.1
Figure 69.
AVERAGE IRRIGATION WATER
CONCENTRATION 63 ppm
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
50
150
200
100
CALCIUM, ppm
Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system.
140
-------
0.0
1.5
3.0
4.6
Qu
LU
Q
6.1
7.6
9.1
Figure 70.
AVERAGE IRRIGATION WATER
CONCENTRATION 63 ppm
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
50 100
CALCIUM, ppm
150
200
Calcium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
141
-------
0.0
h-
UJ
Q
1.5
3.0
4.6
6.1
7.6
9-1,
Figure 71.
AVERAGE IRRIGATION WATER
CONCENTRATION 63 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
50 100
CALCIUM, ppm
150
200
Calcium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
142
-------
0.0
D_
LU
Q
1.5
3.0
4.6
6.1
7.6
9.1
Figure 72.
AVERAGE IRRIGATION WATER
CONCENTRATION 42.3 ppm
1 - MAY 4, 1972
2 - JUNE 20, 1973
10
20
40
50
60
30
MAGNESIUM, ppm
Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a sprinkler
irrigation system.
143
-------
0.0
AVERAGE IRRIGATION WATER
CONCENTRATION 42.3 ppm
1 - JUNE 5, 1972
2 - JUNE 24, 1973
20 30
MAGNESIUM, ppm
Figure 73. Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a furrow irriga-
tion system.
144
-------
the final concentrations in the profile were not as great as they were in
the sprinkler irrigation system.
In the subirrigation system (Figure 74), the magnesium concentrations
were similar to those obtained for other ions (Figures 55, 60, 65, and 70)
in that there was a decrease at 0.6 m in the major zone of influence of the
subirrigation pipe. With the exception of this depth, the magnesium concen-
trations increased between the surface and 2.4 m in both the manual sub-
irrigation and automated subirrigation systems (Figure 75). Below 2.4 m,
the magnesium concentration decreased under both systems. In 1973, the
magnesium concentration of the extracts exceeded the concentrations of the
irrigation water only at 2.1 m.
In summary, the sprinkler-irrigated plots had the highest magnesium
concentrations followed by the furrow-irrigated plots with the subirrigated
plots being the lowest. In general, the magnesium concentrations of the
soil extracts from the root zone (0 to 1.5 m) tended to be lower than the
concentrations of the irrigation water while the calcium concentrations
tended to be higher than those of the irrigation water. This suggests that
a portion of the magnesium applied in the irrigation water was adsorbed by
the clays or precipitated to a less soluble form. None of the magnesium
concentrations of the soil-water extracts from any of the systems were high
enough to be of concern.
Potassium
Potassium concentrations obtained during the course of the study are
shown in Figures 76 through 80. Changes that occurred during 1971 in the
sprinkler irrigation system are shown in Figure 76. In general, potassium
remained high in the surface meter throughout the growing season. This
indicates that it was being made available at a constant rate from the soil.
Data in Figure 77 indicate somewhat of a decrease in the surface 0.9 m
between 1971 and 1973 in the sprinkler-irrigation system. There is some
indication of a tendency toward slight accumulations in the lower part of
the profile during 1972 between 1.5 and 1.8 m. However, these concentra-
tions were not noted in 1973. The concentrations were higher at 0.6 m in
1973 than they were in 1971 indicating the possibility of leaching. How-
ever, below 1.8 m the concentrations were slightly less or approximately
equal to those of the irrigation water following the first year of the
study. No massive amounts of leaching were occurring compared to the
amounts produced in the surface, indicating that the excess potassium may
have reacted with the clay.
Data from the furrow irrigation system indicate little change
(Figure 78). This plot was land leveled; consequently, part of the mica-
ceous minerals which were high in potassium was probably removed from the
surface and the potassium in solution in the resulting top soil is not as
great as that top soil which was removed. In general, the potassium con-
centrations below 1.5m were approximately equal to that of the irrigation
water, 2.8 ppm.
145
-------
0.0
1.5
3.0
E
^"4.6
i—
Q_
LU
Q
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 42.3 pprn
1 - MAY 5, 1972
2 - JUNE 19, 1973
10
50
60
Figure 74-
20 30 40
MAGNESIUM, ppm
Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from a manual subirri-
gation system.
146
-------
O.Or
Q_
LU
Q
AVERAGE IRRIGATION WATER
CONCENTRATION 42.3 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
20 30 40
MAGNESIUM, ppm
Figure 75. Magnesium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
147
-------
0.0
1.5
3.0
" 4.6
CL.
LLJ
Q
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 2.8 ppm
Figure 76.
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
10
35
40
45
15 20 25 30
POTASSIUM, ppm
Potassium concentration of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irrigation
system.
148
-------
0.0
1.5
3.0
4.6
Q.
6.1
7.6
9.1
AVERAGE IRRIGATION WATER
CONCENTRATION 2.8 ppm
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
10
30
35
40
45
Figure 77.
15 20 25
POTASSIUM, ppm
Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system.
149
-------
0.0
1.5
3.0
4.6
D-
U->
Q
6.1
7.6
9-1 1
0
AVERAGE IRRIGATION WATER
CONCENTRATION 2.8 ppm
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
10
35
40
45
15 20 25 30
POTASSIUM, ppm
Figure 78. Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system.
150
-------
The sub-irrigation system (Figure 79) yielded data very similar to the
sprinkler irrigation system (Figure 77) in that there was a decrease in the
potassium concentration at the surface between 1971 and 1973. There was a
slight increase at 1.8 to 2.1 m indicating some movement out of the zone
around the subirrigation line to this particular area. The decreases in the
surface were greater than that of the sprinkler-irrigated plot, indicating
that the surface may have been drier with less moisture available to make
the potassium available.
The same trend holds for the automated subirrigation system (Figure 80)
in that the surface remained higher with a zone of low concentration at
0.6 m. There was some indication that there was an increase in potassium
concentrations at 0.9 to 1.8 m, indicating again some movement out of the
zone where the subirrigation pipe was located.
In summary, the greatest potassium concentrations were sprinkler irri-
gation system followed by the manual subirrigation system, automated subirri-
gation and furrow irrigation system. Soil minerals are indicated to play a
major role in the production of potassium in that the land leveled furrow
irrigation system had very low potassium concentrations in the soil solution.
Ammonium
Typical ammonium-N concentrations found during the course of the study
are shown in Figures 81 through 84. Changes that occurred during 1971 in a
sprinkler plot to which Uran was chisel-applied are shown in Figure 81.
Concentrations were generally low at all sampling points and dates with the
exception of samples obtained on August 17 and September 3 at 6.1 m.
Data for the same plot for sampling dates in 1971, 1972, and 1973 are
shown in Figure 82. Concentrations of ammonium-N were uniformly low except
for 1.2 and 6.1 m on May 4, 1972. By June 20, 1973, concentrations measured
at these depths were similar to those at other depths.
Ammonium-N concentrations found in a furrow-irrigated plot treated with
Uran banded in the bed at a level above the bottom of the water furrow for
three sampling dates are shown in Figure 83. Concentrations were again
generally low with only two samples having concentrations exceeding 3.0 ppm.
These were at 1.5 and 2.1 m on May 8, 1972.
Data from a similarly treated manually-subirrigated plot shown in
Figure 84 indicate a similar trend as found in the two previously discussed
systems. Ammonium-N concentrations were generally low except for isolated
samples (e.g., 0.6 and 2.4 m on July 8, 1971; and 0.9, 1.8, 2.4, 4.6, and
7.6 m on May 5, 1972).
In summary, while there was some evidence of ammonium-N in the profile
below the root zone, the inconsistency with which it was found in concentra-
tions above 3.0 ppm make assessment of movement impossible. Generally,
ammonium-N concentrations were uniformly low and would appear to be of
little consequence from the standpoint of irrigation return flow degradation.
151
-------
0.0
1.5
3.0
F 4.6
0_
UJ
Q
6.1
7.6
Figure 79.
10
AVERAGE IRRIGATION WATER
CONCENTRATION 2.8 ppm
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
35
40
45
15 20 25 30
POTASSIUM, ppm
Potassium concentration of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
152
-------
0.0
3.0
£
i 4.6
t—
D_
LU
Q
6.1
7.6
9.1
Figure 80.
.AVERAGE IRRIGATION WATER
CONCENTRATION 2.8 ppm
1 - MAY 30, 1972
2 - JUNE 4, 1973
10
30
35
40
45
15 20 25
POTASSIUM, ppm
Potassium concentration of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
153
-------
3.0
Q_
UJ
Q
7.6
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
0 5 10 15 20 25 30
AMMONIUM-N CONCENTRATION, ppm
Figure 81. Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler-irrigated
plot fertilized with Uran banded in the bed.
154
-------
0.0
3.0
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
7.6
10
15
20
25
30
Figure 82.
AMMONIUM-N CONCENTRATION, ppm
Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler-irrigated plot fertilized with Uran banded in the
bed.
155
-------
O.Oi
1 - JULY 8, 1971
2 - MAY 8, 1972
3 - JUNE 22, 1973
3.0
Q_
LU
Q
4.6
6.1
7.6
Figure 83.
10
15
20
25
30
AMMONIUM-N CONCENTRATION, ppm
Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a furrow-
irrigated plot fertilized with Uran banded in the bed.
156
-------
0.0
0.
UJ
Q
I - JULY 8, 1971
2 - MAY 8, 1972
3 - JUNE 20, 1973
0 5 To 15 20
AMMONIUM-N CONCENTRATION, ppm
Figure 84. Ammonium-N concentrations of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manually-subirrigated plot fertilized with Uran banded in
the bed.
157
-------
Conductivity
Conductivities of soil-water extracts for the various irrigation
systems during the three years of the study are given in Figures 85 through
89. In general, the conductivity of the soil-water extracts was less than
the conductivity of the irrigation water applied during 1971 for sprinkler
irrigation .(Figure 85). The peak at 0.9 m on September 3 is somewhat related
to the calcium concentration (Figure 67). Between the beginning and end of
the measurement period the conductivity decreased at depths below 3.0 m.
Between 1971 and 1973 there was a slight increase in the conductivity
of the 0 to 1.5-m zone, little change between 1.5 and 3.0 m, and a decrease
below 3.0 m in the sprinkler irrigation system (Figure 86). There was
little discernible change in conductivity of soil-water extracts of the
furrow irrigation system (Figure 87). In the manual subirrigation system
(Figure 88), there was a decrease at 0.15 and 0.9 m and increases at 1.5 and
1.8 m. Other changes were minimal. In the automated subirrigation system
(Figure 89), there was an overall decrease in conductivity so that, through-
out the soil profile, the values in 1973 were all less than for the irriga-
tion water applied.
In summary, the conductivity was highest in the sprinkler irrigation
system with the furrow irrigation and manual subirrigation systems being
intermediate and the automated subirrigation system being the lowest. Since
most values were lower than the average irrigation water conductivity of
947 lamhos, it was concluded that the salt load in the irrigation return flow
was not a potential pollution hazard under .the conditions of this study.
This concludes an overall discussion of the ions measured and conduc-
tivity with the exception of nitrate. Since nitrate was higher in the soil-
water extracts and is a major item of concern in the area, it will be
discussed in more detail than the other ions. Since none of the above ions
are indicated to be degrading the quality of the irrigation return flow in
these particular soils, no further discussion of these ions will be under-
taken. The discussion of nitrate in soil samples and porous bulb soil-water
extracts follows.
Nitrate
Control or Unfertilized Plots--
Average nitrate-N concentration of the irrigation water was 6.7 ppm.
As would be suspected, much higher values for nitrate-N were noted in the
control plots throughout the study due to nitrate-N mineralized from the
soil and plant material. Values for the sprinkler-irrigated plots
(Figure 90) and furrow-irrigated plots (Figures 91 and 92) are typical of
those obtained during the growing season in 1973. In the sprinkler-
irrigated plot (Figure 90), concentrations of 50-ppm nitrate-N were obtained
on June 4 at 2.1 m. A movement of nitrate-N was indicated by concentration
decreases from 0 to 0.9 m, increases at 1.5 m, decreases at 2.1 m, and
increases at 4.6 m as the season progressed. A similar movement was noted
in one of the furrow-irrigated control plots (Figure 91) as the nitrate-N
158
-------
0.0
1.5
3.0
4.6
D-
UJ
a
6.1
7.6
9.1
Figure 85.
AVERAGE IRRIGATION WATER
CONDUCTIVITY 947 y mhos
1 - JULY 8, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
1_
500
1000 1500
CONDUCTIVITY, 11 mhos
2000
2500
Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971 from a sprinkler irrgation
system.
159
-------
O.Oi
D-
LLJ
Q
1.5
3.0
4.6
6.1
7.4
9.1
Figure 86.
AVERAGE IRRIGATION WATER
CONDUCTIVITY 947 y mhos
1 - JULY 8, 1971
2 - MAY 4, 1972
3 - JUNE 20, 1973
500
2000
2500
1000 1500
CONDUCTIVITY, y mhos
Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
sprinkler irrigation system.
160
-------
0.0.
1.5
3.0
4.6
D_
UJ
Q
6.1
7.6
9.11
Figure 87.
AVERAGE IRRIGATION WATER
CONDUCTIVITY 947 y mhos
1 - JULY 8, 1971
2 - JUNE 5, 1972
3 - JUNE 24, 1973
500
2000
2500
1000 1500
CONDUCTIVITY, y mhos
Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
furrow irrigation system.
161
-------
0.0,
1.5
3.0
4.6
D-
LU
Q
6.1
7.6
9.1
Figure 88.
500
JWERAGE IRRIGATION WATER
CONDUCTIVITY 947 y mhos
1 - JUNE 25, 1971
2 - MAY 5, 1972
3 - JUNE 19, 1973
1000
1500
2000
2500
CONDUCTIVITY, ]i mhos
Electrical conductivity of porous bulb soil-water extracts
from various depths during 1971, 1972 and 1973 from a
manual subirrigation system.
162
-------
0.0,
1.5
3.0
4.6
Q_
UJ
Q
6.1
7.6
9.1)
Figure 89.
AVERAGE IRRIGATION WATER
CONDUCTIVITY 947 y mhos
1 - MAY 30, 1972
2 - JUNE 4, 1973
500
2000
2500
1000 1500
CONDUCTIVITY, u mhos
Electrical conductivity of porous bulb soil-water extracts
from various depths during 1972-1973 from an automatic
subirrigation system.
163
-------
0.0
1.5
3.0
4.6
Q-
UJ
Q
6.1
7.6,,
9.1
50.3
SPRINKLER-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 6, 1973
10
40
50
Figure 90.
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot.
164
-------
0.0
10
FURROW-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
40
50
20 30
NITRATE-N, ppm
Figure 91. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot.
165
-------
FURROW-IRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
40
50
Figure 92.
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot.
166
-------
increased from 10 ppm to 45 ppm at 2.1 m. The increases were not as dramatic
in the other furrow-irrigated plot (Figure 92). However, there was an
increase in nitrate-N from 1.2 to 1.8 m. No major changes in nitrate-N
concentrations were noted below 4.5 m during 1973.
In general, there was an increase in the nitrate-N content of porous
bulb extracts in the sprinkler-irrigated plots (Figure 93) and furrow-
irrigated plots (Figures 94 and 95) below 1.5 m between 1971 and 1973. In
the sprinkler-irrigated plot (Figure 93), the nitrate-N increased from 3 to
30 ppm between the end of the 1971 and 1973 growing seasons. In one of the
furrow-irrigated control plots (Figure 94), the major increase in nitrate-N
of the soil-water extracts occurred between 1.2 and 3.0 m between 1971 and
1973. In the other furrow-irrigated plot (Figure 95), the increases were
between 4.6 and 7.1 m.
As can be seen in Figures 93, 94, and 95, there was considerable vari-
ability among the three plots in clay content at the various depths. It is
notable that the higher nitrate-N values occurred in or just above zones of
higher clay content.
In summary, relatively large increases in nitrate-N concentrations were
found in porous bulb extracts from control plots between 1971 and 1973.
This finding made it difficult to determine the separate contributions of
soil nitrogen and fertilizer nitrogen. Consequently, a study in which the
fertilizer was tagged with 15N was initiated in 1973 to delineate the sepa-
rate contributions and will be reported in another section. The increases
noted between 1971 and 1973 indicate the possibility of a contribution of
nitrate-N from soil nitrogen in unfertilized plots to irrigation return
flow. The movement of this nitrogen was apparently influenced by the
textural characteristics of the soil profile.
All irrigation in the Knox County area is currently by furrow or sprin-
kler irrigation systems. Most of the nitrogen fertilizer is applied in
bands below the water furrow either as ammonia or Uran. Discussion relative
to the current methods of applying various nitrogen sources in furrow irri-
gation systems follows.
Ammonia Banded Below the Level of the Water Furrow--
Where ammonia was applied (Figure 96) in 1973, there was little change
in nitrate-N concentrations below 1.5 m except at 3.0 m. With the exception
of this depth, the data obtained were similar to those obtained from the
adjacent unfertilized plot (Figure 92). As would be expected, there was
more nitrate-N in the surface 1.5 m in the plot fertilized with ammonia
(Figure 96) than in the unfertilized plot (Figure 92). For the three-year
period, the nitrate-N in the soil-water extracts in the unfertilized plots
(Figure 95) and plots fertilized with ammonia (Figure 97) was similar below
3 m. This is further emphasized in a comparison of the nitrate-N content of
porous bulb samples obtained from a control and ammonia-treated plot on
July 2 (Figure 98). The data indicate that little nitrate-N was contributed
to irrigation return flow from ammonia applied below the level of the water
furrow.
167
-------
0.0
Q-
LU
a
7.6
9.1
CLAY,
%
9
16
23
17
13 (1.5 m)
19
25
19
11
14 (3.0 m)
8
6
4
4
10 (4.6 m)
8
10
14
13
17 (6.1 m)
SPRINKLER-IRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 5, 1972
3 - JULY 6, 1973
40
50
Figure 93.
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot.
168
-------
0.0
1.5 ,
FURROW-IRRIGATED
- SEPTEMBER 11, 1971
- JUNE 10, 1972
- JULY 11, 1973
10
20 30
NITRATE-N, ppm
CLAY,
°/
10
7
15
21
17
17 (1.5m)
17
20
20
17
13 (3.0 m)
11
7
7
13
15 (4.6 m)
21
21
19
21
17 (6.1 m)
23
31
25
40
50
Porous bulb soil -water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot.
169
-------
- 4.6
n.
LU
6.1
7.6
9.1
CLAY,
%
8
12
14
18
20 (1.5 m)
24
17
14
17
15 (3.0 m)
13
12
11
18
18 (4.6 m)
20
18
22
20
26 (6.1 m)
FURROW-IRRIGATED
SEPTEMBER 3, 1971
JUNE 30, 1972
JULY 11, 1973
40
-5S
20 30
NITRATE-N, ppm
Figure 95. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot.
170
-------
Figure 96.
FURROW-IRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
20
30
40
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded below the level of the water furrow.
171
-------
Q.
UJ
Q
9.1
Figure 97.
FURROW-IRRIGATED
1 - AUGUST 17, 1971
2 - JUNE 12, 1972
3 - JULY 11, 1973
10
20 30
NITRATE-N, ppm
40
50
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
anhydrous ammonia banded below the level of the water furrow.
172
-------
FURROW-IRRIGATED
TREATMENT
1 - CONTROL
2 - AMMONIA
SAMPLE DATE
JULY 2, 1973
JULY 2, 1973
10
20
30
40
50
Figure 98.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by soil
depth for a control plot and plot with anhydrous ammonia banded
in the bed below the bottom of the water furrow, 1973. (Total
N - 374 kg/ha).
173
-------
Uran Banded Below the Level of the Water Furrow--
The nitrate-N concentration of the soil-water extracts where Uran was
banded below the level of the water furrow under furrow irrigation systems
(Figures 99 and 100) was considerably higher than extracts from the unferti-
lized plot (Figures 92 and 95), especially below the root zone. Figure 99
shows the increase as the season progressed in 1973. At the beginning of
the season on April 1, nitrate-N values down to 3.0 m were low. On June 4,
high values for nitrate-N were noted in the surface 0.6 m due to the addi-
tion of fertilizer. With the exception of 4.6 m, increases in nitrate-N were
noted from 1.5 to 9.1 m on July 11, 1973. All values for nitrate-N in the
plot where Uran was banded below the level of the water furrow (Figure 99)
were significantly higher than those obtained for the unfertilized plots
(Figure 92).
Increases in the nitrate-N in the soil-water extracts were also noted
to have occurred at depths from 2.7 to 7.6 m between 1971 and 1973 in the
plot in which Uran was banded (Figure 100). The values were significantly
higher than those in an adjacent unfertilized plot (Figure 95). A dramatic
difference between the controls and the plot where Uran was banded can be
seen where the two treatments are compared on the same graph (Figure 101).
It thus appears that Uran banded below the level of the water furrow
(Figure 100) has more potential to add nitrate-N to irrigation return flow
than no fertilization (Figure 95) or ammonia applied below the level of the
water furrow (Figure 97).
Uran Applied in the Irrigation Water—
Since Uran is commonly applied in the irrigation water in both furrow
and sprinkler irrigation systems, such a treatment was included in this
study. Figure 102 shows the data obtained during 1973 from furrow-irrigated
plots. It can be seen that the nitrate-N values were higher than those of
the unfertilized plot (Figure 92) and the plots to which ammonia was banded
(Figure 96) but lower than the plot in which Uran was banded (Figure 99).
The same general trend was true between 1971 and 1973 (Figure 103). The
significantly higher concentration of nitrate-N of the plot where Uran was
applied in the irrigation water over the control can be seen in Figure 104.
Values of 60- to 70-ppm nitrate-N in the soil-water extracts were also
obtained during 1973 at 0.6 and 3 m, respectively, where Uran was applied
through the sprinkler irrigation system (Figure 105). These high values
were noted on both June 4 and July 10 and exceeded the values obtained from
the control plots on the same date (Figure 90). There was also a major
increase between 1971 and 1973 in the sprinkler-irrigated plot where Uran
was applied in the irrigation water (Figure 106) which was also higher than
the unfertilized plot (Figure 93). A direct comparison between the control
plot and plot where Uran was applied in the irrigation water (Figure 107)
on June 26 shows that the nitrate-N content of the fertilized plots was
significantly higher below 3 m.
In summary, the data obtained between 1971 and 1973 showed much greater
increases in nitrate-N concentrations in porous bulb soil-water extracts
where Uran was used (Figures 99, 102, and 106) than where ammonia was
applied (Figure 97) or the plots that were not fertilized (Figures 93 and 95).
174
-------
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
30
40
50
Figure 99.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by soil
depth during 1973 for a plot treated with Uran banded below the
level of the water furrow.
175
-------
O.Or,
60
FURROW-IRRIGATED
] - AUGUST 17, 1971
2 - JUNE 28, 1972
3 - JULY 11, 1973
20 30
NITRATE-N, ppm
40
50
Figure 100. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
Uran banded below the level of the water furrow.
176
-------
0.15
Figure 101
FURROW-IRRIGATED
TREATMENT SAMPLE DATE
1 - CONTROL - JULY 2, 1973
2 - URAN - JULY 2, 1973
"20
30
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and plot treated with Uran
banded in the bed below the bottom of the water furrow,
1973. (Total N - 368 kg/ha)
177
-------
O.Of
I - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
NITRATE-N, ppm
Figure 102. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran applied
in the irrigation water.
178
-------
O.Of
CX.
UJ
Q
FURROW-IRRIGATED
1 - SEPTEMBER 3, 1971
2 - JULY 5, 1972
3 - JULY 11, 1973
20
30
40
50
NITRATE-N, ppm
Figure 103. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water.
179
-------
O.Of
FURROW-IRRIGATED
TREATMENT
1 - CONTROL
SAMPLE DATE
- JULY 2, 1973
2 - URAN - IRRIGATION - JUNE 26, 1973
WATER
20
30
40
50
Figure 104.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and a plot treated with Uran
for three years, 1973. (Total N - 375 kg/ha)
180
-------
rr:
I—
a.
LU
Q
SPRINKLER-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 10, 1973
10
20
30
40
50
Figure 105.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran applied
in the irrigation water.
181
-------
7.6
SPRINKLER-IRRIGATED
9.1
Figure 106.
I
1
,
3 1 - SEPTEMBER
/2 - JUNE 22,
3 - JULY 10,
3, 1971
1972
1973
10
20
30
40
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water.
