EPA-600/2-77-177
August 1977
Environmental Protection Technology Series
FERTILIZER AND PESTICIDE MOVEMENT FROM
CITRUS GROVES IN FLORIDA
FLATWOOD SOILS
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30605
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en- '
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technicallnforma-
tion Service, Springfield, Virginia 22161.
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FERTiliZER AND PESTICIDE MOVEMENT FROM CITRUS
GROVES IN F~ORIDA FlATWOOD SOilS
by
R. S . Mansell
D. V. Calvert
E. H. Stewart
W. B. Wheeler
J. S. Rogers
D. A. Graetz
l. H. Allen
A. R. Overman
E. B. Kn i pI i ng
University of Florida
Gainesville, Florida 32611
Grant No. R-800517
Project Officer
lee A. Mulkey
Technology Development and Appl ication Branch
Environmental Research laboratory
Athens, Georgia