182
-------
0.0
1.5
3.0
4.6
6.1
7.6
9.1
0
SPRINKLER-IRRIGATED
TREATMENT
CONTROL
URAN - IRRIGATION
WATER
SAMPLE DATE
JUNE 26, 1973
JUNE 26, 1973
10
20
30
40
50
NITRATE-N, ppm
Figure 107. Porous bulb soil-water extract nitrate-N concentrations by soil
depth for a control plot and a plot treated with Uran for three
years, 1973. (Total N - 364 kg/ha)
183
-------
Highest increases in nitrate-N below the root zone (>1.5 m) between 1971 and
1973 occurred in the furrow-irrigated plot where the Uran was banded below
the level of the water furrow (Figure 100) and in the sprinkler-irrigated
plot when it was applied in the irrigation water. A comparison of the clay
content with the peak nitrate-N of the soil-water extracts indicates that
peak nitrate-N concentrations occurred in or above the zones of highest clay
content. The high nitrate-N concentration of the unfertilized plots
(Figures 90 through 95) shows the problems of delineating the separate
contributions of soil nitrogen and fertilizer nitrogen to irrigation return
flow and necessitated the addition of a study in which the fertilizer was
tagged with 15N to determine the separate contributions of the two compo-
nents.
These foregoing data show conclusively that some fertilizer nitrogen
apparently was moving toward the water table below the root zone; however,
it should be pointed out that these samples were taken from point sources in
the profile and from the standpoint of total movement of nitrate to the
water table would represent more of a qualitative than a quantitative
measurement.
This can more clearly be seen in Figures 108 and 109. These data were
obtained from soil samples taken at five equidistant locations laterally
across the bed and down to a depth of 5.5 m. The samples were taken in
30-cm increments and a 1:1 sodium sulfate extract made and nitrate deter-
mined. The data in Figure 108 compares the extracts obtained at the begin-
ning of the study in 1971 with those obtained from soil samples taken in
August of 1974 from sprinkler-irrigated plots to which 508 and 514 kgofN/ha
had been banded in the form of Uran and ammonia, respectively. It can
readily be seen that when based on soil extracts the high nitrate-N concen-
tration peaks did not occur but rather that the nitrate-N while increasing
from 1971 to 1974 was more evenly distributed throughout the profile than
indicated from the porous bulb extracts. The concentration levels, while
increasing to some extent, still remained relatively low. Consequently,
while it is evident that fertilizer nitrogen was contributing to an increase
in nitrate-N in the irrigation return flow for currently-used sprinkler
irrigation and fertilization practices, this contribution based on these
data would appear to be relatively low.
Similarly, the data in Figure 109 for a furrow-irrigated plot, to which
ammonia was banded using current fertilization practices, show an increase
in nitrogen extractable from the soil in the nitrate form above that
obtained from similar soil samples taken in 1971. Again, as for the sprin-
kler irrigation system, while there is an increase in nitrogen concentra-
tion, this increase seems to be rather low when put on a soil basis. The
depth of the increase above the 1971 samples was not quite as great as that
of the sprinkler system, as shown in Figure 108. Therefore, while it is
evident that some increase in nitrate-N occurred in the soil profile, these
increases would appear to be relatively small.
184
-------
0.0!
0.6
1.2
1.8
E 2.41-
•V
rc
3.0
3.6
4.3
4.9
5.5
0
2
3
SPRINKLER-IRRIGATED
TREATMENT
BEFORE
TREATMENT
URAN BANDED
AMMONIA
SAMPLE
DATE
1971
- 1974
- 1974
12
TOTAL N
APPLIED,
kg/ha
0
508
514
1<
16
2 4 6 8 10
NITRATE-N, ppm
Figure 108. Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974.
185
-------
o.Or
0.6
FURROW- IRRIGATED
TREATMENT
BEFORE TREATMENT
AMMONIA BANDED BELOW
LEVEL OF WATER FURROW
SAMPLE
DATE
1971
- 1974
I
TOTAL N
APPLIED,
kg/ha
0
514
12
14
16
Figure 109.
6 8 10
NITRATE-N, ppm
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974.
186
-------
Model for Leaching of Nitrate From Warm Sandy Soils
Due to the variability in the soils located at the site and the problems
encountered with previously discussed analytical and statistical models, it
was decided to develop an empirical model for nitrate movement using data
from the site. A discussion of this development follows:
Basic Assumptions—
Nitrate was assumed to move with the soil water. Water movement was
assumed to be one-dimensional piston displacement. Availability of nitrate
from organic material was limited by the rate of mineralization rather than
nitrification. Denitrification was neglected. Temperature effects on
nitrogen reactions were neglected. Plant uptake of nitrate-N was propor-
tional to the nitrate concentration at a particular depth but was not
influenced by location within the root zone. Water added in excess of
field capacity drained rapidly through the soil profile. Evaporation was
neglected. Other assumptions are implicit within the model functions.
Evaluation—
The model consists of equations describing the various physical
processes. Constants in these equations were chosen by a procedure in
which the sum of squares of differences between predicted and measured
values of soil nitrate-N amounts was minimized. All constants were varied
simultaneously to decrease that sum until an optimum combination was
achieved.
Initial Conditions and Input Data--
Input data were obtained during an 87-day growing season in which sweet
corn was grown in a loamy fine sand. Initial conditions include distribu-
tion of soil nitrate and soil water with depth. Initial conditions which
were estimated by the optimization of model constants were amount and distri-
bution of nitrogen available from the organic matter for mineralization and
nitrification.
Input data with time include rainfall, irrigation, fertilization,
potential ET, LAI, uptake of nitrogen by the crop, and the relationship for
calculating transpiration from leaf area and potential ET. Input data which
were estimated by the optimization of model constants include the relation-
ship between the root-zone depth and crop age. The model could be modified
slightly to consider incorporation of crop residues.
The Algebraic Model - Nitrogen Relations--
The top 150-cm thickness of the soil profile was divided into five
30-cm layers. Calculations of nitrogen reactions (and water movement) were
made daily. The net rate of mineralization was assumed to be slower than
the rate of nitrification. The rate of mineralization-nitrification (RMIN)
in a soil layer was defined by the equation,
RMIN = A7(ARNV) + A8(CN03) [12]
in which A7 and A8 are constants, ARNV is the amount of N available for
mineralization and nitrification from organic residue in the layer, and
187
-------
CMOS is the amount of nitrate-N now present in the layer. Units of RMIN,
ARNV, and CN03 are kg N/ha per 30-cm layer.
The initial amount and distribution of residue N per cm, RNV, was
obtained by optimizing the constants in the equation
RNVD = RNVD=0 e [13]
in which A2 and RNVp=g are constants, and D is soil depth in cm. The units
of RNVn_n and RNV are kg of available N per ha-cm.
u~~u
The daily increase in nitrogen in the above ground portion of the crop
(PLANT) had been measured. The total plant uptake of nitrate-N, PUP,
kg N03-N/ha per day was obtained by
PUP = A12(PLANT) [14]
in which A12 is an optimized constant.
The layers in the soil from which this nitrate-N was taken were deter-
mined from an equation relating root-zone depth in 30-cm layers (RZD) and
plant age (DAY):
fll A
RZD = (A13)(DAY) [15]
in which A13 and A14 are constants which were optimized in the model evalu-
ation. The value of RZD was rounded to the next highest integer. Nitrate
extracted from a particular layer was assumed proportional to the amount of
nitrate-N in that layer, that is nitrate-N in that layer was reduced by the
equation
CN03 = CN03 - PUP(CN03/SUCON) [16]
in which SUCON is the sum of the nitrate-N amounts in the root zone, RZD,
and the other variables are as defined.
Nitrate-N amounts were as adjusted to account for mineralization-
nitrification, RMIN from Equation 12,
CN03 = CN03 + RMIN [17]
Sodium nitrate fertilizer nitrogen was added to the top 30-cm layer.
The Algebraic Model - Water Relations--
For calculation of water movement, the soil was also divided into five
30-cm layers. The layers in the root zone, RZD, supplied water for tran-
spiration. If the leaf area index was £3., transpiration was equal to
potential evapotranspiration. For values of leaf area index S3., transpira-
tion was calculated from the equation,
188
-------
0-6137
TRANS = ETP [18]
in which TRANS is the transpiration in mm, ETP potential evapotranspiration
in mm, calculated by the method of Jensen, et al. (10), and VLAI is the leaf
area index.
Drainage from a layer in the soil profile was permitted when the water
content exceeded the field capacity of the layer, A4. The units of A4 are
mm of water per 30-cm layer. However, drainage was limited so that the
vertical movement of N did not exceed 30 cm per day. Daily amounts of rain
plus irrigation were added to the top 30-cm layer of soil.
Optimum Constants and Goodness of Fit--
Optimum values of the model constants are
initial RNVD_Q = 11.
A2 = -0.075
A4 = 62.
A7 = 0.065
A8 = -0.012
A12 = 1.2
A13 = 1.6
A14 = 0.06
Soil nitrate values were measured at two locations and four dates on
Plot 6 during 1973. The top 150-cm layer of soil was divided into five
30-cm layers for measurement. The minimum sum of squares of differences
between these 40 measured values and the corresponding 40 calculated values
was 18,273 [kg/ha-30 cm]2. The two locations were intended as replications.
The sum of squares of differences between 20 comparable measured nitrogen
amounts in each location was 10,540 [kg/ha-30 cm]2. A graphical comparison
of predicted and measured values is given in Figure 110. The model under-
estimated peak values on the first two sampling dates and overestimated
peak values on the last two sampling dates.
Predicted Leachate Concentrations With Various Input Conditions--
Once the model constants were determined, the model was used to predict
leachate concentrations occurring with the various combinations of input
conditions shown in Table 21. Other data, rainfall, transpiration, poten-
tial plant uptake of N, etc., were the same as those used to seek model
constants.
For the 528 combinations, amounts of water and nitrate-N leached past
the 150-cm depth were calculated. Whenever leaching reduced nitrate amounts
in the root zone below that needed to adequately supply the crop, the
deficiency was noted. The sum of daily deficiencies was used to calculate
a ratio of N supplied to plants to N needed by plants. The amount of
nitrate-N remaining in the top 150-cm of soil at the end of the 90-day
season was also computed. Average concentrations of mtrate-N in the
leachate are shown in Figures 111 and 112 as a function of the ratio of
189
-------
VO
o
140
120
100
60
o
40
20
0
1 - MEASURED
2 - COMPUTED
DAY 87
0 30 60 90 120 150 30 60 90 120 150 30 60 90 120 150 30 60 90 120 150
DEPTH, cm
Figure 110. Comparison of predicted values of soil nitrate with measured values at a depth of
30 cm. Values plotted are the average of two locations.
-------
TABLE 21. VARIOUS INPUT CONDITIONS MODELED
Aval
residue
Surface cm,
kg/ha-cm
0
10
20
30
Table
nitrogen
Total profile,
kg/ha
0
133
267
400
Fertilizer
nitrogen,*
kg/ha
0
100
200
300
Net ETt
between
irrigations,
mm
20
40
60
Irrigation amounts
divided by net ET
since
last irrigation
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
*0ne-fourth of the fertilizer was added at planting; three-fourths was
sidedressed 30 days later. Fertilizer was assumed to be in the form
of nitrate.
tTranspiration minus rainfall.
irrigation amounts to net ET. Minimum levels of nitrogen additions which
were ample for plants are noted in Table 22. Leachate concentrations were
low when excess water was not applied. The model was written in Fortran for
the IBM 370 computer. Compile time averaged about 10 seconds. Computation
time was slightly less than 0.38 seconds per 87-day season.
Conclusions--
The model presented is an approximate empirical model intended for use
in determining relative effects. The two most important factors affecting
leachate concentrations of nitrate-N during a single growing season are
irrigation amounts and total nitrogen amounts. The source of nitrogen,
fertilizer or residue, had little effect on concentration of mtrate-N in
the leachate. When irrigation amounts were equal to the net ET, the amounts
of N and water leached past the 150-cm depth were almost negligible
(Table 22).
For the conditions modeled, maximum concentrations of nitrate-N in the
leachate occurred when the ratio of irrigation amounts to net ET was about
2.4 (Figures 111 and 112) with large amounts of nitrate-N present. This
condition could readily occur when furrow irrigation systems are used to
irrigate shallow-rooted crops grown in sandy soils. In some areas with
sand? soils, such as East Texas, the annual precipitation is about 2 5 times
the net annual lake evaporation. In such areas it wouId be mos* J^tant
to limit the amount of nitrate-N in the root zone by sma 1 frequent applica-
tions of N or possibly by addition of slow-release fertilizers.
The hydraulic conductivity of the soil modeled is very small at soil-
water potentials Sigh enough to support most crops. Therefore, tensiometers
191
-------
90
80
1. 70
Q.
1 -
2 -
3 -
4 -
SUPPLIED
NEEDED N
100
75 to 99
50 to 74
<50
N
1C
o
fee
cc
o
o
o
CD
LU
>
eC
60
50
40
30
20
10
x 100
RESIDUE N,
kg/ha
FERTILIZER N,
I kg/ha
\l
(400, 100)
(267, 200)
(133, 300)
(400, 0)
(267, TOO)
3 (133, 200)
(0, 300)
(267, 0)
(133, 100)
(0, 200)
(133, 0)
(0, 100)
(0, 0)
1.0 1.5 2.0 2.5 3.0 3.5
IRRIGATION AMOUNT DIVIDED BY NET ET
4.0
Figure 111. Relationship between leachate concentrations, excess water
additions, and fertility levels. Irrigations were applied
when the net evapotranspiration was 20 mm.
192
-------
SUPPLIED N
90
0
1.0
Figure 112.
RESIDUE N,
kg/ha
FERTILIZER N,
I kg/ha
(400, 100)
(267, 200)
(133, 300)
(400, 0)
(267, 100)
(133, 200)
(0, 300)
(267, 0)
(133, 100)
(0, 200)
(133, 0)
(0, 100)
(0, 0)
1.5 2.0 2.5 3.'0 3.5 4.0
IRRIGATION AMOUNT DIVIDED BY NET ET
Relationship between leachate concentrations, excess water
additions, and fertility levels. Irrigations were applied
when the net evapotranspiration was 60 mm.
193
-------
TABLE 22. MINIMUM LEVELS OF FERTILITY FOR AMPLE PLANT NITROGEN (PLANTS USED 164.35 KG OF NITROGEN
PER HA)
Net ET at
irrigation,
mm
20
60
20
60
20
60
20
60
20
60
20
60
Residue
nitrogen,
fertilizer
nitrogen,
kg/ha
(0, 200)
(0, 200)
(0, 200)
(0, 200)
(133, TOO)
(133, 100)
(133, 100)
(133, 100)
(267, 0)
(267, 0)
(0, 300)
(0, 300)
Ratio of
irrigation
to net ET
1.0
1.0
1.2
1.2
1.0
1.0
1.2
1.2
1.0
1.0
1.0
1.0
Concentration
of nitrogen
in leachate,
ppm
4.27
4.27
4.97
4.56
4.30
4.30
5.40
4.80
4.33
4.33
4.27
4.27
Nitrate-N
left in
profile,
kg/ha
43.0
43.0
41.6
41.8
70.8
70.8
69.3
69.5
98.6
98.6
127.6
127.6
Drainage,
mm
12.6
12.6
41.6
41.6
12.6
12.6
41.6
41.6
12.6
12.6
12.6
12.6
Nitrate-N
leached,
kg/ha
0.54
0.54
2.10
1.90
0.54
0.54
2.20
2.00
0.55
0.55
0.54
0.54
-------
in the lower root zone could indicate sufficiently low potentials and
conductivities to virtually eliminate drainage. Automated sprinkler or drip
systems with switching tensiometers located in the upper root zone could
probably be used to automatically limit irrigation amounts.
For the conditions modeled, the model indicated a relatively rapid
mineralization of available organic-N of about 6.5% per day. The word
"available" is used to suggest that some organic-N would not be mineralized.
Therefore, if green crop residue is incorporated into a warm, wet soil in
late summer, it is possible that much of the nitrogen would be mineralized
and available for leaching by winter rains.
Fertilization can increase nitrate-N concentrations in leachate to
levels in excess of 10 ppm. This can occur even with moderate fertilizer
applications (133 to 200 kg/ha) and reasonably good irrigation management.
Organic matter decomposition can cause leachate concentrations ^10 ppm
nitrate-N. However, it is probable that high leachate concentrations of
nitrate-N can be avoided even with fertilization for good yields. To
achieve this desirable result, a decision-making process as suggested in
Figure 113 may need to be adopted.
Bromide Movement as Affected by Excess Water
As previously discussed, bromide was determined to be an excellent
indicator of nitrate movement. During 1973 and 1974, bromide was added
using different methods of application to selected plots in the various
irrigation systems (Sprinkler Plots 6, 7, 8, 9, 12, and 13; Furrow Plots
18, 19, 20, 23, 24, and 25; Subirrigation Plots 32, 33, 34, 35, 38, 39, 40,
and 41). Different amounts of irrigation water were added and records of
the rainfall were obtained. Although some of the plots were irrigated with
an amount equal to potential ET as previously discussed, measurements of
soil-water content were made to obtain better estimates of the actual ET of
the crop. Rainfall received between the 1973 and 1974 growing seasons was
adjusted by eliminating showers less than 6 mm and subtracting 6 mm from
rains greater than 6 mm. Bromide was determined on soil samples as previ-
ously described periodically during the two-year period.
The data obtained are shown in Figure 114. The high r value of .879
indicates a good relationship between the two parameters. The scatter of
tfie data (Figure 114) is not surprising in view of the variability in
texture below the surface (Figure 10, p. 40) and the different types of
water movement from the different irrigation systems. The piston movement
of the bands described in the previous section was exhibited to a large
extent all the way to the water table located at 5.5 m. The scatter of the
points at 5.5 m would suggest that less water is needed to move the bromide
to this depth than indicated by the regression line. However, since this
is the depth of the water table, less actual water may have been required
to move the bromide to this depth, and little movement occurred once the
bromide reached this depth as diffusion is a relatively slow process.
The scatter of the points between 1.8 and 4.3 m could probably be
explained by including a correction factor for soil texture from each of
195
-------
START OF CROP
IS
MOISTURE
ADEQUATE
FOR GERMI-
NATION
IRRIGATE
TO WET
SEED ZONE
AN SOI
NITROGEN
ESTABLISH
ROP
ADD SMALL
AMOUNT
NEAR SEED
IS
MOISTURE
ADEQUATE
IRRIGATE TO
ONLY RESUPPLY
WATER USED
ADD IN
INCREMENTS
TO UPPER
ROOT ZONE
S MOR
NITROGEN
NEEDED
IS
CROP
MATURE
AN CRO
EXTRACT
ITROGEN
IS SOIL
NITROGEN
HIGH
MIGHT RAIN LEACH
NITROGEN BEFORE
NEXT CROP
PLANT
COVER
CROP
INCORPORATE
RESIDUE
LET CROP
EXTRACT
NITROGEN
DELAY RESIDUE
INCORPORATION
[TILL JUST PRIOR
TO NEXT CROP
IS OR WILL SO
BE WARM ENOUGH
OR NITRIFICATIO
Figure 113.
YES
Decision flow chart for limiting leaching of nitrate-N from
sandy soils.
196
-------
0.6 _
12.7 25.4 38.1 50.8 63.5
WATER ADDED IN EXCESS OF EVAPOTRANSPIRATION
AND EVAPORATION, cm
76.2
Figure 114.
Relationship between depth of bromide and_water added in
excess of evapotranspiration and evaporation.
197
-------
the different plots. However, from a practical standpoint, this does not
seem necessary. These samples were obtained from a 4-ha block of land
typical of the area. From the standpoint of irrigation return flow, the
interest will be relative to a given large area rather than from a specific
plot with a specific texture because detailed sampling such as occurred at
this location will not be possible over the area of this soil series due to
expense. The regression equation on Figure 114 indicates that for each cm
of water in excess of evaporation and ET the bromide moved 7.4 cm. Between
sweet corn crops, 15.2 to 25.4 cm of rainfall in excess of evaporation were
received during the studies between 1971 and 1974. Thus, excess nitrate in
the profile at the end of the season could be expected to reach the water
table in three to five years if a crop such as sweet corn were grown from
rainfall received between growing seasons. The furrow irrigation systems
commonly used in the area are very inefficient. The experience with furrow
irrigation in this study indicates that two to three times the amount of
water necessary for crop production may be applied or 30.5 to 60.9 cm excess
water. If this is the case, it is possible that excess nitrate may be moved
to the water table in one to two years due to a combination of rainfall and
excess irrigation water.
In summary, the regression equation obtained from bromide data indi-
cates that for each cm of water added in excess of ET and evaporation,
nitrate (which moves similar to bromide) will move down 7.4 cm in the pro-
file. If a crop such as sweet corn is grown, excess nitrate in the profile
can be expected to reach the water table in three to five years from rain-
fall between crops. If excess water is applied during the growing season,
it may reach the water table in one to two years.
OBJECTIVE 2 - POTENTIAL OF USING MODIFIED CURRENT IRRIGATION AND
FERTILIZATION PRACTICES FOR IMMEDIATE REDUCTION OF POTENTIAL POLLUTION
Several modifications to current irrigation and fertilization practices
were investigated as to their potential to enhance the quality of irrigation
return flow. A discussion of these modifications follows.
Furrow Irrigation Systems
Fertilizer Placement--
One simple modification was to apply the fertilizer in the bed rather
than below the level of the water furrow. Figure 115 shows the results
obtained during 1973 in a furrow-irrigated plot to which ammonia was
applied. It can readily be seen that the nitrate-N content of the soil-
water extracts was much higher in the surface 1.2 m than where the fertili-
zer was banded below the level of the water furrow (Figure 96) or in the
control plot (Figure 92). Values of 64 and 594 ppm nitrate-N were obtained
at depths of 0.3 and 0.6 m, respectively, compared to values of 20 and
15 ppm or less where the fertilizer was banded below the level of the water
furrow and where no fertilizer, respectively, were the treatments. There
was an increase in the nitrate-N concentration of the soil-water extracts
between 1971 and 1973 at 4.6 and 6.1 m (Figure 116). However, the final
concentrations at these depths were only 4 to 8 ppm greater than plots where
no fertilizer was applied (Figure 95) or the fertilizer was applied below
198
-------
9.1
0
FURROW-IRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
10
40
50
20 30
NITRATE-N, ppm
Figure 115. Porous bulb soil-water extract m'trate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded in the bed.
199
-------
O.Of
O-
UJ
Q
FURROW-IRRIGATED
1 - AUGUST 17, 1971
2 - JUNE 28, 1972
3 - JULY 11, 1973
9.11
10
20
30
40
50
Figure 116.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with anhydrous ammonia banded in the bed.
200
-------
the water furrow (Figure 97). These differences could be considered minor
and would probably not offset the value of the increased nitrate-N in the
root zone.
Differences between methods of applying anhydrous ammonia can more
easily be seen in a direct comparison of the nitrate-N concentrations in
1973 of the porous bulb soil-water extracts when anhydrous ammonia was
applied in the bed both above and below the bottom of the water furrow
(Figure 117) in the furrow-irrigated system. The previously discussed
nitrate-N concentrations were higher at all depths where anhydrous ammonia
was applied above rather than below the water furrow. The desirable large
higher concentrations in the root zone (<1.0 m) will probably offset the
smaller higher concentrations below the root zone (>1.5 m).
The analyses of soil extracts (Figure 118) from samples obtained in
1974 also give credence to the idea that anhydrous ammonia banded in the
bed may be superior to anhydrous ammonia banded below the level of the water
furrow. These data show that the nitrate-N was higher in the root zone (0
to 1.5 m) where the ammonia was applied in the bed and higher below the root
zone (2 to 3.8 m) where anhydrous ammonia was banded below the level of the
water furrow.
Neither the concentration of nitrate-N of the porous bulb extracts
obtained in 1973 nor the extracts from soil samples obtained in 1974 from
both methods of placement at depths below the root zone were high enough to
be of concern. However, there was a trend for the placement in the bed to
be superior over placement below the water furrow.
Uran was also banded in the bed in the furrow-irrigated plots. The
nitrate-N content of the soil-water extracts in 1973 was not as high where
the Uran was banded (Figure 119) as where ammonia was banded (Figure 115) in
the bed. This might be due to the fact that some of the Uran nitrogen was
already in the nitrate form and more readily absorbed by the crop while it
was necessary for the ammonia to be converted to nitrate. The highest
values for the ammonia plots were obtained at the end of the growing season
when there were no plants to utilize the nitrogen.
With the exception of a high value for nitrate-N at 0.5 m in the plot
where the Uran was banded below the water furrow (Figure 99) and at 0.9 m
where the nitrogen was banded in the bed (Figure 119), there was little
difference in the two treatments in the root zone. Below 1.5 m, however,
the nitrate-N concentration of the soil-water extracts was significantly
higher where the Uran was banded below the water furrow (Figure 99) than
where it was banded in the bed (Figure 119). The same was true between 1971
and 1973. The nitrate-N concentration in the root zones (0 to 1.5 m) was
higher where the fertilizer was banded in the bed (Figure 120). Between
1.5 and 7.6 m, however, the nitrate-N of the soil-water extracts was much
higher at the end of the three-year period where the Uran was banded below
the water furrow (Figure 100) than above the water furrow.
A direct comparison between plots where Uran was banded in the bed and
below the level of the water furrow (Figure 121) in 1973 also emphasizes the
201
-------
0.0
1.5
FURROW-IRRIGATED
TREATMENT
AMMONIA BANDED IN BED
AMMONIA BANDED BELOW
LEVEL OF WATER FURROW
SAMPLE DATE
- JULY 2, 1973
- JULY 2, 1973
Figure 117.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by soil
depth for plots treated with anhydrous ammonia banded at differ-
ent depths for three years, 1973. (Total N - 374 kg/ha)
202
-------
0.0
0.6
1.2
1.8
2.4
0.
UJ
Q
3.0
3.6
4.3
4.9
5.5
FURROW-IRRIGATED
TREATMENT
BEFORE TREATMENT
AMMONIA BANDED IN BED
AMMONIA BANDED BELOW
LEVEL OF WATER FURROW
SAMPLE
DATE
- 1971
- 1974
- 1974
TOTAL N
APPLIED,
kg/ha
0
514
514
12
14
16
Figure 118.
2 4 6 8 10
NITRATE-N, ppm
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974.
203
-------
Q_
LU
Q
Figure 119.
FURROW-IRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran banded
in the bed.
204
-------
9.1,
FURROW-IRRIGATED
1 - AUGUST 17, 1971
2 - JUNE 28, 1972
3 - JULY 11, 1973
10
20
30
40
50
NITRATE-N, ppm
Figure 120. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran banded in the bed.
205
-------
0.0
1.5
3.0
CL.
UJ
Q
4.6
6.1
7.6
9.1
Figure 121.
FURROW-IRRIGATED
TREATMENT
URAN BANDED IN BED
URAN BANDED BELOW LEVEL
OF WATER FURROW
SAMPLE DATE
- JULY 11, 1973
- JULY 2, 1973
10
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth for plots treated with Uran banded at different
depths for three years, 1973. (Total N - 368 kg/ha)
206
-------
higher concentration of nitrate-N in this zone. The nitrate-N concentration
of porous bulb samples where Uran was banded below the level of the water
furrow was significantly higher compared to Uran banded in the bed or any of
the ammonia treatments (Figure 117).
When extracts from soil samples are compared from plots where Uran was
applied above and below the water furrow (Figure 122), it can be seen that
there was a major increase in nitrate-N in the surface 1.8 m between 1971
and 1974. The increase was greater where the Uran was applied below the
level of the water furrow than above the level of the water furrow. This nitro-
gen would still be available for plant growth if leaching did not occur and
is much higher than samples obtained from anhydrous ammonia-treated plots
(Figure 118). Below 1.8 m, samples from the anhydrous ammonia-treated plots
contained more nitrate-N than samples from the Uran-treated plots
(Figure 122).
Sulfur-Coated Urea--
Sulfur-coated urea was banded in the bed for all irrigation systems.
In the furrow irrigation system, the values for nitrate-N in the soil-water
extracts were generally low both within the root zone (0 to 1.5 m) and below
the root zone (>1.5 m) during 1973 (Figure 123) and 1971-1973 (Figure 124).
The exception to this was the data obtained on July 11, 1973 between 1.5 and
3.0 m. These data indicate that some nitrate was made available from the
sulfur-coated urea that was not utilized by the crop. With the exception of
this date, the nitrate-N of the soil-water extracts was similar to that
obtained from the unfertilized plots both during 1973 (Figure 123 vs
Figure 92) and 1971-1973 (Figure 124 vs Figure 95). The values were much
less than any of the previously discussed treatments.
Ammonia + N-Serve—
During 1971, both ammonia (Figure 125) and ammonia + N-Serve
(Figure 126) were treatments in the study. In both treatments the nitrate-N
was high in the root zone (0 to 1.5 m). Below 1.5 m there was little
difference between the two treatments. Since the N-Serve did not delay the
conversion of ammonia to nitrate and there was no increase in yield through
using N-Serve, treatments with N-Serve were discontinued at the end of the
1971 growing season.
Sprinkler Irrigation System
Fertilizer Placement—
Treatments, with the exception of different vertical placements, dis-
cussed above for the furrow irrigation systems were also evaluated on the
sprinkler irrigation system. Where ammonia was applied in the bed in 1973
(Figure 127), nitrate-N concentration of the soil-water extracts was high
in the root zone. The concentrations were higher than in the unfertilized
plot (Figure 90) and similar to the values obtained where ammonia was
applied in the bed in the furrow-irrigated plot (Figure 115). Nitrate-N
was high in the root zone (0 to 1.5 m) at the end of the growing season
1971 through 1973 (Figure 128). Below 2.1 m there was a concentration
increase in the soil-water extracts between 1971 and 1973. The increases
relative to depth and amount were greater than the values obtained in the
207
-------
o.o r
0.6
1.2
1.8
2.4
Q_
LU
Q
3.0
3.6
4.3
4.9
5.5'
FURROW-IRRIGATED
TREATMENT
BEFORE TREATMENT
URAN BANDED IN BED
URAN BANDED BELOW LEVEL
OF WATER FURROW
SAMPLE
DATE
1971
1974
1974
TOTAL N
APPLIED,
kg/ha
0
508
508
12
14
16
Figure 122.
2 4 6 8 10
NITRATE-N, ppm
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974.
208
-------
0.0
9.1
FURROW-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
20
30
40
50
Figure 123.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-
coated urea banded in the bed.
209
-------
0.0
9.1
0
10
FURROW-IRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 1, 1972
3 - JULY 11, 1973
40
50
20 30
NITRATE-N; ppm
Figure 124. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
sulfur-coated urea banded in the bed.
210
-------
Cu
UJ
Q
*0,15 m - 1
0.30 m - 2
0.45 m - 2
0.60 m - 2
1.20 m - 3
FURROW-IRRIGATED
1 - JUNE 25, 1971
2 - JULY 8, 1971
3 - AUGUST 17, 1971
20 30
NITRATE-N, ppm
Figure 125. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with anhydrous
ammonia banded in the bed.
211
-------
0.0
1.5
3.0
^
\
f^
1 * 0.15 m - 1 -
2 -
1 3-
y n
f / 0.30 m - 2 -
/ / 0.45 m - 2 -
/ / 3 -
92
104.5
70.6
104.5
57
70.6
Q-
LU
Q
4.6
6.1
FURROW-IRRIGATED
7.6
1 - JUNE 25, 1971
2 - JULY 8, 1971
3 - AUGUST 17, 1971
4 - SEPTEMBER 3, 1971
9.1,
10
20
30
40
50
Figure 126.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with anhydrous
ammonia + N-Serve banded in the bed.
212
-------
Figure 127.
SPRINKLER-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 6, 1973
10
20
30
40
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with anhydrous
ammonia banded in the bed.
213
-------
9.1
Figure 128.
SPRINKLER-IRRIGATED
1 - AUGUST 17, 1971
2 - JULY 5, 1972
3 - JULY 6, 1973
10
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
anhydrous ammonia banded in the bed.
214
-------
unfertilized plot (Figure 93). The increases can more easily be seen when a
control plot is compared directly with a plot where anhydrous ammonia was
applied in the bed over the three-year period (Figure 129). The nitrate-N
concentration of the porous bulb extracts was significantly higher where
anhydrous ammonia was applied over the three-year period.
Nitrate-N concentration of soil-water extracts where Uran was applied
in the bed (Figure 130) were, in general, lower than in the unfertilized
plot (Figure 90). The concentrations were thus much less than those in the
plot fertilized with ammonia on the same date (Figure 127). With the excep-
tion of the concentration of 52 ppm at 1.2 m, the nitrate-N concentrations
where Uran was banded in the bed (Figure 131) were less than in the unferti-
lized plot (Figure 93) between 1971 and 1973.
Soil data obtained in 1974 where Uran was banded in the bed in the
sprinkler irrigation system (Figure 108) also showed little change between
1971 and 1974. The nitrate-N concentration in soil extracts of samples from
the sprinkler-irrigated plot was much less than where Uran was applied
either in the bed or below the level of the water furrow in the furrow irri-
gation system (Figure 122). Also included in Figure 108 are nitrate-N data
from a plot where anhydrous ammonia was applied for four years in the bed in
a sprinkler-irrigated plot. The nitrate-N concentrations where anhydrous
ammonia was applied were higher than those obtained where Uran was applied
in the sprinkler irrigation system and were approximately equal to those
obtained where anhydrous ammonia was banded in the bed in the furrow irri-
gation system (Figure 118). The data thus indicate that fertilizer applied
in the bed is one of the better treatments to minimize nitrate-N concentra-
tions in the soil solution below the root zone under sprinkler irrigation.
Sulfur-Coated Urea--
The soil-water extracts from plots fertilized with sulfur-coated urea
under sprinkler irrigation (Figure 132) in 1973 were much higher in
nitrate-N than the extracts from the sulfur-coated, urea-fertilized, furrow-
irrigated plot (Figure 123) and the unfertilized plot (Figure 90) at 3.0 to
6.1 m and lower at 0.6 to 3.0 m. Changes between 1971 and 1973 in the
sulfur-coated urea sprinkler-irrigated plot (Figure 133) compared to the
furrow-irrigated plot (Figure 123) and the unfertilized plot (Figure 93)
followed the same trend. Nitrate-N in extracts from soil samples obtained
in 1974 showed an increase in furrow-irrigated plots from 3.0 to 5.5 m
(Figure 134) and an increase in sprinkler-irrigated plots from 0.6 to 3.0 m
(Figure 134), thus indicating the same trend.
Irrigation Criteria
Criteria for applying irrigation water were (a) visual (when signifi-
cant leaf curl occurred), (b) when tensiometers reached -20 cb potential at
30 cm and (c) when tensiometers reached -40 cb potential at 30 cm. In 1971,
approximately 7.62 cm of water were applied, and in 1972-3, water equal to
the potential ET in a given time period was applied when the above-mentioned
criteria were met. As previously discussed, problems were encountered in
production of the corn crop in 1971 and 1972. In 1971, the seed quality was
poor, and in 1972, poor initial plant development occurred due to a nitrogen
215
-------
O.Oi
1.5
3.0
E
1C
4.6
6.1
7.6
9.1
0
Figure 129.
SPRINKLER-IRRIGATED
TREATMENT
CONTROL
AMMONIA IN
THE BED
SAMPLE DATE
- JUNE 26, 1973
- JUNE 28, 1973
10
20
30
40
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth for a control plot and a plot treated with anhy-
drous ammonia for three years, 1973. (Total N - 374 kg/ha)
216
-------
D_
UJ
Q
0
SPRINKLER-IRRIGATED
1 - APRIL 11, 1973
2 - JULY 4, 1973
3 - JULY 11 , 1973
20
30
40
50
Figure 130.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by soil
depth during 1973 for a plot treated with Uran banded in the
bed.
217
-------
:r
h-
Q.
UJ
Q
Figure 131.
SPRINKLER-IRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 4, 1972
3 - JULY 11, 1973
20 30
NITRATE-N, ppm
40
50
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
Uran banded in the bed.
218
-------
0.0
1.5
3.0
4.6
UJ
Q
6.1
7.6
9.1
10
SPRINKLER-IRRIGATED
1 - APRIL 11, 1973
2 - JUNE 4, 1973
3 - JULY 10, 1973
20 30
NITRATE-N, ppm
40
50
Figure 132.
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-coated
urea banded in the bed.
219
-------
0.0
D_
UJ
Q
. 4,6
9.
Figure 133.
SPRINKLER-IRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 5, 1972
3 - JULY 10, 19.73
20 30
NITRATE-N, ppm
40
50
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
sulfur-coated urea banded in the bed.
220
-------
:r
h-
Q_
LjJ
Q
0.0
0.6
1.2
1.8
2.4
3.0
3.6
4.3
4.9
5.5
TREATMENT
BEFORE TREATMENT
SPRINKLER-IRRIGATED
FURROW-IRRIGATED
SAMPLE
DATE
- 1971
- 1974
- 1974
0
8
10
12
14
16
NITRATE-N, ppm
Figure 134. Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of sulfur-coated
urea application and irrigated by different systems, 1974.
(Total N - 518 kg/ha)
221
-------
deficiency in the surface which was corrected in 1973 by sidedressing at
planting. These problems are expressed in the erratic yields obtained in
1971 and 1972 (Table 23). In 1973, when good quality seed were planted and
the crop was sidedressed with a small amount of nitrogen, the yields were
much higher and more consistent.
TABLE 23. YIELD AND IRRIGATION APPLICATION DATA OF TREATMENTS SPRINKLER-
IRRIGATED BY DIFFERENT CRITERIA
Criteria for irrigation
Visual
Water
applied,
cm
1971
1972
1973
Total
Avg.
Total
Avg.
(1971-3)
(1971-3)
(1972-3)
(1972-3)
25.
27.
26.
79.
26.
56.
27.
40
94
42
76
57
36
18
Yield,
ears/ha
24
26
47
99
33
74
37
,710
,872
,876
,458
,153
,748
,374
-20 cb potential
Water
appl ied,
cm
38.10
25.40
25.53
89.03
29.68
50.93
25.46
Yield,
ears/ha
27
14
53
95
31
67
33
,799
,517
,126
,442
,814
,643
,821
-40
cb potential
Water
applied,
cm
22.
27.
20.
71.
23.
48.
24.
86
94
32
12
71
26
13
Yield,
ears/ha
13,590
18,224
47,875
79,689
26,563
66,099
33,049
There were some differences in the amount of water required where the
different criteria were used. In 1971, more water was applied to the -20 cb
than the visual and -40 cb treatments. In 1972 the reverse was true in that
more water was applied to the visual and -40 cb treatments than the -20 cb
treatments. The irrigation water applied to the visual and -20 cb treat-
ments was approximately equal, and higher than the -40 cb plot in 1973. Rain-
fall amounts during the growing season for 1971, 1972 and 1973 were 23.34,
23.83 and 10.57 cm, respectively. It is interesting to note that .the
difference in irrigation water requirement between the -20 cb and -40 cb
treatments in 1972 and 1973 (0.13 to 7.62 cm) was less than the difference
in the growing season rainfall between the two years (13.16 cm).
With the exception of the 38.10 cm of irrigation water applied to the
-20 cb plot when 7.62 cm was applied at each application, the maximum
difference in water applied between all treatments was only 7.62 cm (20.32
to 27.94 cm). There were no major differences in yields due to irrigation
criteria in 1973 when major production problems did not occur. It thus
appears that there is no significant difference among the various criteria
used relative to yield and the amount of irrigation water required if the
producer has the capability to apply water equal to the ET.
Few differences in nitrate movement were observed in plots irrigated by
the various criteria (Figures 135, 136, and 137). Initially (July 8, 1971),
222
-------
0.0
1C
I—
O-
SPRINKLER-IRRIGATED
- JULY 85 1971
- SEPTEMBER 3, 1971
-- JUNE 5, 1972
- JULY 11, 1973
20
30
40
50
Figure 135.
NITRATE-N, ppm
Porous bulb soil-water extract m'trate-N concentrations by
soil depth during 1971. 1972 and 1973 for a plot treated with
Uran oanded in the bed ana irrigated when significant leaf
curl occurred.
223
-------
0.0
D-
UJ
Q
6.1
7.6 •
9-1
Figure 136.
SPRINKLER-IRRIGATED
JULY 8, 1971
SEPTEMBER 3, 1971
JUNE 5, 1972
JULY 11, 1973
10
20 30
NITRATE-N, ppm
40
50
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
Uran banded in the bed and irrigated when the tensiometer
reached -20 cb potential.
224
-------
I—
Q_
UJ
Q
SPRINKLER-IRRIGATED
JULY 8, 1971
SEPTEMBER 3, 1971
JUNE 5, 1972
JULY 11, 1973
0
40
50
Figure 137.
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
Uran banded in the bed and irrigated when the tensiometer
reached -40 cb potential.
225
-------
the profile of the visual and -20 cb plots was higher in nitrate-N in the
root zone (0 to 1.5 cm) than the -40 cb plot. From 1.5 to 6.1 m, the -40 cb
plot had higher nitrate-N levels in the soil-water extracts than the other
two treatments. At the end of the study, the -20 and -40 cb plots had higher
concentrations of nitrate-N than the leaf curl criteria. Below 6.1 m there
was little difference among treatments.
Summary
Nitrate-N from soil-water extracts where ammonia and Uran were applied
in the bed was much higher in the root zone (0 to 1.5 m) than where ammonia
was applied below the water furrow indicating the fertilizer was better
located to be utilized. Nitrate-N was less in the plots where Uran was
banded in the bed than in the unfertilized plots in the sprinkler irrigation
system. Banding fertilizer in the bed appears to be superior to banding
fertilizer below the water furrow from the standpoint of maintaining high
nitrate-N levels in the root zone.
In the plots fertilized with sulfur-coated urea, nitrate-N values were
low in the furrow-irrigated plot but high in the sprinkler-irrigated plot
for some unexplained reason. No advantage was obtained from treating with
ammonia + N-Serve over ammonia alone.
Thus, it appears that if conditions are adequate to produce a good corn
crop, it makes little difference if the criteria used for applying water is
leaf curl, or -20 to -40 cb potential. No significant differences existed
below 6.1 m in the amount of nitrate-N in the porous bulb sample where the
amount of water added was estimated by a combination of potential ET and
leaf area.
OBJECTIVE 3 - POTENTIAL OF USING SUBIRRIGATION FOR MORE EFFICIENT WATER
APPLICATION AND NEW SYSTEMS OF FERTILIZATION FOR LONG-RANGE SOLUTIONS TO
THE POLLUTION PROBLEM
Porous Bulb Samples
As previously discussed, some increases in nitrate-N concentrations were
noted during the 1973 growing season in the sprinkler-irrigated (Figures 90
and 93) and furrow-irrigated (Figures 91, 92, and 94) unfertilized plots.
Such major differences were not noted in the manual subirrigated (Figure 138)
or the automatically-subirrigated (Figure 139) unfertilized plots. In
general, the values were 15 ppm or less throughout the profile in both
systems.
No increases in nitrate-N in the porous bulb extracts from the control
plots in the subirrigation systems were noted between 1971 and 1973. In a
manually-subirrigated control plot (Figure 140), the nitrate-N of soil-water
extracts in 1973 were approximately equal to those obtained in 1971. In a
similar automatically-subirrigated plot (Figure 141), the nitrate-N content
of the soil-water extracts on June 4, 1973 was significantly less than the
values obtained on July 5, 1972. Problems were experienced in obtaining
extracts from some of the automatically-subirrigated plots due to the small
226
-------
D_
LU
Q
0.0
6.1.
MANUALLY-SUBIRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
20 30
NITRATE-N, ppm
40
50
Figure 138. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a control plot.
227
-------
O.Of
D_
UJ
Q
1.5
AUTOMATICALLY-SUBIRRIGATED
1 - APRIL 23, 1972
2 - MAY 8, 1972
3 - JUNE 22, 1972
4 - JULY 5, 1972
40
50
Figure 139.
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972 for a control plot.
228
-------
MANUALLY-SUBIRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 1, 1972
3 - JULY 11, 1973
0
10
40
50
20 30
NITRATE-N, ppm
Figure 140. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a control plot.
229
-------
O.Of
9.1,
Figure 141.
AUTOMATICALLY-SUBIRRIGATED
1 - JULY 5, 1972
2 - JUNE 4, 1973
10
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract m'trate-N concentrations by
soil depth during 1972-1973 for a control plot.
230
-------
amounts of water applied, and it was not possible to compare soil-water
extracts from the ends of both growing seasons. Therefore, the data from
1973 were obtained in the early part of the growing season when the nitrate-N
content was rather high due to nitrification from soil nitrogen. However, no
increases were noted in the nitrate-N of the soil-water extracts below 4.6 m.
Due to the unique method of applying water in the root zone by subirri-
gation systems, the obvious method of applying fertilizers would be through
the system itself. When Uran was applied through both the manual
(Figure 142) and automated (Figure 143) subirrigation systems in 1972 or
1973, two things were noted. High nitrate-N levels existed during the grow-
ing season in the root zone under both systems compared to the unfertilized
plots of both systems (Figures 138 and 139). Also, higher nitrate-N concen-
trations were obtained in samples obtained below the root zone (>1.5 m) in
the plots where fertilizer was applied through the irrigation water
(Figures 144 and 145) than in the unfertilized plots (Figures 140 and 141)
and the concentrations increased over the two-year period. The data thus
suggest that, although the technique is efficient relative to maintaining
high levels of nitrate-N in the root zone, much care must be taken relative
to placement of the subirrigation system and applying the fertilizers to
insure that the fertilizer is applied at the location and in the amount that
can be absorbed by the crop so that little nitrate-N remains to be lost to
irrigation return flow.
Figure 146 shows the nitrate-N concentration of the soil-water extracts
where anhydrous ammonia was banded in the bed over the manual subirrigation
system in 1973. The concentrations in the root zone were higher on June 4
in the fertilized plot (Figure 146) than the unfertilized plot (Figure 138).
Concentrations below the root zone (>1.5 m) in the fertilized plot were
higher in April and June and the same in July at the end of the growing
season than those in the unfertilized plot. Between 1971 and 1973, concen-
trations in the ammonia-fertilized plot (Figure 147) were slightly lower in
the root zone (<1.5 m) and slightly higher below the root zone (>1.5 m) than
the unfertilized plot (Figure 140).
Uran was applied in the bed in both the manual subirrigation system and
automated subirrigation system. The data from the 1972 and 1973 growing
seasons are similar to those obtained from other fertilizer treatments. For
the manual subirrigation system (Figure 148), nitrate-N concentrations of
the soil-water extracts were high in June but low in July at the end of the
season similar to the plot fertilized with anhydrous ammonia (Figure 146).
Concentrations of nitrate-N in the root zone of the automated subirrigation
plot (Figure 149) were similar to those of the unfertilized plot
(Figure 139). Below the root zone, the concentrations of nitrate-N were
higher in the Uran-fertilized plot (Figure 149) than in the unfertilized
plot (Figure 139). Between 1971 and 1973 there was a trend toward an
increase in the nitrate-N in the soil-water extracts between 3.0 and 6.1 m
in the Uran-fertilized subirrigated plots (Figures 150 and 151) as compared
to the unfertilized plots of the same systems (Figures 140 and 141). How-
ever, since the differences are only 3 to 8 ppm nitrate-N, conclusions
cannot be made concerning their significance.
231
-------
0.0
9.1
MANUALLY-SUBIRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
20
30
40
50
Figure 142.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran applied
in the irrigation water.
232
-------
o_
LU
Q
- 4.6
AUTOMATICALLY-SUBIRRI6ATED
APRIL 19, 1972
MAY 8, 1972
JUNE 22, 1972
JULY 5, 1972
40
50
20 30
NITRATE-N, ppm
Figure 143. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972 for a plot treated with Uran applied
in the irrigation water.
233
-------
CL.
LU
Q
MANUALLY-SUBIRRIGATED
1 - AUGUST 17, 1971
2 - JULY 5, 1972
3 - JULY 11, 1973
10
40
50
20 30
NITRATE-N, ppm
igure 144. Porous bulb soil-water extract m'trate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with Uran applied in the irrigation water.
234
-------
AUTOMATICALLY-SUBIRRIGATED
1 - JULY 5, 1972
2 - JUNE 25, 1973
20 30
NITRATE-N, ppm
Figure 145. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972-1973 for a plot treated with Uran
applied in the irrigation water.
235
-------
G.Oi
1.5'
3.0 •
- 4.6..
D_
UJ
a
6.1 •
7.6"
9.1
Figure 146.
MANUALLY-SUBIRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 11, 1973
10
20
30
40
50
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with ammonia
banded in the bed.
236
-------
0.0
1.5
3.0
3C
I—
LU
4.6
6.1
7.6 ?
9.1
0
MANUALLY-SUBIRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 1, 1972
3 - JULY 11, 1973
10
40
50
20 30
NITRATE-N, ppm
Figure 147. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with ammonia banded in the bed.
237
-------
o.of
1.5
3.0
" 4.6
D_
UJ
Q
6.1
7.6
9.1
0
10
MANUALLY-SUBIRRIGATED
1
2
3
4
APRIL 1, 1973
JUNE 4, 1973
JUNE 13, 1973
JULY 10, 1973
40
50
20 30
NITRATE-N, ppm
Figure 148. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with Uran banded
in the bed.
238
-------
0.0
3C
-------
0.0!
1.5
3.0
_r 4.6
Q_
UJ
Q
6.1
7.6
9.1
Figure 150.
MANUALLY-SUBIRRIGATED
1 - SEPTEMBER 3, 1971
2 - JULY 3, 1972
3 - JULY 10, 1973
10
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated with
Uran banded in the bed.
240
-------
D-
UJ
AUTOMATICALLY-SUBIRRIGATED
1 - JULY 5, 1972
2 - JUNE 20, 1973
10
20
30
40
50
Figure 151.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1972-1973 for a plot treated with Uran
banded in the bed.
241
-------
Nitrate-N content of the soil-water extracts where urea was banded in
the manual subirrigation plots (Figure 152) was only slightly higher than
the unfertilized plot (Figure 138) at 0 to 1.2 m. The major difference
between the two plots was the higher values for nitrate-N between 1.5 and
3.0 m which was below the root zone. The same was true between 1971 and
1973 for the two treatments (Figures 153 and 140). There was little differ-
ence between the two treatments in the nitrate-N concentration below 3.0 m.
Ammonia + N-Serve (Figure 154) was compared to ammonia alone
(Figure 155) during 1971. It can be seen that the N-Serve did not signif-
icantly decrease the rate at which ammonia was converted to nitrate
(Figure 154) when compared to the ammonia alone (Figure 155) or the unfer-
tilized plot (Figure 138). As previously mentioned, treatments containing
N-Serve were discontinued after the 1971 growing season.
In summary, highest values for nitrate-N in porous bulb extracts in the
root zone were obtained when Uran was ap-plied with the irrigation water.
However, significant increases in nitrate-N were also noted below the root
zone indicating that discretion should be practiced relative to the place-
ment of the irrigation pipe and the timing and amounts of Uran applied to
insure that little nitrate remains to contribute to irrigation return flow.
With the exception of a few dates, nitrate-N concentrations where the
various fertilizers were banded in the bed were only slightly higher than
the unfertilized plots. It was not possible to account for much of the
banded fertilizer.
Soil Samples
Average concentrations of nitrate-N found in 1:1 soil-water extracts of
soil samples taken at five locations laterally across the beds and down to a
depth of 6 m are shown for anhydrous ammonia, band application of Uran and
band application of sulfur-coated urea in Figures 156, 157, and 158, respec-
tively. These soil samples were taken in July of 1974 after four cropping
years, and the data obtained from the extracts are plotted against the same
type of extract from soil samples taken in 1971. The total amount of nitro-
gen applied as anhydrous ammonia was 514 kg of N/ha over the cropping period.
The total amount of nitrogen applied as Uran was 508 kg/ha and 518 kg/ha as
sulfur-coated urea. The amounts of nitrate-N found in the 1:1 soil extracts
at depths below 1.5 m were generally less than those found in 1971 where
anhydrous ammonia and sulfur-coated urea were used as the sources of nitro-
gen. This is in direct contrast to the data shown for ammonia (Figure 118),
Uran (Figure 122), and sulfur-coated urea (Figure 134) applications made to
furrow and sprinkler systems where increases in nitrate-N concentrations in
the soil profile were evident. There was some increase in nitrate-N in the
soil where Uran was banded as the source of nitrogen, and the pattern
exhibited is somewhat similar to that seen under sprinkler and furrow irri-
gation.
In summary, the low nitrate data obtained from soil samples show that
subirrigation used in conjunction with banding fertilizer applications above
the subirrigation lateral has some potential for reducing pollution hazards.
242
-------
O.Or
MANUALLY-SUBIRRIGATED
1 - APRIL 1, 1973
2 - JUNE 4, 1973
3 - JULY 10, 1973
20 30
NITRATE-N, ppm
Figure 152. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1973 for a plot treated with sulfur-coated
urea banded in the bed.
243
-------
0.0
9.1
0
MANUALLY-SUBIRRIGATED
1 - SEPTEMBER 3, 1971
2 - JUNE 12, 1972
3 - JULY 10, 1973
10
40
50
20 30
NITRATE-N, ppm
Figure 153. Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971, 1972 and 1973 for a plot treated
with sulfur-coated urea banded in the bed.
244
-------
0.0?
Q_
UJ
Q
0
MANUALLY-SUBIRRIGATED
1 - JUNE 25, 1971
2 - AUGUST 17, 1971
3 - SEPTEMBER 3, 1971
20
30
40
50
Figure 154.
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with ammonia +
N-Serve banded in the bed.
245
-------
0.0
1.5
3.0
« 4.6
re:
Q_
LJJ
Q
6.1
7.6
9.1
Figure 155.
MANUALLY-SUBIRRIGATED
1 - JUNE 25, 1971
2 - JULY 8, 1971
3 - SEPTEMBER 3, 1971
10
40
50
20 30
NITRATE-N, ppm
Porous bulb soil-water extract nitrate-N concentrations by
soil depth during 1971 for a plot treated with ammonia
banded in the bed.
246
-------
0.0
0,6
1.2
1.8
2.4
D-
LU
Q
3.0
3.6
4.3
4.9
5.5,
18
MANUALLY-SUBIRRIGATED
TREATMENT
BEFORE TREATMENT
AMMONIA
SAMPLE
DATE
- 1971
- 1974
6
8
10
12
14
16
Figure 156.
NITRATE-N, ppm
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974. (Total N - 514 kg/ha)
247
-------
o,or
0.6i
1.2
1.8
2.4
Q-
LJ
Q
3.0
3.6
MANUALLY-SUBIRRIGATED
4.3
4.9
TREATMENT
1 - BEFORE TREATMENT
2 - URAN BANDED
SAMPLE
DATE
- 1971
- 1974
5.5
12
14
16
Figure 157.
2 4 6 8 10
NITRATE-N, ppm
Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974. (Total N - 508 kg/ha)
248
-------
0.0
0.6
1.2
1.8
2.4
D-
LU
Q
3.0
3.6
4.3
4.9
5.5
0
\
MANUALLY-SUBIRRIGATED
TREATMENT
1 - BEFORE TREATMENT
2 - SULFUR-COATED UREA BANDED
SAMPLE
DATE
- 1971
- 1974
12
14
16
24 6 8 10
NITRATE-N, ppm
Figure 158. Soil extract (1:1) nitrate-N concentrations by soil depth
before treatment (1971) and after four years of N applica-
tion, 1974. (Total N - 518 kg/ha)
249
-------
Isotope (15N) Studies
As previously discussed, it was not possible to separate the
contributions of fertilizer nitrogen and soil nitrogen to the nitrogen in
the soil profile. A separate study was conducted in 1973 and 1974 to
delineate these differences. Nitrogen as sodium nitrate was applied at
two locations in each irrigation system at the rate of 123.6 kg/ha and
104.7 kg/ha in 1973 and 1974, respectively. Samples were obtained within
the profile to points where 15N could no longer be detected and analyzed
as previously described. The data were analyzed both qualitatively and
quantitatively. A discussion of the qualitative analyses follows.
Qualitative Studies--
Since much of the nitrogen determined was in the nitrate form and this
is the ion of major concern, it is the form to be discussed in this section.
The organic nitrogen determined will be discussed in the following section.
Nitrate-N from all sources (soil and fertilizer)—Total nitrate-N
determinations were made as well as ibN nitrate-N in order to obtain the
magnitude of the contribution of fertilizer nitrogen. The data shown in
Figures 159 through 164 include nitrate-N from all sources for 1973-1974.
Each data point is the weighted average of five samples. Concentrations of
nitrate-N in the sprinkler-irrigated plot (Figure 159) in 1973 were low in
May (<10 ppm), increased to 30 to 35 ppm at 0.6 m in June and decreased
again in July with the peaks occurring at 0.9 m. ,
In 1974, each plot to which 15N was applied in 1973 was split and
15N-enriched fertilizer was applied to one-half of each plot (Locations 1-1
and 2-1, Figure 160), and unenriched fertilizer was applied to the other
half (Locations 1-2 and 2-2, Figure 160). The same trend relative to
concentrations of nitrate-N in the sprinkler-irrigated plot was obtained
in 1974 (Figure 160) as in 1973 (Figure 159) in that the highest concen-
trations in the surface 0 to 0.6 m occurred in June. The peak concentration
of 5 ppm observed on July 27 in 1973 at 0.9 m apparently had moved to 2.1 to
2.7 m by the beginning of the growing season in 1974. Rainfall received
between harvest in 1973 and planting in 1974 was 33.3 cm in 27 rainfall
periods which probably accounted for this movement.
Maximum concentrations of nitrate-N from all sources observed in the
furrow-irrigated plots in May of 1973 (Figure 161) were lower than those in
the sprinkler-irrigated plots (Figure 159) and higher in the profile. Con-
centrations in samples obtained from the furrow-irrigated plots did not
exceed 20 ppm which was lower than those of the sprinkler-irrigated plots.
Peak concentrations in 1973 in the furrow-irrigated plots of 15 to 18 ppm
were observed in June at 0.6 to 0.9 m. By July 27, the peak concentrations
were at 1.2 m indicating the fertilizer moved from 0.3 m to 0.9 to 1.2 m
during the growing season. Nitrate-N concentrations in samples obtained in
July from the furrow-irrigated plots were generally higher than those
obtained from the sprinkler-irrigated plots. At the end of the growing
season, a peak concentration of 5 to 10 ppm nitrate-N was observed at 1.2 to
1.5 m compared to a similar but lower peak in the sprinkler-irrigated plots
at 0.9 m.
250
-------
ro
CJl
0.0
0.6
1.2
Q_
UJ
a
1.8
2.4
3.0
LOCATION 1
MAY 29, 1973
JUNE 13, 1973
JUNE 21, 1973
JULY 5, 1973
JULY 27, 1973
SPRINKLER-IRRIGATED
LOCATION 2
SPRINKLER-IRRIGATED
10 15 20 25
30 0 5
NITRATE-N, pprn
10 15
20
25
30 35
Figure 159. Concentrations of nitrate-N from all sources by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
ro
en
Q_
LU
Q
O.Q
0.6
1.2
1.8
2.4
3.0
3.7
4.3
4.9
5.5
6.1
LOCATION 1-1
LOCATION 1-2
1 -MAY 22, 1974
2 -JUNE 18, 1974
3 -JULY 16, 1974
SPRINKLER-IRRIGATED SPRINKLER-IRRIGATED
LOCATION 2-1
1 -MAY 23, 1974
2-JUNE 19, 1974
3-JULY 16, 1974
SPRINKLER-IRRIGATED
LOCATION 2-2
SPRINKLER-IRRIGATED
10 15 0
5 10 15 0 5 10 15 0
NITRATE-N, ppm
10 15 20
Figure 160. Concentrations of nitrate-N from all sources by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
LOCATION 1
ro
en
CO
MAY 29, 1973
JUNE 11, 1973
JUNE 22, 1973
JULY 6, 1973
JULY 27, 1973
FURROW-IRRIGATED
LOCATION 2
FURROW-IRRIGATED
10
15 20 25 30 0 5
NITRATE-N, ppm
10 15 20 25 30 35
Figure 161. Concentrations of nitrate-N from all sources by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
In 1974, concentrations of nitrate-N in the surface 2.4 m were generally
higher in the furrow-irrigated plots (Figure 162) than in the sprinkler-
irrigated plots (Figure 160). Peak concentrations of nitrate-N at the end
of the growing season at 1.2 to 1.5 m in 1973 were observed at 1.8 to 2.4 m
at the beginning of the 1974 growing season in the furrow-irrigated plots,
indicating that the peaks did not move as far in the furrow-irrigated plots
as in the sprinkler-irrigated plots (Figure 160). High concentrations of
nitrate-N were also noted in the surface 0.6 m in both the sprinkler-
figure 160) and furrow-irrigated plots (Figure 162).
As with the sprinkler- and furrow-irrigated plots, the nitrate-N concen-
trations from all sources in the subirrigated plots in 1973 (Figure 163) were
low in May, highest in June and decreased in July. Highest concentrations
were at 0.3 m in the subirrigated plots compared to 0.3 to 0.9 m in the
sprinkler- (Figure 159) and furrow-irrigated (Figure 161) plots. At the end
of the growing season (July 30), concentrations in the subirrigated plots
(Figure 163) were less than 1 ppm which was much lower than those of the
sprinkler- (Figure 159) and furrow-irrigated (Figure 161) plots.
Peak concentrations of nitrate-N from all sources in the subirrigated
plots in 1974 (Figure 164) was high at 0.3 m (15 to 29 ppm) and decreased
sharply with depth so that concentrations below 0.6 m were generally less
than 2 ppm, which was less than those of the sprinkler- and furrow-irrigated
plots.
Nitrate-N from fertilizer—As discussed initially, the primary concern
of this study was to determine the fate of fertilizer nitrogen. As with
nitrogen from all sources, relatively high concentrations of fertilizer
nitrate-N were found in the sprinkler-irrigated plots in June in 1973
(Figure 165) following the sidedress application of fertilizer on June 4.
Concentrations decreased as the season progressed so that low concentrations
of fertilizer nitrate-N existed in the soil at the end of the growing season.
No fertilizer nitrate-N was located below 0.9 m at the end of the growing
season.
At the beginning of the 1974 season (Figure 166), concentrations of
fertilizer nitrate-N were noted at 2.4 to 2.7 m indicating some movement
during the period when a crop was not growing. The concentrations are too
low (<5 ppm) to be of concern. However, if an excess of nitrate-N from
fertilizer would have been available, the data indicate that it would have
moved from 0.9 m to 2.7 to 3.0 m from the 33.3 cm of rainfall received
between the 1973 and 1974 growing seasons.
It is notable that insignificant amounts of fertilizer nitrate-N were
found in the root zone of the subplots (Locations 1-2 and 2-2, Figure 166)
which were not fertilized with 15N-enriched fertilizer in 1974. Further,
high concentrations of fertilizer nitrate-N were not observed in the plots
treated with 15N-enriched fertilizer in 1974 indicating that if recommended
rates of fertilizer are used, concentrations within the profile can be kept
at levels which will not be of concern.
254
-------
LOCATION 1-1
en
LOCATION 1-2
LOCATION 2-1
LOCATION 2-2
1 - MAY 16, 1974
2 - JUNE 14, 1974
3 - JULY 18, 1974
FURROW-IRRIGATED
FURROW-IRRIGATED
FURROW-IRRIGATED
i i »
1 - MAY 17, 1974
2 - JUNE 17, 1974
3 - JULY 19, 1974
FURROW-IRRIGATED
*
0 5
Figure 162.
10
15
10 15 0 5
NITRATE-N, ppm
10 15
10
15
20
Concentrations of nitrate-N from all sources by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
0.0
r>o
in
en
0.6
1.2
E
f\
•zz
UJ
Q
1.8
2.4
3.0
LOCATION 1
MAY 29, 1973
JUNE 13, 1973
JUNE 21, 1973
JULY 6, 1973
JULY 30, 1973
SUBIRRIGATED
LOCATION 2
SUBIRRIGATED
10 15 20 25 30 0 5
NITRATE-N, ppm
10 15 20 25 30 35
Figure 163. Concentrations of nitrate-N from all sources by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
LOCATION 1-1
IX)
en
1 -MAY 16, 1974
2-JUNE 14, 1974
3 -JULY 18, 1974
SUBIRRIGATED
LOCATION 1-2
SUBIRRIGATED
LOCATION 2-1
1 -MAY 17, 1974
2-JUNE 17, 1974
3-JULY 19, 1974
SUBIRRIGATED
LOCATION 2-2
SUBIRRIGATED
10 15 0
10 15 0 5 10 15 0
NITRATE-N, ppm
10 15 20
Figure 164. Concentrations of nitrate-N from all sources by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
LOCATION 1
en
00
1.2
LOCATION 2
t r i
IM i
Q I 2
1.8 ? 3
4
5
2.5*
- MAY 29, 1973
- JUNE 13, 1973
- JUNE 21, 1973
- JULY 5, 1973
- JULY 27, 1973
SPRINKLER-IRRIGATED
i n t i
k
^
'
SPRINKLER-IRRIGATED
t T i t inini-tt
10 15 20 25 30 0 5
NITRATE-N, ppm
10
15
20
25
30
35
Figure 165. Concentrations of fertilizer nitrate-N by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
0.0 LOCATION 1-1
rv>
en
D_
LU
Q
LOCATION 1-2
3.0
3.7
4.3
4.9
5.5
6.1
0
Figure
LOCATION 2-1
LOCATION 2-2
j 1 - MAY 22, 1974
j 2 - JUNE 18, 1974
3 3 - JULY 16, 1974
]
3
SPRINKLER-IRRIGATED
P
I
1
1
3
1
SPRINKLER-IRRIGATED
j 1 - MAY 23, 1974 t
j 2 - JUNE 19, 1974 !
3 3 - JULY 16, 1974
3
3
SPRINKLER-IRRIGATED
a
3
3
3
SPRINKLER-IRRIGATED
166.
0
NITRATE-N, ppm
Concentrations of fertilizer nitrate-N by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
10
-------
As with the nitrate-N from all sources, the fertilizer nitrate-N
concentrations in the furrow-irrigated plots in 1973 (Figure 167) were not
as high as in the sprinkler-irrigated plots (Figure 165). Concentrations
were 10 ppm or less in the furrow plots compared to 30 ppm in the sprinkler
plots. Also, concentrations of fertilizer nitrate-N were located deeper
within the profile (1.2 to 1.5 m) of the furrow-irrigated plots than the
sprinkler-irrigated plots (0.9 m) at the end of the growing season.
In 1974, a major difference between the furrow-irrigated plots
(Figure 168) and the sprinkler-irrigated plots (Figure 166) was the large
amount of fertilizer nitrate-N detected in the 1.2 to 2.4 m zone. Differ-
ences in the concentrations of nitrate-N from all sources in all furrow
plots were not great (Figure 162) but'Significant differences existed in the
amount of fertilizer nitrate-N in plots fertilized with 15N-enriched fertil-
izer in 1974 (Locations 1-1 and 2-1) and those fertilized with unenriched
fertilizer (Locations 1-2 and 2-2). These data indicate that nitrogen
applied as fertilizer in 1974 leached into the 1.2-to2.4-m zone.
Concentrations of fertilizer nitrate-N in the subirrigated plot
(Figure 169) followed a pattern similar to that of nitrate-N from all
sources in that the concentrations below 0.6 m were significantly lower in
the subirrigated plots (Figure 169) than in the sprinkler- (Figure 165) and
furrow-irrigated (Figure 167) plots.
In 1974, significant amounts of fertilizer nitrate-N applied in 1973
were not detected in subirrigated plots (Figure 170) which were not fertil-
ized with 15N-enriched fertilizer in 1974. As will be discussed in detail
later, this is ideal from the standpoint of irrigation return flow. With
the exception of the concentrations at 0.3 m, the values for fertilizer
nitrate-N of the subirrigated plots fertilized with 15N-enriched nitrogen in
1974 (Locations 1-1 and 2-1) were significantly lower in the subirrigated
plots (<1 ppm, Figure 170) than in the sprinkler-irrigated (Figure 166) or
the furrow-irrigated plots (Figure 168) and were too low to be of concern.
Percent nitrate-N as fertilizer nitrogen--Since the nitrate-N levels of
the ljN-fert11ized plots were relatively low, it was difficult to get a feel
for the potential pollution problem by nitrate-N from fertilizer. It was
therefore decided to view the percent of nitrate-N that was fertilizer
nitrate-N since percentages would better emphasize the contributions of
fertilizer than the low concentrations.
In the sprinkler-irrigated plot in 1973 (Figure 171), the maximum
percentages of fertilizer nitrate-N (80% to 90%) were obtained at 0.6 m in
June with lower values above and below this depth. At the end of the
season, the maximum value (25% to 40%) was obtained at 0.9 m. The data
thus show that a high percentage of the nitrate-N in the root zone was from
the fertilizer and that insignificant amounts had moved below the root zone
during the growing season.
At the beginning of the 1974 season, over 75% of the nitrate-N at 2.4
to 3.0 m was from fertilizer in the sprinkler-irrigated plots (Figure 172).
Since actual concentrations were low, the amounts present were not
260
-------
ro
CTl
D-
UJ
o
1.8
2.4
3.0
LOCATION 1
MAY 29, 1973
JUNE 11, 1973
JUNE 22, 1973
JULY 6, 1973
JULY 27, 1973
FURROW-IRRIGATED
LOCATION 2
FURROW-IRRIGATED
10 15 20 25 30 0 5
NITRATE-N, ppm
10
15
20
25
30
35
Figure 167. Concentrations of fertilizer nitrate-N by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
ro
en
ro
0,0r LOCATION 1-1
0.6
3 - JULY 18, 1974
LOCATION 1-2
LOCATION 2-1
FURROW-IRRIGATED
LOCATION 2-2
MAY 17, 1974
JUNE 17, 1974
JULY 19, 1974
FURROW-IRRIGATED
FURROW-IRRIGATED
Figure 168.
5 05 0505
NITRATE-N, ppm
Concentrations of fertilizer nitrate-N by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
10
-------
0.0
LOCATION 1
no
CTl
CO
1.2
LOCATION 2
:r I
Q-
LxJ
Q
1.8 '
*
I
2.4 '
0 5
Figure 169.
1 - MAY 29, 1973
2 - JUNE 13, 1973
3 - JUNE 21, 1973
4 - JULY 6, 1973
5 - JULY 30, 1973
SUBIRRI GATED
e
r
£
*
SUBIRRIGATED
f(filtr-T'--f
10 15 20 25 30 0 5 10 15 20 25 30 35
NITRATE-N, ppm
Concentrations of fertilizer nitrate-N by depth in 1973 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
0.0
LOCATION 1-1
ro
cr>
LOCATION 1-2
LOCATION 2-1
5.5
6.1
•' 0
1 - MAY 16, 1974
2 - JUNE 14, 1974
3 - JULY 18, 1974
SUBIRRIGATED
SUBIRRIGATED
LOCATION 2-2
1 - MAY 17, 1974
2 - JUNE 14, 1974
3 - JULY 19, 1974
.
SUBIRRIGATED
SUBIRRIGATED
5 0
NITRATE-N, ppm
10
Figure 170. Concentrations of fertilizer m'trate-N by depth in 1974 for plots treated with
15N-enriched sodium nitrate banded in the bed.
-------
0.0
LOCATION 1
ro
cr>
en
D-
LU
Q
LOCATION 2
Figure 171.
MAY 29, 1973
JUNE 3, 1973
JUNE 21, 1973
JULY 5, 1973
JULY 27, 1973
SPRINKLER-IRRIGATED
SPRINKLER-IRRIGATED
20
40
60
20
40
60
80
100
80 0
FERTILIZER-N, %
Percent nitrate-N from fertilizer by depth in 1973 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
0.0
LOCATION 1-1
ro
cr>
Q.
UJ
Q
1 - MAY 22, 1974
2 - JUNE 18, 1974
3 - JULY 16, 1974
SPRINKLER-IRRIGATED
LOCATION 1-2
LOCATION 2-1
LOCATION 2-2
SPRINKLER-IRRIGATED
1 - MAY 23, 1974
2 - JUNE 19, 1974
3 - JULY 16, 1974
SPRINKLER-IRRIGATED
SPRINKLER-IRRIGATED
0 25 50 75 0 25 50 75 0 25 50 75 0 25 50 75 100
FERTILIZER-N, %
Figure 172. Percent nitrate-N from fertilizer by depth in 1974 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
significant (Figure 166). However, if an excess had been applied, a
significant amount of fertilizer nitrate-N would have been located at this
depth.
In the furrow-irrigated plot in 1973 (Figure 173), up to 60% of the
nitrogen present in the nitrate form in the root zone was from fertilizer.
This was not as high as in the sprinkler-irrigated plot (Figure 161) but it
was spread over a wider band. At the end of the season (July 27, 1973),
40% to 50% of the nitrate-N present at 0.9 to 1.2 m was fertilizer nitrogen
which was much higher than in the sprinkler-irrigated plot. Again, the
concentrations were small (Figure 167).
The same trend carried into the 1974 season in the furrow-irrigated
plot (Figure 174). As much as 50% of the nitrate-N at 1.5 to 2.1 m was from
fertilizer at the beginning of the season (May 16). As the season pro-
gressed, the percentages decreased or remained approximately the same and
moved to depths of 2.4 to 4.3 m by July 19, 1974, indicating movement of
nitrate-N from fertilizer applied in 1973 in the furrow-irrigated plots
which did not occur in the sprinkler-irrigated plots (Figure 172).
Fertilizer nitrate-N percentages as high as 60 were noted in the subir-
rigated plots in the surface 0.6 m (Figure 175). In general, percentages
below this depth were 20 or less which was much lower than those found in
the sprinkler- (Figure 171) or furrow-irrigated plots (Figure 173) at
similar depths. Again, the concentrations in the subirrigated plots were
low (Figure 170).
In 1974, the percentages at Location 1-1 in the subirrigated plot
(Figure 176) approached 50 at almost all depths in the surface 3.3 m. How-
ever, the concentrations at these depths with the exception of the 0.3-m
depth were generally less than 2 ppm (Figure 170) so the values are of no
major concern. It does point out, however, the possibility of major leach-
ing of fertilizer nitrate-N during the growing season if excess amounts are
present.
Summary—Differences in concentrations of nitrate-N from all sources,
fertilizer nitrate-N and percent nitrate-N from fertilizer differed among
the sprinkler, furrow, and subirrigation systems during the two years of the
study. Highest concentrations from all sources in 1973 were obtained in the
sprinkler plots followed by the furrow and subirrigation plots. With the
exception of the surface 0.6 m, little nitrate-N was found in the subirri-
gation system while significant concentrations were found down to 1.2 m in
the sprinkler and furrow systems.
Leaching of nitrate-N from all sources from 0.9 m to 2.7 m apparently
occurred in the sprinkler system between the 1973 and 1974 growing seasons.
Some leaching was noted in the furrow systems with none being noted in the
subirrigation systems. Significantly higher nitrate-N concentrations were
noted in the furrow systems between 1.2 and 2.4 m than in the sprinkler and
subirrigation systems showing more leaching below the root zone during the
growing season.
267
-------
0.0
LOCATION 1
ro
oo
0.6
a.
LU
Q
LOCATION 2
MAY 29, 1973
JUNE 11, 1973
JUNE 22, 1973
JULY 6, 1973
JULY 27, 1973
FURROW-IRRIGATED
FURROW-IRRIGATED
40
60
80 0
FERTILIZER-N,
20
40
60
80
100
Figure 173. Percent nitrate-N from fertilizer by depth in 1973 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
en
0.0
0.6
1.2
1.8
2.4
Q.
UJ
Q
3.7
4.3
4.9
5.5
6.1
LOCATION 1-1
LOCATION 1-2
LOCATION 2-1
LOCATION 2-2
1 - MAY 16, 1974 fi\l
2 - JUNE 14, 1974
I 3 - JULY 18, 1974
FURROW-IRRIGATED
FURROW-IRRIGATED
3 - JULY 19, 1974
FURROW-IRRIGATED
0 25 50 75 0 25 50 75 0 25 50 75 0 25 50 75 100
FERTILIZER-N, %
Figure 174. Percent nitrate-N from fertilizer by depth in 1974 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
0.0
ro
•^j
o
0.6
1.2
1.8
2.4
3.0
20
LOCATION 1
MAY 29, 1973
JUNE 13, 1973
JUNE 21, 1973
JULY 6, 1973
JULY 30, 1973
SUBIRRIGATED
LOCATION 2
SUBIRRIGATED
40
60
20
40
60
80
100
Figure 175.
80 0
FERTILIZER-N, %
Percent nitrate-N from fertilizer by depth in 1973 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
Q-
LU
0.0,
0.6|
1.2,
1.8,
2.4i
3.0
3.7
4.3
4.9
5.5
6.1
LOCATION 1-1
1 -MAY 16, 1974
2- JUNE 14, 1974
3- JULY 18, 1974
SUBIRRIGATED
LOCATION 1-2
SUBIRRIGATED
LOCATION 2-1
LOCATION 2-2
1 -MAY 17, 1974
2- JUNE 17, 1974
3-JULY 19, 1974
SUBIRRIGATED
SUBIRRIGATED
0 25 50 75 0 25 50 75 0 25 50 75 0 25 50 75 100
FERTILIZER-N, %
Figure 176. Percent nitrate-N from fertilizer by depth in 1974 for plots treated with 15N-enriched
sodium nitrate banded in the bed.
-------
Analyses of data showing the contribution of fertilizer nitrogen to soil
nitrate-N further supported the conclusions that leaching of fertilizer
nitrogen occurred between seasons in the sprinkler-irrigated plot, during
the season in the furrow-irrigated plot, and all but disappeared from the
subirrigated plot that was not fertilized with 15N-enriched fertilizer in
1974.
Data on the percentage of fertilizer nitrate-N emphasized the potential
pollution from the various systems. Over 50% of the nitrogen at 2.4 to 3.0 m
in the sprinkler plot at the beginning of the 1974 season and at 1.5 to 3.0 m
in the furrow-irrigated plots during the growing season was fertilizer nitro-
gen, thus indicating a strong possibility that irrigation return flows with
these systems can be degraded by fertilizer nitrogen even with good irriga-
tion and fertilization practices.
Fertilizer nitrate-N percentages were high in one of the subirrigated
plots but concentrations were too low to be of concern. However, the possi-
bility of some leaching losses from subirrigation systems was found to be
possible. The extremely low values obtained with the subirrigation system
will be discussed in more detail in another section.
Leaching losses were found to be possible, especially with the furrow
and sprinkler irrigation systems. However, the low concentrations obtained
indicated that unless excess amounts of nitrogen are present when leaching
occurs, the losses will be minimal.
Quantitative Studies--
At the end of two crop years (1973 and 1974), it was possible to account
for 92.6%, 86.1%, and 50.5% of the fertilizer nitrogen applied to the sprin-
kler, furrow, and subirrigation systems, respectively. These calculations
were based on fertilizer nitrogen found in above ground plant samples
(Table 24) and soil samples taken to 5.2 m (Table 25). Soil samples were
taken in 30-cm depth increments at five locations laterally across the beds
as previously described. A weighted average was obtained for each depth
using the relative contribution of each lateral sample to a given horizontal
soil layer 30-cm thick. Actual bulk densities were used in converting to
kilograms per hectare.
Fertilizer was applied to the plots used in this study for the first
time in 1973 during the course of this project. That year, the greatest
quantity of fertilizer nitrogen was taken up on the sprinkler plots and least
on the subirrigated plots (Table 26). While this resulted in a substantially
greater percentage of fertilizer nitrogen being incorporated into plant
material in sprinkler than subirrigated plots, as a percentage of total
nitrogen in the crop, there were no differences. Plant residue from the
1973 crop was returned to the soil.
Total fertilizer nitrogen recovered from fertilizer applied in both 1973
and 1974 in the above ground plant material by the 1974 crop was 56.5, 72.4,
and 62.9 kg/ha which represented 62.2%, 55.2%, and 49.3% of the total
nitrogen taken up for the sprinkler, furrow, and subirrigation systems,
respectively. The breakdown of the source of this fertilizer nitrogen is
272
-------
TABLE 24.
1974
Date
May 22
June 18
June 25
July 17
May 22
June 18
June 25
July 17
May 20
June 19
June 25
July 17
May 21
June 20
June 25
July 17
May 16
June 13
June 25
July 18
May 17
June 14
June 25
July 19
PLANT GROWTH AND NITROGEN DATA FOR THE TOP GROWTH OF SPRINKLER-IRRIGATED
FERTILIZED TWO YEARS WITH 15N-ENRICHED SODIUM NITRATE, 1974
Plant
Grain
Trt4- a 1
iota I
Plant
Grain
Total
Plant
Grain
Total
Plant
Grain
Total
Plant
Grain
Total
Plant
Gra i n
Total
Plant wt,
9
0.68
44.57
67.64
110.58
18.49
129.07
1.19
66.14
102.51
99.14
70.97
170.11
0.75
47.50
153.64
59.74
2TI738
1.00
147.13
96.15
110.76
56.21
166.97
0.50
24.67
76.74
75.45
62.47
137.92
0.48
24.53
68.45
246.22
126.13
372.35
Total N,
2.10
2.02
1.72
1.04
1.75
2.30
1.65
1.38
1.24
1.76
3.06
1.94
SAMP
1.17
2.06
3.05
2.04
1.66
1.48
2.20
2.40
1.75
1.54
0.98
1.51
2.40
1.80
1.76
1.01
1.70
N/plant,
g
Plot 6
0.014
0.901
1.160
1.149
0.324
Plot 6
0.027
1.094
1.419
1.233
1.251
Plot 18
0.022
0.920
1 £ LOS
1.795
1.232
Plot 18
0.031
2.999
1.596
1.642
1.237
Plot 32
0.012
0.431
1.183
0.742
0.945
Plot 32
0.011
0.442
1.202
2.481
2.144
Total N,
kg/ha
- Location 1
0.643
41.396
53.296
52.791
14.885
67.676
- Location 2
1.240
50.264
65.196
56.651
57.480
114.131
- Location 1
0.977
40.851
T IN D
79.705
54.708
134.413
- Location 2
1.354
133.169
70.869
72.912
54.929
127.841
- Location 1
0.485
17.410
47.787
29.972
38.175
68.147
- Location 2
0.444
17.854
48.554
100.222
_86.610
1 86 . 832
N from
fertilizer,
41.97
76.54
78.24
75.59
76.25
41.81
55.37
60.42
53.20
54.99
48.63
52.28
R Y I N G
60.44
64.04
36.41
59.76
60.94
50.32
45.47
21.65
33.58
53.67
39.95
34.15
37.05
43.41
67.86
53.96
53.39
SWEET CORN GRi
N from
fertil izer,
kg /ha
0.270
31.685
41.698
39.906
11.346
51.252
0.515
27.832
39.390
30.139
31.606
0.470
21.358
48.171
35.034
83.205
0.493
79.587
43.187
36.691
24.976
61.667
0.101
5.846
25.648
11.973
13.413
25.391
0.168
7.750
32.950
54.085
46.245
i UU . ojU
OWN ON PLOTS
N from
soil ,
kg/ha
0.373
10.349
11.592
12.891
3.539
16.430
0.717
22.445
25.816
29.882
25.872
0.504
19.477
31.539
19.678
¥17217
0.862
53.581
27.664
36.243
29.960
66.203
0.381
11.558
22.154
18.010
24.763
42.773
0.280
10.114
15.613
46.144
40.365
ob . buy
273
-------
TABLE 25. FERTILIZER NITROGEN FOUND IN TWO NITROGEN FRACTIONS OF SOIL
SAMPLES FROM PLOTS FERTILIZED TWO YEARS WITH 15N-ENRICHED
SODIUM NITRATE AND CROPPED WITH SWEET CORN IRRIGATED BY
THREE SYSTEMS, LOCATION 1
Sample
depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
3.4
3.7
4.0
4.3
4.6
4.9
5.2
Total
Sprinkler
NOZ-N Organic N
4.0 42.2
19.7 21.2
16.8 9.4
7.2 13.0
2.0
1.2
2.1
4.1
10.8
14.0
6.6
1.6
0.6
0.2
0.0
0.0
0.0
90.9 85.8
Irrigation system
Furrow
NO~-N Organic N
L'n/hn
ky/nu
7.6 15.3
15.9 3.4
10.4 0.8
18.5 12.1
11.0
8.7
16.4
16.2
6.4
2.0
0.5
0.0
0.0
0.0
0.0
0.0
0.0
113.6 31.6
Subirrigation
NO~-N
7.3
0.8
0.2
0.8
0.6
2.0
2.3
2.3
0.7
3.0
4.1
3.0
1.6
1.0
1.5
1.2
0.8
33.2
Organic N
11.1
1.5
6.2
0.6
19.4
given in Table 27. The percent of total nitrogen in the 1974 crop that was
applied as fertilizer in 1973 ranged from 2.0%, 3.6%, and 7.4%, respectively,
for the furrow, sprinkler, and subirrigation plots. The large differences
between irrigation systems observed in fertilizer nitrogen incorporated into
above ground plant material in 1973 were not found in 1974. Also, in
contrast to 1973, substantial differences were found between irrigation
systems with respect to the percentage of the total nitrogen in the crop
that was from the 1974 fertilizer application.
Examples of plant growth and nitrogen uptake patterns are shown in
Figures 177, 178, and 179, respectively, for a sprinkler plot in 1973 and a
subirrigation plot in 1973 and 1974. The uptake and growth curves are
typical for growth and nitrogen uptake. The curves were different between
years probably due to differences between hybrids and growing seasons.
The largest differences between irrigation systems in accounting for the
fertilizer nitrogen applied during the two years occurred in the soil rather
274
-------
TABLE 26. PLANT GROWTH AND NITROGEN DATA FOR THE TOP GROWTH OF SPRINKLER-IRRIGATED SWEET CORN FERTILIZED
WITH 15N-ENRICHED SODIUM NITRATE, 1973
1973
Date
May 21
May 29
June 13
June 21
July 5
July 30
Population:
May 21
May 29
June 13
June 22
July 5
July 30
Population:
May 21
May 29
June 1 1
June 22
July 6
July 30
Population
May 21
May 29
June 11
June 22
July 5
July 30
Population
May 21
May 29
June 13
June 21
July 5
July 30
Population
May 21
May 29
June 13
June 21
July 5
July 30
Population
Plant wt,
g
Plant
Grain
Total
62,900
Plant
Grain
Total
: 66,900
Plant
Grain
Total
: 58,600
Plant
Grain
Total
: 55,900
Plant
Grain
Total
: 61,000
Plant
Grain
Total
i: 55,900
0.68
3.38
57.25
88.75
133.53
107.55
60.84
168.39
plants/ha
0.76
3.41
62.48
99.79
145.73
116.32
67.45
183.77
plants/ha
1.31
2.82
61.84
92.68
169.96
138.26
69.48
plants/ha
0.88
2.15
49.22
69.69
135.27
108.92
56.25
plants/ha
0.63
3.39
51.33
93.97
123.03
114.12
66.25
180.37
plants/ha
0.72
4.71
44.94
54.18
128.13
101.80
55.77
157.57
plants/ha
Total N,
%
2.
1.
1.
1.
1.
1.
1.
2.
2.
2.
1.
1.
1.
09
97
92
23
00
07
84
90
50
50
63
23
08
1.87
1.
.48
2.60
1.87
1.81
0.69
0.91
2.02
1
2
2
1
0
0
1
2
2
2
1
1
0
1
2
2
2
2
1
0
1
.94
.45
.10
.68
.95
.91
.84
.70
.21
.25
.40
.48
.83
.60
.50
.53
.23
.50
.10
.86
.76
N/plant,
g
0.
0.
1.
1.
1.
1.
1.
0.
0.
1.
1.
1.
1.
1.
0.
0.
1.
Plot
014
067
099
092
335
151
195
Plot
022
085
612
627
792
256
261
Plot
019
073
156
1.677
1.727
1.258
1.403
Plot
0.017
0.053
1.034
1.171
1.285
0.991
1.035
Plot
0.017
0.075
1.155
1.316
1.821
0.947
1.060
0
0
1
1
1
0
0
Plot
.018
.119
.002
.354
.409
.875
.982
N from
Total N, fertilizer,
kg/ ha %
6 - Location 1
0.897
4.185
69.102
68.625
83.944
72.345
70.375
142.720'
6 Location 2
1.478
5.706
107.834
108.810
119.908
84.038
84.373
168.411
18 - Location 1
1 1.137
4.294
67.742
98.269
101.180
73.706
82.218
155.924
18 - Location 2
0.955
2.944
57.756
65.424
71.810
55.387
57.835
32 - Location 1
1.043
4.567
70.429
80.229
111.038
57.763
64.642
109 Anc;
1 L.L. . tUJ
32 - Location 2
1.011
6.661
56.002
75.688
78.756
48.922
54.851
103.773
67.
90.
77.
67.
79.
65.
59.
60.
94.
66.
79.
86.
72.
58.
35.
59.
74.
68
64
86
74
28
94
67
91
56
71
71
12
28
69
19
31
51
69.25
71.
61
75.21
69.76
0.59
74.46
71.61
78.53
46.20
69.33
62.08
79
80
51
58
59
67
62
74
72
49
68
53
71
61
.71
.83
.98
.27
.21
.88
.01
.25
.77
.64
.12
.08
.17
.97
N from
fertil izer,
kg/ha
0.607
3.793
53.803
46.487
66.550
47.704
41.993
89.697
0.900
5.395
71.935
86.733
103.265
60.743
49.519
110.262
0.400
2.547
50.475
68.051
72.455
55.434
57.355
112.789
0.006
2.193
41.359
51.377
33.177
38.400
35.904
74.304
0.831
3.692
36.609
46.750
65.746
39.209
40.085
79.294
0.750
4.847
27.800
51.559
41.804
34.817
33.991
68.808
N from
soil ,
kg/ha
0.290
0.392
15.289
22.139
17.394
24.641
28.382
53.023
0.323
0.310
35.898
22.077
16.643
23.295
34.854
58.149
0.737
1.747
17.267
30.218
28.725
18.272
24.863
43.135
0.950
0.752
16.397
14.046
38.634
16.987
21.931
38.918
0.213
0.876
33.821
33.480
45.293
18.554
24.557
437TTT
0.260
1.813
28.203
24.129
36.952
14.104
20.860
34.964
275
-------
TABLE 27. FERTILIZER NITROGEN DATA FOR THE TOP GROWTH OF TWO CROPS OF IRRIGATED SWEET CORN FERTILIZED
WITH 15N-ENRICHED SODIUM NITRATE*
1973 Crop
Fertilizer
ro
en
Irrigation
system
Sprinkler
Furrow
Subirrigation
kg/ha
100.0
93.5
74.0
of°N
applied
80.9
75.6
59.8
N
of N
in crop
64.3
69.5
65.6
1974
1973 Fertilizer N
kg/ha
3.0
3.7
6.3
of°N
applied
2.4
3.0
5.1
of°N
in crop
2.0
3.6
7.4
1974 Fertilizer N
kg/ ha
53.5
68.7
56.6
of' N
applied
51.0
65.5
54.0
of N
in crop
58.8
52.4
44.4
* 123.7 Ibs of N as sodium nitrate applied in 1973.
104.9 Ibs of N as sodium nitrate applied in 1974.
-------
200 ~
01
160 -
120
ro
Di
O
•M
C
03
80
cc
Q
40
0
• - PLANT WEIGHT
A - TOTAL N
O - FERTILIZER N
10
Figure 177.
20
30
40 50
DAYS AFTER PLANTING
60
70
80
Dry matter production, total nitrogen, and fertilizer nitrogen in the tops of sprinkler-
irrigated sweet corn fertilized with 15N-enriched sodium nitrate, 1973.
-------
200
IN3
^•J
00
;160
•=£.
^120
•4-J
C
fl3
80
E
CD
22 40 h
O
A -
O -
'10
Figure 178.
20
30
PLANT WEIGHT
TOTAL H
FERTILIZER H
I.....
40 50
DAYS AFTER PLANTING
60
70
80
90
Dry matter production, total nitrogen, and fertilizer nitrogen in the tops of subirrigated
sweet corn fertilized with 15N-enriched sodium nitrate, 1973.
-------
350 r
t\>
280-
01
I
3
a.
210
140
c
ro
_' 70
D;
• - PLANT WEIGHT
A- TOTAL N
O - FERTILIZER N
10
Figure 179.
20
30
40
DAYS AFTER PLANTING
Dry matter production, total nitrogen, and fertilizer nitrogen in the tops of subirrigated
sweet corn fertilized with 15N-enriched sodium nitrate, 1974.
-------
than the plants (Tables 25 and 27). Nitrate concentration peaks were found
in the profile immediately above layers in which abrupt increases in sand
percentages and/or lower bulk densities occurred. Particle-size distribu-
tions and bulk densities can be seen in Figures 10, 11, and 12, with discus-
sion of effects on hydraulic conductivities beginning on page 39. For the
sprinkler system, 176.7 kg of nitrogen/ha were found in the soil profile down
to 5.2 m with 90.0 kg/ha as nitrate and 85.8 kg/ha as organic nitrogen. A
significant amount of fertilizer nitrogen, 41.2 kg/ha, or 18% of that
applied, was found below 1.5m which is considered to be below the effective
root zone for the crop grown. The amount of fertilizer nitrogen found in the
soil under furrow irrigation was 145.2 kg/ha with 113.6 kg/ha nitrate and
31.6 in organic forms. While the total amount was less than that under
sprinkler irrigation, more was in the nitrate form and more, 50.2 kg/ha, or
22% of that applied, was found below 1.5m. Under subirrigation, much less
fertilizer nitrogen was found in the soil profile. To a profile depth of
5.2 m, 52.6 kg of nitrogen/ha were found with 33.2 kg/ha as nitrate and
19.4 kg/ha as organic nitrogen. In addition, lesser amounts of fertilizer
nitrogen, 23.5 kg/ha or 14.5% of applied, were found below 1.5 m. One inter-
esting phenomena was the declining amount of fertilizer nitrogen found in
organic forms in the irrigation system order of sprinkler > furrow > subirri-
gation. These data show irrigation return flow quality for these irrigation
systems, as measured by fertilizer nitrate-N, to be in the order: subirri-
gation > sprinkler > furrow.
Since the amount of fertilizer nitrogen recovered in the plant material
in 1974 for the subirrigation system was comparable to that of the other
systems, the low percentage accountability for this system was a result of
not finding the nitrogen in the soil. Nitrate-N concentrations under subir-
rigation have been low throughout this study when fertilizer was banded.
Because of this, an independent study involving intensive sampling and
bromide and nitrate fertilizer was conducted. This study is reported in
the experimental section. All the available data point to the conclusion
that the measurements are correct and that the soil profile under subirri-
gation contains less fertilizer nitrogen and the irrigation return flow will
be of better quality from the standpoint of applied fertilizer than under
sprinkler and furrow irrigation.
Disappearance of Nitrate From Subirrigated Plots
During the first two years of the project, relatively large amounts of
nitrate-N were measured in the soil-water extracts from samples where the
fertilizer was applied in the irrigation water in the subirrigated plots.
However, in the control plots and in plots where fertilizer was banded above
and to either side of the subirrigation lateral, only small amounts of
nitrate-N were detected. Initially, it was thought that nitrate was not
detected in these plots because of inadequate sampling. This may have been
true for the samples taken early in the growing season, but other data
obtained show this is not true for samples taken late in the season.
A preliminary study was conducted in 1972 to obtain data relative to
the sampling technique on all three irrigation systems. In this particular
study, sodium bromide was used along with sodium nitrate chiseled into both
280
-------
sides of the beds, as previously described and intensive samples taken every
12.7 cm laterally across the beds and down to a depth of 2.1 m. Data from
these samples are given in Tables 28 through 39. In comparing the data in
Tables 28 through 33, it is easy to see that concentrations of nitrogen were
generally lower in the subirrigated plots (0 to 6.3 ppm, Tables 32 and 33)
than the sprinkler- (0 to 27.7 ppm, Tables 28 and 29) or furrow- (0 to
12.8 ppm, Tables 30 and 31) irrigated plots. Also, the highest concentra-
tions of nitrate-N in the sprinkler and furrow plots occurred at depths of
1.2 and 1.5 m whereas for the subirrigated plot highest concentrations
occurred in the top 0.6 m of the profile. The bromide data in Tables 34
through 39 confirm the nitrate distribution found in the previous tables. It
will be noted that for the subirrigated plots the concentrations of bromide
were less than 1 ppm below 0.9 m and that concentrations up to 31 ppni occurred
in the upper portion of the profile. It is of interest to note that in the
sprinkler-irrigated plot (Table 28, Location 1) where the nitrate-N concen-
trations were generally low, the bromide concentrations show that nitrate did
not move below a depth of 0.9 m (Table 34). Consequently, the nitrate
applied with the bromide was probably taken up by the plants. These results
for nitrate-N were typical of those obtained from the profiles of the various
irrigation systems when fertilizer was banded and the measurements were made
at the end of the season.
In addition to this test conducted in 1972, another test was conducted
with a second crop. The soil-water extracts from porous bulbs for this crop
are shown in Table 40. Cross-sectional samples from the top of one bed to
the top of the next bed were taken at various dates after the application of
fertilizer and while a crop was growing. Fertilizer was applied as a band
12.7 cm either side of the bed on July 27. A 76.2-mm irrigation was applied
and the crop was planted. First measurements were made on July 28 and
nitrate was found primarily in planes B and C. Subsequent samples taken on
August 14 showed extremely high concentrations of nitrate-N in the top 45 cm
of the profile in planes A, B, C, and D. Overall, concentrations tended to
decrease in the top 45 cm until the last sampling date on October 2 in which
all concentrations with the exception of one sample in the bottom of the
furrow showed relatively low concentrations of nitrate-N compared to
previous samples.
These data taken in conjunction with the data shown in Figures 180
through 182 for a 15N tracer study conducted in 1973 show that the nitrogen
applied as fertilizer in bands tended to move down the most in the sprinkler
system early in the season, somewhat less in the furrow system and that the
nitrate-N tended to remain in the upper portions of the profile for the
subirrigation system.
Differences in the plant nitrogen uptake and growth curves (Figures 177,
178, and 179) showed less mid-season nitrogen uptake and growth by the subir-
rigated plots. However, the data in Tables 24 and 26 showing the total
amount of fertilizer nitrogen taken up by the plants in both 1973 and 1974
again show little difference between systems in that the variations within a
plot were generally as great or greater than the variations between irriga-
tion systems.
281
-------
TABLE 28. NITRATE-N CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A
SPRINKLER IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE
NEAR MUNDAY, TEXAS, ON AUGUST 8, 1972
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 29.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
Lateral di
0.0
2.8
1.4
1.8
1.4
1.7
1.3
2.5
12.7
5.9
1.4
1.8
1.6
1.5
1.9
2.3
25.4
2.2
1.5
1.1
1.3
1.5
2.3
2.4
38.1
2.9
1.2
1.6
2.4
0.9
2.9
1.0
50.
3.
1.
2.
2.
3.
3.
2.
stance, cm
8
7
7
2
7
5
0
4
63.5
2.2
1.5
3.8
4.1
3.0
1.8
NITRATE-N CONCENTRATION (PPM) AT SELECTED
SPRINKLER IRRIGATED PLOT (LOCATION 2) AT
NEAR MUNDAY, TEXAS, ON AUGUST 8, 1972
Lateral di
0.0
2.4
2.9
2.4
3.1
9.8
4.5
2.6
12.7
3.1
2.3
11.5
21.6
7.8
2.7
25.4
2.8
2.5
1.8
27.7
21.1
6.8
3.9
38.1
2.2
2.2
1.2
4.4
6.8
4.8
4.5
50.
1.
1.
1.
3.
4.
4.
3.
76.2
2.4
2.6
3.7
4.0
3.6
3.0
1.2
88
2
2
1
2
3
1
1
.9
.5
.2
.9
.8
.8
.8
.9
101.6
3.4
3.1
5.1
4.9
3.5
2.6
1.6
DEPTHS FROM A
THE FIELD SITE
stance, cm
8
2
2
9
2
6
2
9
63.5
7.4
2.4
1.9
4.9
12.3
6.8
4.2
76.2
3.1
2.5
1.2
2.4
11.7
9.4
3.4
88
4
1
2
1
3
6
6
.9
.8
.9
.1
.8
.5
.8
.0
101.6
3.9
2.3
2.6
1.4
1.8
7.5
7.9
282
-------
TABLE 30. NITRATE-N CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A
S?v~IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE NEAR
MUNDAY, TEXAS, ON AUGUST 8, 1972
Depth ,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 31.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
0.0
0.9
1.1
3.5
13.8
8.3
3.2
2.5
\2J
2.4
0.5
5.1
12.8
9.7
3.6
2.4
25.4
3.3
1.2
2.1
4.6
4.6
3.2
1.7
Lateral distance,
38.1
1.9
1.5
1.6
2.1
3.5
2.7
50.8
2.2
0.9
1.2
2.8
7.2
3.7
2.4
NITRATE-N CONCENTRATION (PPM) AT
FURROW- IRRIGATED PLOT (LOCATION
MUNDAY, TEXAS, ON AUGUST 8, 1972
63.
1.
1.
1.
4.
8.
cm
S
7
5
9
0
3
SELECTED
2) AT THE
Lateral distance,
0.0
2.0
2.0
1.4
1.9
3.1
5.6
5.7
12.7
1.4
1.2
1.5
1.9
2.5
6.8
6.1
25.4
1.6
1.7
2.1
2.6
1.9
7.7
8.4
38.1
1.7
1.5
1.6
2.7
3.8
8.9
8.5
50.8
2.3
3.2
5.0
8.9
7.8
7.8
7.1
63.
1.
3.
6.
12.
11.
8.
5.
cm
5
5
1
4
8
7
6
4
76
1
1
3
12
.?
.4
.4
.0
.3
DEPTHS
FIELD
76
1
2
5
10
11
7
4
.2
.6
.8
.3
.4
.7
.6
.0
88 Q
2.3
1.2
3.4
13.0
FROM
SITE
88.9
1.6
1.3
2.9
7.8
10.8
5.9
101.6
1.2
1.7
4.5
12.8
A
NEAR
101.6
1.4
1.2
1.9
6.2
10.2
3.9
2.2
283
-------
TABLE 32. NITRATE-N CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A SUB-
IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE NEAR MUNDAY,
TEXAS, ON AUGUST 8, 1972
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 33.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
Lateral distance, cm
0.0
3.2
6.3
4.5
1.9
2.0
1.8
2.3
12.7
2.1
4.5
6.8
2,3
2.0
2.5
2.6
NITRATE-N
IRRIGATED
TEXAS, ON
25.
2.
2.
1.
2.
2.
2.
2.
4
5
2
8
2
5
9
6
38.1
2.8
1.9
1.0
1.6
2.1
3.8
3.4
CONCENTRATION
PLOT (LOCATION
AUGUST 8, 1972
50.8
2.1
1.7
0.5
1.4
1.7
3.4
3.0
63.5
1.8
1.4
0.3
0.5
1.1
1.2
1.6
(PPM) AT SELECTED
2) AT THE FIELD
76.2
1.6
1.3
1.5
1.1
0.9
1.3
1.2
88
1
1
1
1
1
1
1
.9
.4
.4
.1
.5
.9
.0
.1
101.6
0.8
1.8
0.9
1.6
1.4
1.1
1.2
DEPTHS FROM A SUB-
SITE NEAR MUNDAY,
Lateral distance, cm
0.0
1.3
1.3
1.5
0.8
1.6
1.8
1.5
12.7
1.5
1.7
1.7
1.5
1.4
2.0
1.4
25.
1.
1.
1.
1.
1.
1.
1.
4
9
2
8
5
6
8
7
38.1
1.4
1.3
1.5
1.3
1.3
2.0
1.7
50.8
1.6
1.7
1.5
1.8
1.9
2.7
2.0
63.5
1.6
1.4
1.8
1.5
1.3
2.2
2.1
76.2
2.3
1.7
1.7
1.5
1.7
1.5
1.4
88
1
2
1
1
1
1
1
.9
.3
.2
.6
.6
.1
.4
.4
101.6
1.6
1.6
1.5
1.3
0.8
1.5
1.2
284
-------
TABLE 34. BROMIDE CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A SPRIN-
KLER-IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE NEAR MUNDAY,
TEXAS, ON AUGUST 8, 1972
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 35.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
0.0
2.4
0.5
1.0
0.0
0.0
0.2
0.0
12.7
1.1
0.8
8.8
0.1
0.0
0.0
0.0
25.
2.
0.
7.
0.
0.
0.
0.
4
8
1
1
0
0
0
0
Lateral
38.1
1.2
0.0
0.0
0.0
0.2
0.0
0.2
distance, cm
50.8
1.2
0.2
0.2
0.0
0.0
0.0
0.0
63.5
1.5
0.0
12.2
0.2
0.0
0.0
0.1
BROMIDE CONCENTRATION (PPM) AT SELECTED
KLER-IRRIGATED PLOT (LOCATION 2) AT THE
TEXAS, ON AUGUST 8, 1972
0.0
0.2
0.0
0.0
0.7
2.5
1.0
0.0
12.7
0.7
0.0
2.7
6.6
1.3
0.2
25.
0.
0.
0.
9.
7.
0.
0.
4
1
0
0
1
5
3
2
Lateral
38.1
0.3
0.0
0.4
0.2
1.2
0.2
0.1
76.2
1.7
0.0
9.9
0.0
0.0
0.0
0.2
88
1.
0.
1.
0.
0.
0.
0.
Q
1
0
1
0
0
0
0
DEPTHS FROM A
FIELD SITE NEAR
101.6
0.8
0.0
0.0
0.6
0.0
0.0
0.0
SPRIN-
MUNDAY ,
distance, cm
50.8
0.5
0.0
0.0
0.0
0.2
0.4
0.1
63.5
3.5
0.0
0.0
0.1
1.8
15.9
0.3
76.2
0.8
0.0
0.0
0.0
3.1
2.2
0.7
88.
3.
0.
0.
0.
0.
6.
4.
9
6
0
0
0
0
1
6
101.6
3.1
0.0
0.0
0.0
0.0
4.8
6.1
285
-------
TABLE 36. BROMIDE CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A FURROW-
IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE NEAR MUNDAY,
TEXAS, ON AUGUST 8, 1972
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 37.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
0.0 1
0.2
0.0
0.2
2.1
0.0
0.0
0.0
2.7 25.4
0.0 0.1
0.0 0.0
0.0 0.0
0.4 0.0
0.2 0.1
0.0 0.0
0.0 0.0
Lateral
38.1
0.0
0.0
0.1
1.3
0.0
0.0
BROMIDE CONCENTRATION (PPM)
IRRIGATED PLOT (LOCATION 2)
TEXAS, ON AUGUST 8, 1972
0.0 12.7 25.4
7.6
0.5
0.6
0.0
2.0
2.5
2.8
0.9 1.0
0.4 0.1
0.1 0.1
0.2 0.1
0.8 0.7
2.1 2.8
2.2 3.2
Lateral
38.1
0.6
0.1
0.5
0.0
0.2
2.2
3.0
distance, cm
50.8 63.5
0.0 0.1
0.0 0.0
0.0 0.0
^
0.9 0.0
1.7 3.7
0.3
0.6
AT SELECTED
AT THE FIELD
distance, cm
50.8 63.5
1.3 0.6
0.1 0.9
1.2 1.3
0.0 0.7
0.3 2.8
0.3 0.2
1.2 0.3
76.2
0.9
0.2
0.1
0.1
10.6
DEPTHS
SITE
76.2
1.0
0.3
0-4
0.9
0.8
0.0
0.0
88.9
0.8
0.1
0.2
1.3
11.5
101.6
0.1
0.3
2.9
11.5
FROM A FURROW-
NEAR MUNDAY,
88.9
0.7
0.6
0.1
0.1
0.2
0.0
101.6
0.6
0.4
0.4
0.5
0.2
0.0
0.0
286
-------
TABLE 38. BROMIDE CONCENTRATION (PPM) AT SELECTED DEPTHS FROM A SUB-
IRRIGATED PLOT (LOCATION 1) AT THE FIELD SITE NEAR MUNDAY,
TEXAS, ON AUGUST 8, 1972
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2.1
TABLE 39.
Depth,
m
0.3
0.6
0.9
1.2
1.5
1.8
2,1
0.0
7.8
31.4
11.2
0.4
0.1
0.0
0.0
2J
3.8
4.0
7.6
1.2
0.0
0.0
0.0
2b
2
1
1
0
0
0
0
.4
.0
.9
.0
.2
.0
.1
.0
Latera
38.1
3.9
1.3
0.3
0.0
0.0
0.0
0.0
BROMIDE CONCENTRATION (PPM)
IRRIGATED PLOT (LOCATION 2)
TEXAS, ON AUGUST 8, 1972
0.0
0.8
0.0
0.0
0.0
0.0
0.0
0.0
12.7
0.7
0.0
0.0
0.0
0.0
0.0
0.0
25
2
1
0
0
0
0
0
.4
.0
.8
.0
.0
.0
.0
.0
Lateral
38.1
1.3
1.8
0.1
0.0
0.0
0.0
0.5
distance, cm
50.8
2.9
0.0
0.8
0.0
0.0
0.0
0.0
63.5
1.3
0.8
0.9
1.3
0.1
0.0
0.0
AT SELECTED
AT THE FIELD
76 ?
1.1
0.0
0.1
0.0
0.0
0.0
0.0
DEPTHS
SITE
88
0.
0.
0.
0.
0.
0.
0.
FROM
NEAR
Q
9
3
2
0
0
0
0
101.6
0.4
0.1
0.2
0.0
0.0
0.0
0.0
A SUB-
MUNDAY,
distance, cm
50.8
0.5
1.0
0.1
0.0
0.0
0.0
0.0
63.5
0.5
0.4
0.3
0.0
0.0
0.0
0.4
76.2
3.0
0.1
0.0
0.0
0.0
0.0
0.0
88.
2.
0.
0.
0.
0.
0.
0.
9
2
0
0
0
0
0
0
101.6
1.3
0.0
0.0
0.0
0.0
0.0
0.7
287
-------
TABLE 40. NITROGEN CONCENTRATIONS (PPM) OF SOIL-WATER EXTRACTS FROM POROUS BULB SAMPLES. SUB-IRRIGATED
PLOT, 1972
Plane*
A
Date
July 28
Aug. 14
Aug. 28
Sept. 6
Sept. 14
Sept. 21
Oct. 2
Depth,
m
0.15
0.30
0.46
0.61
0.91
1.22
1.52
0.15
0.30
0.46
0.61
0.91
1.22
0.15
0.30
0.46
0.61
0.15
0.30
0.46
0.61
0.91
1.22
1.52
0.15
0.30
0.46
0.61
1.22
0.15
0.30
0.46
0.61
0.91
1.22
0.15
0.30
0.46
0.61
1.22
NO~-N
24
6
17
7
8
9
10
810
180
170
14
9
11
267
86
240
97
20
10
27
27
13
12
73
4
11
170
16
7
27
10
1
2
NH+-N
6
0
0
2
0
3
10
189
51
2
1
0
1
67
1
1
2
12
3
1
1
2
1
21
0
1
4
12
2
1
11
2
8
B
NOJ-N
23
42
23
13
21
6
5
16
160
99
15
33
6
27
170
110
6
7
82
67
24
20
38
8
18
51
46
26
52
18
31
23
18
33
19
4
18
11
NH+-N
8
1
0
0
38
6
35
7
1
2
1
26
2
1
4
2
1
1
2
4
7
4
8
1
1
1
2
0
1
1
1
2
10
5
1
1
2
3
C
NOg-N
nn
HP
92
15
37
57
25
9
130
32
78
26
19
27
40
6
4
71
81
30
9
19
73
37
12
17
52
65
15
13
40
70
NH4-N
m " .'"..--.."'•-."•1-1-
16
i
2
6
3
1
1
1
1
2
3
1
2
2
2
2
8
2
1
1
2
4
3
1
1
2
13
2
2
10
1
NOg-N
31
7
6
10
7
4
9
180
83
21
14
7
160
25
135
150
27
17
51
99
36
16
6
no
16
83
no
11
1
35
21
93
5
5
9
}
NH+-N
2
0
0
3
13
6
1
69
1
0
1
4
50
3
0
1
6
0
1
1
10
4
1
1
1
1
13
1
0
1
4
15
0
1
4
E
NOg-N I
12
7
6
6
16
5
9
7
16
8
12
12
33
12
22
26
1
2
10
6
18
1
3
4
4
8
105
1
2
1
8
2
2
3
6
-------
MAY 31
JUNE 12
JUNE 22
JULY 6
JULY 28
ro
CO
DEPTH,
m
0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
LAT.DIST.,
cm
51 102
Figure 180. Lateral and vertical distribution of nitrate-N ( ), fertilizer-N ( .) and
bromide (Illlllllttt) by date in soil sample extracts from Plot 6-1. (Sprinkler-irrigated
fertilized with N-enriched sodium nitrate)
-------
MAY 31
JUNE 12
JUNE 22
JULY 6
JULY 28
ro
10
o
LAT. DIST.,
DEPTH, cm
m
0 51 102
0-0.3 0%
0.3-0.6
0.6-0.9
0.9-1.2
1.2-1.5
Figure 181. Lateral and vertical distribution of nitrate-N (———), fertilizer-N ( )
and bromide (\\\X\\\\\V) by date in soil sample extracts from Plot 18-1. (Furrow-
1 5,
irrigated - fertilized with N-enriched sodium nitrate)
-------
MAY 31
JUNE 12
JUNE 22
JULY 6
JULY 28
DEPTH,
m
0-0.3
0.3-0.6
LAT. DIST.,
cm
51 102
0.6-0.9
Figure 182. Lateral and vertical distribution of nitrate-N ( —) , fertilizer-N (-
('/////////) by date in soil sample extracts from Plot 32-1. (Subirrigated
15N-enriched sodium nitrate)
— ) and bromide
fertilized with
-------
Data from these same 15N plots in 1974 show that approximately two weeks
after the application of the banded fertilizer material on June 6 that in the
top 0.3 m of soil the sprinkler plot contained 53 kg of nitrate-N/ha, the
furrow plot 64.4 and the subirrigated plots 81.2, showing again that the
subirrigated plots kept more nitrate-N in the upper part of the profile
longer than did the furrow system which kept it there longer than did the
sprinkler system.
The data' in Table 25 show that in the process of accounting for the
amount of nitrogen applied as fertilizer in 1973 and 1974 using 15N as a
tracer that of this nitrogen, 85.8 kg/ha was found in the organic form under
the sprinkler plots, 31.6 kg/ha in the organic form under the furrow plots,
and 19.4 kg/ha under the subirrigated plots. This indicates, since the crop
residue was all applied to the soil and the amounts of fertilizer nitrogen
actually removed by the plant material in 1973 were not that greatly differ-
ent between the systems, that this organic residue must have been broken down
and the nitrogen released into the soil from the organic fraction to a much
greater extent in the subirrigated than in the furrow or in the sprinkler
plots.
Water potential data at the 0.3-m level in the soil are given in
Figures 183, 184, and 185 for the plots that were intensively sampled using
both bromide and nitrate, for the subirrigated plots used in the second crop
in 1972, and for the 15N plots for 1974. Figure 185 for the 15N plots in
1974 shows that the subirrigated plots at the 0.3-m depth had a potential of
-10 cb or more throughout the growing season. It can be seen that the poten-
tial was lower in the furrow- and sprinkler-irrigated plots than in the
subirrigated plots during the growing season at this depth. Much the same
trend can be seen for the second crop in 1972 (Figure 184) with the subirri-
gated and furrow plots being somewhat closer together in the amount of time
that a potential >-10 cb existed at the 0.3-m depth in the soil. In contrast
to this, the data in Figure 183 show that the subirrigated and furrow-
irrigated plots had water potentials >-10 cb above field capacity more of the
time than did the sprinkler plots. Bremner and Shaw (2) have pointed out
that losses to dem'trification may occur when the soil moisture is greater
than 60% of the water-holding capacity. The subirrigation systems in this
study had 100% of the water-holding capacity much of the growing season.
This combination of factors, i.e., holding the nitrate-N up in the pro-
file in conjunction with water potentials at or near field capacity for
substantial portions of the growing season apparently resulted in a process
of dem'trification which then resulted in the loss of the nitrate-N from the
profile into the atmosphere. The necessity for keeping the nitrate-N in the
upper portion of the profile is of course shown by the distribution patterns
of nitrate under sprinkler and furrow systems and the accountability of the
amount of nitrogen applied as fertilizer in 1973 and 1974 in the 15N tracer
plots. In this particular study, it was found that it was possible to
account for 92.6%, 86.1%, and 50.5% of the fertilizer nitrogen applied to
the sprinkler, furrow, and subirrigation systems, respectively. Thus,
practically all of the nitrogen could be accounted for over a two-year period
that was applied as fertilizer for the sprinkler plots. It is possible that
part of the nitrogen not accounted for did leave the soil by a process of
292
-------
ro
l£>
oo
-60 r
-48-
.a
o
£
co
O
I—
-------
ro
-Q
O
£
oo
O
-35
-30
„ -25
-20
-15
c± -10
-5
0
+5
LU
O
o
00
Figure 184.
O- SPRINKLER
O - FURROW
D - SUBIRRIGATION
14
AUGUST
24
13
SEPTEMBER
23
13
OCTOBER
Water potential measured at 0.3 m during the growing season of 1972 for plots
fertilized with sodium nitrate and sodium bromide, planted to sweet corn and
irrigated by three methods.
-------
-50-
O- SPRINKLER
Q- FURROW
D - SUBIRRIGATION
_Q
U
oo
O
ro
vo
01
O
D_
-------
denitrification, some of it may also have been tied up in the root system of
the crop and was not included in the soil sample analyses. The same state-
ments could be made for the 14% that was not recovered for the furrow plots,
and possibly in this situation a somewhat greater amount of fertilizer might
have been lost due to denitrification in that, as shown in the tables con-
taining the data for nitrate-N distribution in the profile, nitrate-N was
held up in the profile longer in the furrow plots than in the sprinkler
plots, thus increasing the potential for denitrification. The recovery of
only 50% of the fertilizer nitrogen from the subirrigated plots and the data
showing that the nitrogen was not in the plant material nor in the soil pro-
file is strongly indicative of loss through denitrification. Certainly the
conditions necessary for denitrification were present; namely, nitrate reten-
tion in the upper portions of the soil profile, low water potentials and a
readily available energy source for anaerobic organisms, which was apparently
used.
In conclusion, the quality of irrigation return flow to underground
water was much superior under subirrigation compared to the other two irri-
gation systems from the standpoint of nitrate-N from applied fertilizer. The
reason for this apparently was the retention of nitrate-N that was banded
into the soil above the subirrigation lateral, the maintenance of water
potentials at or above field capacity for substantial time periods in a zone
with the nitrate and in a zone where an energy source was available for the
anaerobic organisms to convert the nitrate to a gaseous nitrogen form where
it was lost into the atmosphere. Thus, not only can we, through use of this
system, have a good quality irrigation return flow, from the standpoint of
fertilizer nitrate, by reducing its movement; but it is, in fact, removed
from the soil environment altogether if it is not used or incorporated into
plant tissue. Whether removed from the soil by the process of denitrifica-
tion or incorporated in plant tissue, it is not subject to leaching by rain-
fall during winter months and thus the movement of the nitrate under this
system into underground water would certainly be minimized.
Water Requirements of Sweet Corn Irrigated With Furrow, Sprinkler, Manual
Subirrigation and Automatic Subirrigation
Investigation of the much-discussed concept of using irrigation water
more efficiently to decrease the amount of water available for irrigation
return flow and amount of salt applied was one of the objectives of this
project. The facilities of this project afforded the opportunity to compare
sprinkler irrigation, furrow irrigation, subirrigation, and automatic subir-
rigation as to their efficiency of water application. Descriptions of these
systems are presented in the Methods and Materials Section.
The generalized water budget model used in comparison was:
AW = M + Ir - N - F - (E+T) [Hillel (8)] [19]
(Definitions on following page)
296
-------
Parameter
Method of Measurement
AW = Change in water content
M = Precipitation
Ir = Irrigation water
N = Runoff )
F = Deep percolation )
E+T = Evaporation + Transpiration
or Evapotranspiration (ET)
Calibrated neutron probe
Rain gauge
Flow meter
None during the growing
season of the crop
During the growing season, there was no runoff from the plots. Also,
the location of peak concentrations of a bromide tracer in the root zone
remained nearly constant during the growing season. This fact indicates that
there was negligible deep percolation during this period. Since there was no
runoff or deep percolation from the plots, Equation 19 became the following:
ET = M +
- AW
[20]
Criteria for applying water through the various irrigation systems are
shown in Table 41. Water was applied when the potential at 30 cm decreased
to -40 cb. Due to the porosity of the loamy fine sand soils, it was not
possible to apply less than 7.6 cm of irrigation water per application with
the furrow system. In the sprinkler-irrigated and manually-subirrigated
plots, it was possible to apply a percentage of potential ET at each appli-
cation varying according to stage of growth. Water was applied as needed to
the automated subirrigated plots when the potential decreased to -40 cb until
the potential increased above -40 cb. Eight replications of yield data were
obtained from each treatment.
TABLE 41. CRITERIA FOR APPLYING IRRIGATION THROUGH THE VARIOUS SYSTEMS IN A
COMPARISON OF THE WATER EFFICIENCY OF IRRIGATION SYSTEMS IN KNOX
COUNTY, TEXAS, 1973
System
Furrow
Sprinkler
Indicator
Tensiometer
Tens iometer
Read i ng ,
cb
40
40
Amount of
water applied
7.62 cm
Percentage of
potential ET*
Subirrigation
Automatic
subirrigation
Tensiometer
Switching
tensiometer
40
40
Percentage of
potential ET*
Adequate to in-
crease poten-
tial above
-40 cb
* Potential ET as proposed by Jensen, et al. (10J,
297
-------
The water applied and yield of the sweet corn in the study are shown in
Table 42. On the surface it would appear that possible breakthroughs in the
amount of water required by sweet corn might be forthcoming. Essentially,
the same yield of sweet corn was obtained when 13.0 cm of water were applied
using automatic subirrigation, 20.2 cm using manual subirrigation, 25.1 cm
using sprinkler irrigation, and 38.1 cm using furrow irrigation. Similar
variation existed among irrigation systems, i.e., some of the subirrigated
plots used over 25 cm and some of the sprinkled plots used as low as 20 cm
(Table 42). The treatments discussed in this section received the same
fertilizer treatments of 45.5 kg of nitrogen in the form of Uran applied
through the irrigation water.
Rainfall and irrigation distributions during the studies are also shown
in Table 42. In the furrow plot, five 7.62-cm irrigations were applied.
Five irrigations varying anywhere from 4.19 to 6.86 cm were applied to the
sprinkler-irrigated plot. Three applications of water which varied from
5.33 to 8.00 cm were applied to the manual subirrigation plot. To the plot
with automatic subirrigation, 25 applications varying from 0.15 to
0.86 cm/application were applied. In general, the amounts applied through
the automated subirrigation system were in the range of the amounts received
in showers from rainfall.
Major differences occurred in the soil-water content among treatments in
the soil profile (Figures 186 and 187). As shown in Figures 10, 11, and 12,
the soil profile is quite variable, but among the systems there were some
characteristics in common. In general, with furrow irrigation systems, water
was applied in excess of potential ET due to the characteristics of the
system such that at the end of the season there was an increase in soil-water
content compared to the beginning of the season. In the sprinkler-irrigated
treatment, a portion of the soil profile had a water content increase, and a
portion of it had a decrease between the beginning and end of the season.
Below 3 m, drainage occurred from the winter rains prior to the growing
season. In the case of subirrigation, there was a slight decrease in water
content in the root zone and a decrease below the root zone indicating
drainage during the growing season. Treatments with automatic subirrigation
had a major decrease in the soil-water content of the soil profile above
1.8 m during the growing season. Due to major differences in soil-water
content changes during the growing season among the systems, the variation
in the amount of water used by sweet corn irrigated by the different systems
(Figure 188) was much less than the variation in the amounts of water applied
(Table 42). Corn irrigated with the furrow system still required the most
water--36.1 cm, while the corn irrigated with the sprinkler and subirrigation
systems required 34.6 and 34.0 cm, respectively. The corn irrigated with the
automated subirrigation system required 30 cm of water or 6.1 cm less than
the furrow irrigation system. The accumulative ET based on changes in water
content and water applied parallels the potential ET line in the latter part
of the growing season, indicating that the crop at this time was using water
approximately equal to the potential ET.
Leaf area measurements of the corn growing on the various systems were
made using a relationship between plant diameter 2.54 cm above the ground
and the leaf area for each different system. In Figure 189, it can be seen
298
-------
TABLE 42. RAINFALL RECEIVED AND IRRIGATION WATER APPLIED TO SELECTED
PLOTS IN THE VARIOUS IRRIGATION SYSTEMS IN KNOX COUNTY,
TEXAS, IN 1973
Date
May 13
14
21
22
23
June 1
2
5
7
8
n
13
14
15
16
17
18
19
20
21
22
23
25
26
27
29
30
v* w
July 2
3
tj
4
*T
8
q
y
n
12
I L.
Totals
Yield,
ears/ha
Rainfall ,
cm
0.25
0.43
0.25
0.89
0.13
2.84
0.48
0.38
0.18
0.36
0.33
0.56
1.27
8.35
Irrigation water applied,
cm
Automated
Sprinkler Furrow Subirrigation subirrigation
6.86
0.43
7.62 0.20
0.28
7.24
0.43
0.28
0.15
0.71
,7.62 0.58
5.72
0.58
5.33 0.71
0.43
0.43
7.62 0.15
0.86
4.19 0.46
0.71
0.58
7.62 8.00 0.71
4.32 0.71
0.43
0.71
0.71
0.71
4.45 7.62
0.58
0.61
24.27 38.10 20.57 13.14
40,138 38,902 43,225 39,520*
* Yields are not significantly different at the 5% level of probability.
299
-------
OJ
o
o
0.6
1.2
1.8
2.4
E
rv
t 3.6
LU
4.9
6.1
7.3
8.51-
Figure 186.
10
20
SOIL-WATER CONTENT, volume
30 10
20
//// AREA:
CLEAR AREA:
DECREASE IN SOIL-
WATER CONTENT
INCREASE IN SOIL-
WATER CONTENT
FURROW
T
SPRINKLER
Changes in soil-water content with depth between the beginning and end
of the growing season in the furrow- and sprinkler-irrigated plots in
the 1973 irrigation systems study, Knox County, Texas.
-------
U>
CD
D-
LU
0.6 -
1.2-
1.8
2.4
3.6
4.9
6.1
7.3
10
20
SOIL-WATER CONTENT, volume
30 10
20
30
CLEAR AREA:
//// AREA:
51-
Figure 187.
DECREASE IN SOIL
WATER CONTENT
INCREASE IN SOIL
WATER CONTENT
SUBIRRI GATION
AUTOMATED
SUBIRRIGATION
Changes in soil-water content with depth between the beginning and end of
the growing season in the manually- and automatically-subirrigated plots
in the 1973 irrigation systems study, Knox County, Texas.
-------
50
40
30
o
i—i
H-
-------
FULL TASSEL
SPRINKLER
X
LU
<
LU
o:
u_
-------
that there was little difference in the LAI of corn grown over the furrow
irrigation and the manual subirrigation systems. The corn grown with the
automatic subirrigation and sprinkler irrigation systems was slightly greater
in leaf area.
Plant evaporation in relation to potential evaporation as influenced by
leaf area was compared to a relationship derived by Ritchie and Burnett (21)
(Figure 190). It can be seen that the points for subirrigation fall slightly
below the line, whereas most of the other points are above the line. This
indicates that the corn grown on the different irrigation systems followed
this particular relationship. This would also indicate that, although there
were different amounts of water applied to the crop, no major breakthroughs
relative to water requirements of crops were obtained -- but rather major
increases in water application efficiency due to differences in irrigation
systems.
In conclusion, when one considers the changes in water content along
with irrigation water applications, there was little difference in ET by
sweet corn grown over the different systems. Therefore, what on the surface
may appear to be a major breakthrough in water requirements of crops can be
explained by decreases in soil-water content. It appears from these data
that a sweet corn crop required approximately the same amount of water for a
given yield regardless of the irrigation system. However, automation of
irrigation systems does afford the possibility of making more efficient use
of water stored in soil profiles. This factor should not be discounted in
those areas where supplemental irrigation rather than full irrigation is
used. A zone of lower moisture content can be developed to store rainfall
yet the crop can obtain adequate moisture and not become stressed. It is
realized that sophisticated irrigation systems do not exist except on high
value crops. However, it is believed that automation of furrow and sprinkler
systems deserves further investigation as a means of increasing application
efficiency. Irrigation return flow can be reduced in those areas that do not
require a leaching requirement by either automated system or by use of a
measure of ET as a basis of irrigation. However, in most irrigated areas,
leaching requirements would need to be included and such a requirement could
be built into automated systems or included along with the ET potential.
It should be pointed out that, in these treatments, no applied water or
nutrients moved below the root zone during the growing season from any of the
treatments. Although more water was applied with the manually-operated
system, the use of potential ET as a basis for scheduling applications could
also be used to minimize water available for irrigation return flow. Such a
scheduling technique could also include the leaching requirement.
OBJECTIVE 4 - ECONOMICS OF INSTALLATION, OPERATION, AND MAINTENANCE OF
SUBIRRIGATION SYSTEMS AND OF EACH FERTILIZATION PRACTICE
Economic Implications of Sprinkler^Irrigation, Furrow Irrigation, and
Subirrigation Systems Fertilized With Various Rates of Nitrogen
Based on the results obtained from 1971-1973, some general economic
implications emerge. Since estimated costs and returns for the alternative
304
-------
CO
o
en
Ep
Eo
l.or
0.8
0.6
0.4
0.
0.0
RITCHIE AND
BURNETT (21)
IRRIGATION SYSTEM
o-
n -
A-
O -
FURROW
SPRINKLER
SUBIRRIGATION
AUTOMATIC
SUBIRRIGATION
0.4 0.8 1.2 1.6 2.0
LEAF AREA INDEX
2.4
2.8
3.2
Figure 190. Plant evaporation (Ep) of sweet corn produced with different irrigation
systems in relation to potential evaporation (Eo) as influenced by leaf
area index.
-------
irrigation distribution systems are closely related to crop yield, the per
hectare yield for each year (1971-1973)is presented for reference in
Table 43, by research plot. Per hectare yields were based on ear weight in
each plot. Water and fertilizer applied for each situation shown in Table 43
are indicated elsewhere in the general report.
To maintain consistency, the same price and cost assumptions were
applied to each year to estimate per hectare net returns. These input and
product prices as well as other input requirements and associated costs were
taken from several references (6,12,13,14,22). Basically, costs and returns
were calculated using the following data:
Price or
cost,
Item Unit dollars
Returns
Sweet corn quintal $ 15.90
Costs
General production hectare 118.90
Labor hour 2.00
Harvesting quintal 7.16
Nitrogen kilogram 0.26
Pumping ha-cm 1.13
In addition, an annual fixed cost, based on investment, was included
for each irrigation distribution system ($6.72 - furrow, $19.96 - sprinkler,
$300.52 - manual subirrigation, and $374.45 - automated subirrigation). The
per hectare net returns, by plot and year as shown in Table 43, were esti-
mated based on this information.
With a reduction in the investment required for a subirrigation system
($2,470 per hectare used in this study), annual fixed costs would decline and
present a more favorable net return picture. Likewise, a higher sweet corn
price would result in higher net returns. Therefore, it is important to be
aware of the limitations of the assumed prices and costs used for this
analysis.
The data in Table 43 were aggregated by year and nitrogen application
rate for each of the distribution systems. In those cases where the nitro-
gen rate was changed appreciably, the research plot was not included in the
aggregation. The research plots included in each aggregation are as follows:
306
-------
TABLE 43. PER HECTARE YIELD AND EXPECTED NET RETURNS FOR SWEET
CORN BY RESEARCH PLOT: 1971-73.
Plot
1
2
3
4
5
6
7
8
9
10
n
12
13
14
15
16
17
18
19
20
21
t_ i
22
£» £—
23
24
d,™
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
-----
1971
15.8
14.7
22.4
34.2
39.1
17.5
26.8
41.1
19.7
30.9
10.0
36.0
52.5
9.1
39.2
24.0
43.0
16.4
39.1
25.1
15.1
9.4
20.2
19.5
39.8
19.9
S
20.9
32.9
43.0
33.7
40.9
30.5
58.0
40.3
41.4
45.0
22.3
40.9
42.4
.— — •
Yield
1972
quintal -
15.0
21.7
26.4
23.1
19.3
13.1
19.6
25.0
10.8
35.3
13.4
43.9
42.6
11.5
33.3
81.2
53.2
17.6
27-4
71.5
40.2
11.1
46.9
32.8
43.1
24.0
17.2
37.3
41.3
45.6
63.8
20.5
23.5
25.8
47.6
28.6
10.0
19.7
42.1
—
Net returns
1973
34.8
63.1
75.0
80.0
69.2
62.8
69.2
83.3
77.1
79.0
35.8
75.0
75.0
17.9
52.8
66.4
71.7
70.7
61.0
50.8
66.4
16.0
65.4
53.3
63.5
70.2
18.9
54.2
82.8
71.7
68.8
73.1
67.9
71.7
58.6
67.3
24.8
63.5
41.2
., —
1971
-54.3
-81.5
-27.2
29.6
106.2
0
-17.3
113.6
-96.3
24.7
-108.7
86.5
232.2
-116.1
150.7
-7-4
170.4
-42.0
113.6
-4.9
-108.7
-93.9
-29.6
-34.6
140.8
-32.1
-289.0
-190.2
-128.4
-214.9
-148.2
-210.0
12.4
-165.5
-168.0
-138.3
-298.9
-160.6
-145.7
_ • —
1972
- dollar -
-54.3
-4.9
0
-29.6
-59.3
-71.6
-24.7
-2.5
-130.9
81.5
-69.2
145.7
135.9
-69.2
106.2
471.8
239.6
-9.9
46.9
390.3
128.4
79.0
190.2
71.6
158.1
-2.5
-306.3
-140.8
-145.7
-111.2
37.1
-281.6
-269.2
-271.7
-98.8
-261.8
-373.0
-335.9
-145.7
- — — •—
1973
108.7
321.1
415.0
449.5
360.6
303.8
373.0
476.7
424.8
439.7
113.6
407.6
405.1
29.6
242.1
340.9
392.7
375.4
311.2
247.0
340.9
-39.5
340.9
237.1
321 .1
395.2
-293.9
-17.3
202.5
113.6
86.5
121.0
88.9
108.7
0
69.2
-251.9
39.5
-148.2
Continued
307
-------
TABLE 43.
(Continued)
Plot
1971
Yield
1972
1973
1971
Net returns
1972
1973
40
41
42
43
44
45
46
System
Sprinkler
— v^u i nua i
24.8
27.0
19.0
33.0
34.2
18.4
36.2
50.8
62.0
30.5
52.8
69.8
29.6
43.1
Nitrogen
rate,
kg/ha
0
22.4 - 67.2
112.0
uui iar —
-343.3
-321.1
-353.2
-266.8
-256.9
-358.2
-24.7
Research plots
1, 11
2, 7
3-5, 8-10, 12,
-123.5
-17.3
-266.8
-108.7
-49.4
-269.2
49.4
13
Furrow
Manual Subirrigation
Automated Subirrigation
Trickle
0
22.4 - 67.2
112.0
0
22.4 - 67.2
112.0
0
112.0
112.0
14, 22
15, 19
16, 17, 20, 21, 23-26
27, 37
28, 33
29-31, 34-36, 38, 39
42, 45
40., 41, 43, 44
46
The aggregated results for yield per hectare and expected net returns
are presented in Table 44. For each nitrogen application rate and distri-
bution system, the 1973 yield per hectare was appreciably larger than 1971
and/or 1972. This increased yield is generally reflected in the correspond-
ing expected net returns. Therefore, it is appropriate to first consider
the 1973 results.
Yields in 1973 associated with the manually-operated Subirrigation
system were a) less than that indicated using sprinkler irrigation and
b) about the same or a little larger than yields obtained with furrow irri-
gation, for each fertilization rate. Net returns per hectare, by fertili-
zation rate, were significantly lower using the Subirrigation systems
compared to sprinkler or furrow irrigation. Over the three-year period
308
-------
CO
o
ID
TABLE 44. PER HECTARE YIELD AND EXPECTED NET RETURNS FOR SWEET CORN FOR ALTERNATIVE FERTILIZER
RATES AND METHODS OF APPLYING IRRIGATION WATER, 1971-1973
Yield
System
Sprinkler
Furrow
Manual
subirrigation
Automated
subirrigation
Nitrogen
1971
1972
1973
0
22.4 -
112
0
22.4 -
112
0
22.4 -
112
0
112
67.2
.0
67.2
.0
67.2
.0
.0
12.9
20.7
34.5
9.3
39.2
25.9
21.6
45.5
41.0
i|u i ii uu r
14.2 35.4
20.6 66.2
28.3 76.6
11.3
30.4
49.2
13.7
30.5
39.3
18.7
29.7
17.0
56.9
63.5
21.8
61.0
65.7
30.0
58.8
Avq.
20.8
35.6
46.5
12.5
42.1
46.1
19.0
45.7
48.7
24.4
44.2
1971
Net returns
1972
1973
Avg.
-81
-49
59
-103
130
9
-293
-88
-158
.51
.40
.28
.74
.91
.88
.93
.92
.08
UU 1 1 U 1
-61.75 111.15
-14.82 345.80
17.29 422.37
4.94
76.57
205.01
-340.86
-205.01
-165.49
-355.68
-296.40
-4.94
276.64
326.04
-271.70
37.05
59.28
-269.23
-49.40
-10.70
93.86
166.31
-34.58
161.37
180.31
-302.16
-85.63
-88.10
-312.46
-172.90
Trickle 112.0 36.2 43.1 39.6 -24.70 49.40 12.35
-------
(1971-1973), net returns were positive for subirrigation in 1973 only; i.e.,
$37 for 22.4 to 67.2 kg of nitrogen and $59 for 112 kg of nitrogen.
The three years' data were averaged to determine expected yields and net
returns for the alternative situations. The first year (1971) was one of
testing and gaining experience with the equipment while 1973 was a year of
exceptionally good growing conditions. Considering the manually-operated
subirrigation system, associated yields at each fertilization level were
larger than sprinkler or furrow irrigation with the single exception of no
nitrogen fertilizer and sprinkler irrigation. With 112.0 kg of nitrogen
fertilizer, average yield with the subirrigation system was 48.7 quintal
compared to about 46.4 quintal with sprinkler and furrow irrigation.
Even with the increased yields, the larger fixed costs of subirrigation
due to the $2,470/ha initial investment more than offset any yield advantage.
Net returns were negative for all situations using subirrigation (-$302,
-$86, and -$88 for 0, 22.4 to 67.2, and 112 kg of nitrogen, respectively).
Net returns for 112 kg of nitrogen were about $173/ha for the sprinkler and
furrow irrigation systems or over $240 greater than with subirrigation.
The net return estimates indicate that the assumed investment in subir-
rigation systems of $2,470/ha cannot be economically justified. However,
subirrigation technology could quickly reduce investment costs as well as
further increase yields, relative to traditional irrigation systems. There-
fore, the analysis was extended to a) establish the investment in a subirri-
dation system which would produce the same net returns per hectare as
sprinkler and furrow irrigation given average yields of Table 44, and b)
establish the yield required to produce the same net returns per hectare as
sprinkler and furrow irrigation given the $2,470/ha manual subirrigation
investment and $2,780/ha automated subirrigation investment.
Break-even investment for a subirrigation system is shown in Table 45.
For example, with 112 kg of nitrogen applied, an investment of $528/ha in a
subirrigation system would result in the same net returns as a sprinkler
irrigation system. This indicates that if the investment was lower than
$528/ha, the subirrigation system would be more profitable than a sprinkler
system.
For 112 kg of nitrogen applied to sweet corn, the break-even investment
for a manual subirrigation system is $528 when compared to a sprinkler system
and $407 compared to a furrow system. With nitrogen reduced to 22.4 to
67.2 kg/ha, a much larger break-even investment evolves; i.e., $1,126
analyzed against furrow.
Break-even investment for the automated subirrigation system, with
112 kg of nitrogen applied, indicates a smaller value than for the manual
system which means it is at a comparative disadvantage. Comparing an auto-
mated system to a sprinkler system, the investment in the automated system
must be held down to about $432/ha for production to be as profitable as
with a sprinkler system. The investment could be only $311 to be comparable
to furrow irrigation net returns.
310
-------
TABLE 45. ESTIMATED PER HECTARE SUBIRRIGATION INVESTMENT WHERE NET RETURNS
WOULD BE EQUAL TO NET RETURNS FOR SPRINKLER AND FURROW IRRIGATION
BASED ON 1971-1973 DATA*
Nitrogen
applied
l/n
^y
0
22.4 - 67.2
112.0
Manual subirrigation
Sprinkler Furrow
133 336
1,126 580
528 407
Automated
Sprinkler
1,971
t
432
subirrigation
Furrow
2,174
t
311
'Based on average yields and operation costs, by system, for 1971-1973.
tlnformation not available.
This suggests the manual subirrigation system is closer than the auto-
mated system to being economically feasible. These data indicate that the
investment in a subirrigation system will have to decline to about $500 to
S750/ha before they are economically competitive with traditional systems.
Viewing break-even yield, Table 46 shows the estimated yield under sub-
irrigation where net returns with subirrigation would be equal to sprinkler
and furrow irrigation, given an investment of $2,470 and $2,780/ha for a
manual and automated system, respectively. Considering only situations with
nitrogen fertilization, the break-even yields for both subirrigation systems
compared to sprinkler and furrow irrigation are relatively close. For 112 kg
of nitrogen, the break-even yields are 63.8 to 66.1 quintal/ha across all
systems. This represents a one-third increase in 1971-1973 average yield for
the manual subirrigation system and a 50% yield increase for the automated
subirrigation system.
Among the many limitations of this economic analysis are a) no consid-
eration of efficiency of water use which would be extremely important in
areas with an exhaustible water supply, b) constantly shifting prices for
inputs and products, c) only one crop being included, and d) no marketing
problems were considered, etc.
Effect of Irrigation Systems, Irrigation Criteria, and Fertilizer Source on
Water-Use and Fertilizer Efficiency~
The section on economic evaluation was concerned primarily with systems
cost and nitrogen cost and did not deal specifically with the effects of
irrigation systems, irrigation criteria, and sources of fertilizer on water-
use and fertilizer efficiency. Due to the high interest concerning the
efficiency of irrigation systems and sources of fertilizer, it was decided
that a discussion of these parameters in more detail would be advisable.
The discussion of the influence of the criteria for irrigation water, irri-
gation system, and fertilizer source on the various yield parameters
follows.
311
-------
TABLE 46. ESTIMATED PER HECTARE SUBIRRIGATION SWEET CORN YIELD WHERE NET
RETURNS WOULD BE EQUAL TO NET RETURNS FOR SPRINKLER AND FURROW
IRRIGATION BASED ON 1971-1973 DATA*
Nitrogen ' Manual subirrigationAutomated sub-irrigation
applied Sprinkler Furrow Sprinkler Furrow
^y
0
22.4 -
112
67.2
.0
38.
56.
63.
1
0
8
(99%)*
(24%)±
(32%)*
38.1
60.5
65.0
^u 1 1
(99%)%
(33*)*
(34%)
lua i
33.
66.
6
t
1
(37%)*
(48%)
31.
66.
4 (30%)t
t
1 (50%)t
*Basea on average operating costs for 1971-1973 and a sub-irrigation invest-
ment of $2,470/ha for a manual system and $2,790/ha for an automated system.
-(-Information not available.
^Percent indicates the percentage increase in yield under subirn'gation,
compared to Table 45 data, needed to equal yields presented in this table.
Total Yield Per Hectare--
Figure 191 shows the influence of the various criteria used as a basis
for applying irrigation water on the yield of sweet corn from the various
irrigation systems. In using the growth criteria, water was applied when
the first visual stress occurred. In the other treatments, water was applied
when a) the soil-water potential reached -20 to -30 cb and b) -40 to
-60 cb. It can be seen that the average yield increased approximately
2,000 ears/ha where tensiometers rather than growth was used as the criteria
for applying irrigation water. However, furrow irrigation system yields were
highest when growth rather than tensiometers were used as the criteria for
applying irrigation water. Yields from plots of sprinkler and subirrigation
systems were superior when tensiometers rather than growth were used as the
criteria for applying irrigation water. Growth was not a criteria for apply-
ing water to the automated subirrigation and trickle irrigation systems. The
yields from these systems were lower and little difference existed in tension
levels. These data suggest that more information is needed relative to
obtaining maximum yields from automated systems. No break-throughs in yield
were obtained with automated systems. In fact, the yields from non-automated
systems were, in general, superior to those from automated systems. It
should be borne in mind that these data are a summary of all treatments over
four years and that, in many cases, the yields of automated systems were
equal to those from non-automated systems.
The influence of the various fertilizer sources on the yield of sweet
corn from the various systems is shown in Figure 192. In general, the yield
of plots where the fertilizer was applied in the bed was superior to plots
where the fertilizer was applied in the irrigation water or in the furrow.
Yields of plots where ammonia was applied in the bed were higher than where
ammonia + N-Serve was applied in the bed. Yields from the various irrigation
systems were normally distributed around the mean of the yields with a few
exceptions. Yields where Uran was applied in the furrow in the furrow-
irrigated plots were superior to those from the subirrigated plots. Also,
312
-------
32
30
o
o
2 28
X
oo
o:
LU
o
LU
26
24
22
20
o-
o-
D -
A-
MEAN
FURROW
SPRINKLER
SUBIRRIGATION
AUTOMATED
SUBIRRIGATION
TRICKLE
j_
GROWTH
-20 TO -30 cb
POTENTIAL
-40 TO -60 cb
POTENTIAL
CRITERIA FOR APPLYING IRRIGATION WATER
Figure 191. Yield of sweet corn of different irrigation systems as
influenced by different irrigation criteria, 1971-1974,
Knox County, Texas.
313
-------
o
o
o
rc
oo
-------
yields of treatments of the sub-irrigated plots where ammonia was applied in
the furrow and in the bed with N-Serve were superior to those from the
furrow-irrigated plots.
In summary, there appears to be some advantage in irrigating on the
basis of soil-water potential rather than stage of growth of the crop.
Yields tended to be better, with the exception of the automated plots, in
most cases where the fertilizer was applied in the bed rather than the fur-
row or irrigation water. No major differences existed between fertilizer
sources when the sources were applied in the bed.
Yield Per Unit of Water--
There was little difference in the mean yield per cm of water of the
different irrigation criteria (Figure 193). The yields of the subirrigated
plots were greater than the mean yield where the yields from the automated
trickle plot were approximately equal to the mean. Yields of the furrow- and
sprinkler-irrigated plots were less than the mean except for the stage of
growth criteria in the sprinkler plot system and the -40 to -60 cb treatment
in the furrow-irrigated plot system. These data show that water can be more
efficiently used if applied in subirrigation systems than through sprinkler
and furrow irrigation systems.
If only the manual subirrigation systems are considered, there is little
difference in the mean yield per unit among fertilizer sources and methods of
applications with the exception of where the Uran was applied in the furrow
(Figure 194). Yields of the different irrigation systems were closely
distributed around the mean except in those treatments where ammonia +
N-Serve and ammonia were applied in the bed and Uran was applied in the irri-
gation water. In these treatments, yields (1,600 ears/cm/ha) of the subirri-
gation system were superior to those of the sprinkler and furrow irrigation
systems.
Yields/cm of water from the automated subirrigation systems were far
superior to those from other irrigation systems. In summary, yields/cm/ha
from the subirrigated plots were superior to the sprinkler- and furrow-
irrigated plots. Yields/cm/ha for the subirrigation systems with ammonia +
N-Serve applied in the bed, ammonia applied in the furrow, and Uran applied
in the water of the subirrigated plots were superior to similar treatments of
the furrow- and sprinkler-irrigated plots. The highest yields/cm/ha were
obtained when water was applied through automated subirrigation systems and
the crop was fertilized with Uran. Due to the major increase in irrigation
efficiency with automated systems, it appears that an investigation of the
potential of automating other irrigation systems would be worthwhile.
Yield Per Unit of Fertilizer— ....
The influence of the different criteria for applying irrigation water
on the yield per unit of nitrogen was erratic (Figure 195). Where growth was
used as the criteria for applying irrigation water, yields/unit of fertilizer
from the subirrigation systems were superior to those from the furrow and
sprinkler systems. The differences between systems were not large at -20 to
-30 cb potential. At -40 to -60 cb, the yield per unit of nitrogen was
greatest from the sprinkler plots, intermediate from the subirrigated and
315
-------
2.0
o 1.5
o
o
o
£1-0
-------
2.0-
o
o
o
CO
— - MEAN
O - FURROW
O - SPRINKLER
D - SUBIRRIGATION
A - AUTOMATED SUBIRRIGATION
@ - TRICKLE
A
O
_L
I
I
CONTROL
URAN
FURROW
UREA
BED
SODIUM
NITRATE
BED
AMMONIA +
N-SERVE
BED
AMMONIA
FURROW
AMMONIA
BED
URAN
IRRIGATION
WATER
FERTILIZER SOURCE
A
URAN
BED
Figure 194. Yield of sweet corn per cm of water of different irrigation systems as influenced by
different fertilizer sources and methods of application, 1971-1974, Knox County, Texas,
-------
6-
MEAN
FURROW
SPRINKLER
SUBIRRIGATION
AUTOMATED SUBIRRIGATION
TRICKLE
o
o
LU
CD
O
•
I
GROWTH -20 TO -30 cb -40 TO -60 cb
POTENTIAL POTENTIAL
CRITERIA FOR APPLYING IRRIGATION WATER
Figure 195. Yield of sweet corn of different irrigation systems
per kg of nitrogen applied at the 100 kg/ha rate as
influenced by different irrigation criteria,
1971-1974, Knox County, Texas.
318
-------
furrow plots, and lowest from the automatically-subirrigated plots.
Figure 196 shows there was little influence of fertilizer source or method
of application on the yield per unit of nitrogen where 100 kg/ha were
applied to all treatments.
Where 22.5 kg of nitrogen were applied per ha, there were major differ-
ences in the yield per unit of fertilizer applied (Figure 197). Yields/kg
of nitrogen of the different irrigation systems from the -20 cb plots were
superior to those of the -40 cb plots except for the automatically-
subirrigated plots. In the -20 cb plot system, yields per unit of nitrogen
from the furrow irrigation system were the highest, followed by yields of
the sprinkler system and automated subirrigation systems, with the lowest
yields being obtained from the subirrigated plots. In the -40 cb plots,
highest yields/unit of nitrogen were obtained from the automated subirri-
gation system followed by the furrow and sprinkler systems with the subirri-
gation systems again have the lowest efficiency. However, it should be
pointed out that, although the yields per unit of nitrogen are higher for
the 22.5 kg application rate, the highest yields were obtained with the
application of the highest rates of nitrogen.
In summary, when sources of fertilizer were applied at 100 kg/ha rates,
there was no significant difference in the yield per unit of nitrogen.
Differences among irrigation systems existed when less than optimal amounts
of nitrogen were applied in the irrigation water. However, maximum yields
were not obtained.
319
-------
OJ
ro
o
MEAN
O - FURROW
O - SPRINKLER
D - SUBIRRIGATION
o
X
2 a
84 -
a:
i — i
•z.
GO
I'" °
— i
LU
I — t
o - i
AMMONIA
FURROW
0
D
_— — - —
O
1
UREA
BED
O Q —
-^ °
1 «
AMMONIA + SODIUM
N-SERVE NITRATE
BED BED
§ 8
_— —
a
i t i
URAN AMMONIA
BED BED
FERTILIZER SOURCE
Figure 196. Yield of sweet corn of different irrigation systems per kg of nitrogen applied
at the 100 kg/ha rate as influenced by different fertilizer sources, 1971-1974.
-------
1400
o-
o-
D -
A -
1200
a:
1000
800
MEAN
FURROW
SPRINKLER
SUBIRRIGATION
AUTOMATED
SUBIRRIGATION
600
-20 cb -40 cb
IRRIGATION CRITERIA
Figure 197. Yield of sweet corn of different irrigation systems
per kg of nitrogen applied at the 22.5 kg/ha rate
as influenced by the different irrigation criteria,
1971-1974.
321
-------
SECTION 7
SUMMARY
A comparison of sprinkler, furrow, and manual subirrigation systems
showed that nitrate-N in soil samples and porous bulb extracts was much less
for samples from below the root zone from subirrigation systems than from
the sprinkler or furrow systems. Through analyses of 15N in soil and plant
materials it was possible to account for 92.6%, 86.1%, and 50.5%, respec-
tively, of the fertilizer nitrogen applied to the sprinkler, furrow, and
subirrigation systems over a two-year period. Soil-water potential, bromide
tracer, porous bulb extract, and soil data all support the idea that denitri-
fication occurs with subirrigation systems in that the major differences
between systems was the amount of soil nitrogen that could be detected. In
any case, less nitrate-N was available to be leached in the subirrigated
plots.
Where fertilizer was applied each year, 62%, 55%, and 49% of the fertil-
izer was used by corn from the sprinkler, furrow, and subirrigation systems,
respectively. As there was little difference in yield, the data indicate
that more than adequate fertilizer was applied even though the uptake per-
centages were different. The crop contained 2.0%, 3.6%, and 7.4% of the
fertilizer applied the previous year when grown under sprinkler, furrow,
and subirrigation, respectively. These data indicate that much of the
nitrogen from the previous year's crop was still in the organic form in
that only small amounts were available.
Movement of nitrate during and between growing seasons was noted, espe-
cially with the furrow and sprinkler irrigation plots. Data from 15N and
bromide tracer studies showed unique patterns of movement for the different
systems. Banded fertilizer moved vertically as discrete bands under the
sprinkler irrigation system. In the furrow irrigation system, the fertilizer
bands merged in the bed and then moved vertically. Fertilizer bands moved up
and away from the buried subirrigation system. In addition to being influ-
enced by irrigation system, the downward movement was influenced by soil
texture and the rainfall received between growing seasons.
By irrigating on the basis of potential ET, it was possible to maintain
nitrogen fertilizers in the root zone during the growing season. The ranking
of systems relative to irrigation water requirement was furrow > sprinkler =
subirrigation > automatic subirrigation. In general, the automated subirri-
gation system required water applications of only 50% to 60% of the sprinkler
and manual subirrigation systems and 30% to 40% of the furrow system. During
the study only 10 to 14 cm/year of supplemental water were applied through
322
-------
the automated system to produce the sweet corn crop, compared to 18 to
38 cm/year applied through the other systems. However, the differences among
systems relative to the total amount of water used by the crop was not sig-
nificant. Where less irrigation water was applied, more of the soil water
was used. The studies showed that the plots with automated subirrigation
maintained a portion of the soil profile (0 to 45 cm) with adequate moisture
through frequent irrigations of 0.25 cm or less and allowed the zone below
45 cm to dry. This created a zone for storage of rainfall and substantial
increases in irrigation water-use efficiency. The model of Jensen, et al.
(10) for ET potential combined with the ET at various LAI by Ritchie and
Burnett (21) proved adequate for estimating crop water requirements.
There was no difference in irrigation water requirement between systems
when irrigations were made on the basis of potential ET, if the system was
well designed. It was difficult to apply water in small amounts with the
furrow irrigation system on the loamy fine sand soil. Consequently, the water
added was greater than that indicated by potential ET. However, as previ-
ously discussed, the irrigation water requirement of the automated subirri-
gation system was significantly less than those of other systems even though
they were irrigated based on potential ET.
Solutes other than nitrate-N were measured to determine if their concen-
tration was influenced by irrigation system. Measurements were made of
nitrite, phosphate, chloride, sulfate, sodium, calcium, magnesium, ammonium
and potassium concentrations and conductivity. Nitrite and phosphate
measurements were discontinued after the first year due to low concentrations.
Porous bulb extracts from subirrigation systems were lower in chloride, sul-
fate, sodium, calcium, and magnesium concentrations and conductivity than the
furrow and sprinkler irrigation systems. The concentrations of the above-
mentioned ions and conductivity of extracts from the automated subirrigation
system were significantly lower than extracts from the other systems. In no
case was there an indication of any of these ions being a problem in degra-
dation of irrigation return flow in that the ion concentrations and the con-
ductivity of extracts in most cases were only slightly higher or less than
the ion concentrations and conductivity of the irrigation water. The data do
suggest, however, that manual and automatic subirrigation may have the poten-
tial to enhance the quality of irrigation return flows because a) the con-
centrations of ions and conductivity were significantly lower in the
application zone around the subirrigation pipe and b) significantly less
water was added through the automated subirrigation system; therefore,
significantly less salt was added.
Potassium was lowest in the furrow system due to land leveling. The ion
was indicated to be made available at a constant rate throughout the growing
season.
Although significant concentrations of ammonium were found periodically,
there was no consistent pattern relative to amount, location, and time so
that conclusions cannot be made concerning its presence.
The automated subirrigation system applied less water, but also produced
less total sweet corn yield. However, the yield per unit of water of the
323
-------
automated subirrigation system was significantly higher than the other
irrigation systems. Total yields of the manual subirrigation, furrow irriga-
tion, and sprinkler irrigation systems were approximately equal. The manual
subirrigation system was more efficient (yield/unit of water) than the sprin-
kler and furrow systems. There was no difference in nitrogen-use efficiency
(ears of corn/kg/ha) when 100 kg/ha/year were applied. When only small
amounts of nitrogen were applied (22.5 kg/ha), the manual subirrigation
system was less efficient than the other systems.
Although subirrigation systems show promise relative to enhancing the
quality of irrigation return flows and increasing water-use efficiency,
problems exist with the systems. The cost of the systems is high. Net
returns for the sprinkler, furrow, manual subirrigation, and automated sub-
irrigation were $166, $180, -$88, and -$172.90/ha, respectively. For the
subirrigation system to compete with the sprinkler and furrow systems, it
would have to cost, respectively, only $528 and $407/ha, compared to the
current cost of $2,470/ha. The $2,780/ha cost of the automated subirrigation
system would need to be decreased to $432 and $311/ha, respectively, to com-
pete with the sprinkler and furrow systems. Yields of the manual subirriga-
tion and automated subirrigation systems would need to be increased 33% and
50%, respectively, to compete with current furrow and sprinkler irrigation
systems.
Other problems with subirrigation systems include obtaining emergence
with bed planting, movement of banded fertilizer from the active root zone,
stoppage of orifices due to roots and soil particles, and miscellaneous
problems relative to gophers, valves, splitting pipes, and filtering. How-
ever, none of these are technically insurmountable.
Criteria used to apply irrigation water were a) curling of upper
leaves at midday, b) -20 cb soil-water potential at 30 cm, and c) -40 cb
soil-water potential at 30 cm. No differences in quality of irrigation
return flow were noted from using the different criteria. Total yield of
sweet corn was greater when the plots were irrigated at -20 cb potential
than at -40 cb or at leaf curling. No differences in yield/unit of water
were noted from using the different criteria. Yield/unit of nitrogen
applied was greater when the plots were irrigated at leaf curl and -40 cb
potential than at -20 cb potential.
Methods of fertilizer application evaluated in the studies were banded
below the level of the water furrow, banded above the level of the water
furrow, and applied through the irrigation water. In the furrow irrigation
system, the nitrate-N concentrations in soil samples and porous bulb samples
from below the root zone were higher where the fertilizer was banded below
the level of the water furrow. Significant losses of nitrogen occurred when
applied through the water in the sprinkler and subirrigation systems. Much
of the nitrogen banded over the subirrigation systems was not detected for
reasons previously discussed. However, since high rates of nitrogen were
applied, no differences were observed in yield/unit of water or yield/unit
of nitrogen due to method of application.
324
-------
Sources of fertilizer used in the study included anhydrous ammonia,
Uran, sulfur-coated urea, and ammonia + N-Serve. There was no distinct
advantage of any source relative to nitrate-N in irrigation return flows
total yield, yield/unit of water, or yield/unit of nitrogen.
The model by Hillel, et al. (9) for determining hydraulic conductivity
was evaluated. Values obtained varied for the same texture at different
depths and for the same depth for a given soil-water content and matric
potential when determined more than one time at the same location. Changes
of 100-fold in values for hydraulic conductivity occurred with 2% to 6%
changes in soil-water content. Water movement occurred within the soil pro-
file due to saturated pressure heads as well as unsaturated pressure
gradients.
Due to the problems with the above-mentioned variability, a regression
model was developed for hydraulic conductivity as a function of moisture
content, depth, and texture. The r value for the equation was .915. How-
ever, the standard error of estimate was so great that further use of the
equation was not deemed worthwhile.
An empirical model for nitrate movement as a function of rainfall, irri-
gation, fertilization, potential ET, LAI, uptake of nitrogen by the crop, and
the relationship for calculating ET as a function of leaf area was devised
using data obtained at the site. The most important parameters were found to
be the amount of irrigation water applied and total nitrate in the profile.
When water applied was greater than 2 to 2.5 x potential ET and nitrate-N in
the profile was greater than 200 kg/ha, the leachate concentration was
greater than 20 ppm nitrate-N. When irrigation water amounts were equal to
potential ET, no nitrate-N was leached. Less nitrogen was needed when irri-
gation water applications and rainfall equalled potential ET. In the absence
of excess rainfall, automated irrigation will keep nitrate-N in the root
zone. Turning under residue while the soil is still warm in the summer will
enhance nitrification and add nitrate-N to the leachate.
Bromide was found to be an excellent indicator of nitrate movement. An
excellent relationship was found between bromide depth and net water added to
the soil (R = .879). The relationship indicates that for each cm of excess
water added bromide or nitrate will move down 7.4 cm.
Some of the site characteristics are worthy of note in that they_influ-
ence parameters related to irrigation return flow. The soil at the site is
relatively uniform at the surface but varies considerably in texture and bulk
density with depth. The layering causes the soil to have a large amount of
water at field capacity (-10 cb instead of -33 cb). An excess of water is
needed to cause movement from one layer to the next. Highest water contents
and nitrate concentrations were found in or above zones of higher clay con-
tent. The soils are self-mulching so that adequate planting moisture can be
stored for 6 to 8 months, thus decreasing the irrigation water requirement
for emergence.
Some of the site characteristics are of interest since they may affect
water quality and irrigation return flows. The clay minerals are
325
-------
interstratified mixtures of montmoriHonite and illite and are the same from
the surface to the water table. Wells at the site received horizontal
recharge from the local aquifer. Large amounts of nitrate were found in
soil-water extracts (>50 ppm nitrate-N) on the control plots. Data from
the 15N studies show that the corn crop used 50 kg of nitrogen/ha from soil
nitrogen. Rainfall received during the study ranged from 483.0 to 596.2 mm
for 112.9-mm variation. Rainfall during growing seasons varied from 104.0
to 224.7 mm for a difference of 120 mm. Rainfall between growing seasons of
sweet corn was 2 to 4 times that received during the growing season. These
variations emphasize the importance of using some criteria other than stage
of growth for timing of irrigations and some method of determining amounts
to be applied in order to maintain the quality of irrigation return flows
with respect to nitrogen.
326
-------
REFERENCES
1. Bausch, W., A. B. Onken, C. W. Wendt, and 0. C. Wilke. A Self-propelled
High-Clearance Soil Coring Machine. Submitted to Agronomy Journal for
publication.
2. Bremner, J. M., and K. Shaw. Denitrification in Soil II: Factors Affect-
ing Denitrification. J. Agr. Sci., 51:40-52, 1958.
3. Bremner, J. M. Isotope-Ratio Analyses of Nitrogen-15 Tracer Investiga-
tions In: Methods of Soil Analyses, 2:1256-1286, published by American
Society of Agronomy, Madison, Wisconsin, 1965.
4. Comly, H. H. Cyanosis From Nitrate in Well Water. Amer. Med Assoc.
Jour., 129:112-116, 1945.
5. Fritz, S. Solar Radiation on Cloudless Days. Heating and Ventilating,
46:69-74, 1949.
6. Gray, R. M. A Study on the Effects of Institutions on the Distribution
and Use of Water for Irrigation in the Lower Rio Grande Basin. (Unpub-
lished Ph.D. dissertation, Department of Agricultural Economics, Texas
A&M University, College Station, Texas). 1971.
7. Harmsen, G. W., and G. J. Kolenbrander. Soil Inorganic Nitrogen. In
Soil Nitrogen Edited by W. V. Bortholomew and Francis E. Clak. Agronomy
Monograph No. 10. American Society of Agronomy, Inc., Madison, Wiscon-
sin, 1975.
8. Hillel, D. Soil and Water. Academic Press, Inc., Ill Fifth Avenue, New
York, New York 10003, p. 227, 1971.
9. Hillel, 0., J. D. Krentos, and Y. Stylianon. Procedure and Test of an
Internal Drainage Method for Measuring Soil Hydraulic Conductivity jm
situ. Soil Set., 114:395-400, 1972.
10. Jensen, M. E., C. W. Robb, and C. E. Franzoy. Scheduling Irrigation
Using Climate-Crop-Soil Data. J. Irrig. Drain., Div. Amer. Soc. Civil
Eng., 96:25-38, 1969.
11. Kissel 1, D. E., J. T. Ritchie, and Earl Burnett. Chloride Movement in
Undisturbed Swelling Clay Soil. Soil Sci. Soc. Amer. Proc., 37:21-24,
1973.
327
-------
12. Lacewell, R. D., and H. W. Grubb. Economic Evaluation of Alternative
Temporal Water Use Plans on Cotton-Grain Sorghum Farms in the Fine-
Textured Soils of the Texas High Plains. Texas Agr. Exp. Sta., Dept.
of Agr. Economics Tech. Rep. No. 70-3, 1970.
13. Lacewell, R. D., and W. F. Hughes. A Comparison of Capital Requirements
and Labor Use, Alternative Sprinkler Irrigation Systems, Texas High
Plains. Texas Agr. Exp. Sta., Dept. of Agr. Economics Information
Rep. 71-3, 1971.
14. Lacewell, R. D., 0. C. Wilke, and W. Bausch. Economic Implications of
Subirrigation and Trickle Irrigation in Texas. Water Resources Insti-
tute Spec. Rep. No. 4, 1972.
15. Law, J. P., and J. L. Witherow. Irrigation Residues: In: A Primer on
Agricultural Pollution. Soil Conservation Society of America, p. 11-13,
1971.
16. Maxey, K. F. Report on the Relation of Nitrate Nitrogen Concentrations
in Well Waters to the Occurrence of Methemoglobinemia in Infants. Natl.
Research Council. Bull. Sanitary Engr. and Environment, App. D,
p. 265-271, 1950.
17. Miller, D. E. Flow and Retention of Water in Layered Soils. Cons. Res.
Report No. 13, ARS-USDA, 1969.
18. Miller, D. E., and W. C. Bunger. Moisture Retention of Soil With Coarse
Layers in the Profile. Soil Sci. Soc. Amer. Proc., 27:716-717, 1963.
19. Ogilbee, W., and F. L. Osborne. Ground-water Resources of Haskell and
Knox Counties, Texas. Texas Water Commission, Bulletin 6209, 1962.
20. Onken, A. B., R. S. Hargrove, C. W. Wendt, and 0. C. Wilke. The Use of
a Specific Ion Electrode for Determination of Bromide in Soils. Soil
Sci. Soc. Amer. Proc., 39:1223-1225, 1975.
21. Ritchie, J. T., and E. Burnett. Dryland Evaporative Flux in a Subhumid
Climate: II. Plant Influences. Agron. J., 63:56-62, 1971.
22. Texas Agricultural Extension Service. Texas Crop Budgets. Texas Agr.
Ext. Ser., MP-1027, 1972.
23. Wendt, C. W., H. P. Harbert, III, W. Bausch, and 0. C. Wilke. Auto-
mation of Drip Irrigation Systems. Presented at 1973 Winter Meeting
ASAE, Chicago, Illinois, December 11-14, 1973, Paper No. 73-2505, 1974.
328
-------
PUBLICATIONS AND PRESENTATIONS
1. Hargrove, R. S., W. C. Bausch, A. B. Onken, and C. W. Wendt. The
Utilization of a Bromide Tracer for Comparison of Two Soil-Water Sampling
Techniques. Agron. Abstracts, 1972 Annual Meetings, Miami Beach, Florida,
October 29-November 2, 1972, p. 84, 1972.
2. Hargrove, R. S., and W. C. Bausch. The Use of a Bromide Tracer for Com-
parison of Fertilizer Leaching Rates. Agron. Abstracts, 1973 Annual
Meetings, Las Vegas, Nevada, November 11-16, 1973, 1973.
3. Onken, A. B., C. W. Wendt, 0. C. Wilke, W. Bausch, and L. Barnes. Influ-
ence of Irrigation Systems on Movement of Nitrogen Released From Sulfur-
coated Urea. Agron. Abstracts, 1974 Annual Meetings, Chicago, Illinois,
November 10-16, 1974, p. 152, 1974.
4. Onken, A. B., R. S. Hargrove, C. W. Wendt, and 0. C. Wilke. The Use of a
Specific Ion Electrode for Determination of Bromide in Soils. Soil Sci.
Soc. Amer. Proc., 39:1223-25, 1975.
5. Wendt, C. W., A. B. Onken, and 0. C. Wilke. Effects of Irrigation
Methods and Fertilizer on Potential Pollution of Groundwater by Nitrate
and Other Solutes. Proceedings of 9th Annual West Texas Water Resources
Institute Conference, pp. 55-66, 1971.
6. Wendt, C. W., A. B. Onken, and 0. C. Wilke. Subirrigation Studies in the
High and Rolling Plains of Texas. In: Proc. of Nat. Con. on Manag. Irri.
Agri. to Improve Water Quality, pp. 157-171, 1972.
7. Wendt, C. W., W. Bausch, 0. C. Wilke, and A. B. Onken. Influence of
Irrigation Systems on Irrigation Return Flow. Agron. Abstracts, 1973
Annual Meetings, Las Vegas, Nevada, November 11-16, 1973, p. 133, 1973.
8. Wendt, C. W., H. P. Harbert, III, W. Bausch, and 0. C. Wilke. Automation
of Drip Irrigation Systems. Presented at 1973 Winter Meeting ASAE,
Chicago, Illinois, December 11-14, 1973, Paper No. 73-2505, 1974.
9. Wilke, 0. C., A. B. Onken, and C. W. Wendt. A Model for Leaching of
Nitrate From Warm Sandy Soils. Presented at 1976 Spring Meeting of ASAE,
Baton Rouge, Louisiana, April 8, 1976.
329
-------
MANUSCRIPTS PREPARED AND SUBMITTED
1. Bausch, W.§ A. B. Onken, C. W. Wendt, and 0. C. Wilke. A Self-
propelled High-clearance Soil Coring Machine. Submitted to the
Agronomy Journal.
2. Onken, A. B., C. W. Wendt, R. S. Hargrove, and 0. C. Wilke. Relative
Movement of Bromide and Nitrate Under Three Irrigation Systems. Sub-
mitted to Soil Science Society of America Journal.
330
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
PA-600/2-76-291
I 2.
. TITLE AND SUBTITLE
EFFECTS OF IRRIGATION METHODS ON GROUNDWATER
POLLUTION BY NITRATES AND OTHER SOLUTES
6. PERFORMING ORGANIZATION CODE
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
December 1976 (Issuing Date)
. AUTHOR(S)
harles W. Wendt, Arthur B. Onken, Otto C. Wilke,
and Ronald D. Lacewell
8. PERFORMING ORGANIZATION REPORT NO.
. PERFORMING ORGANIZATION NAME AND ADDRESS
Texas Agricultural Experiment Station
Route 3
Lubbock, Texas 79401
10. PROGRAM ELEMENT NO.
1HB617
11. CONTRACT/GRANT NO.
Grant No. S-802806
(Formerly 13030 EZM)
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Res. Lab.
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
13. TYPE OF REPORT AND PERIOD COVERED
- Ada, OK
Final
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
^.ABSTRACT Sprinkler irrigation, furrow irrigation, subirrigation, automated sub-
irrigation, criteria for applying irrigation water, methods of applying fertilizer and
sources of fertilizer were investigated as to their potential to decrease possible
pollution from nitrate and other solutes in a loamy fine sand soil overlying a shallow
aquifer in Knox County, Texas.
Less nitrate-nitrogen was available for leaching in subirrigation systems than
furrow and sprinkler systems. Less irrigation water was applied with automated
subirrigation systems than with the other irrigation systems. However, crop water
requirement was not significantly changed—the soil water was more efficiently used.
Fertilizer remained in the root zone if the water applied was based on potential
evapotranspfration and leaf area regardless of the irrigation system or the criteria
used to apply the irrigation water. Banded fertilizers moved differently in the
different irrigation systems.
Subirrigation has the possibility of having irrigation return flow with lower
concentrations of other solutes than sprinkler or furrow systems.
Banding fertilizer in the bed was superior to banding below the level of the wate
furrow and applications in the irrigation water relative to quality of irrigation retur
flow. No other source of nitrogen fertilizer was indicated to be superior.
Current fertilization practices are not causing major increases in the nitrate-
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
Irrigation, Fertilizers, Nitrogen,
Isotopes, Water pollution, Soil water
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
Sprinkler irrigation,
Surface irrigation,
Subsurface irrigation.
Nitrate movement,
N-15 isotope,
Irrigation efficiency
19. SECURITY CLASS (This Report)
Unclassified
EPA Form 2220-1 (9-73)
20 SECURITY CLASS (This page)
Un classified
"331'
COSATi Field/Group
02C
21 NO. OF PAGES
359
22. PRICE
i U.S. GOVERNMENT PRINTING OFFICE: 1977— 757-056/560Z
------- |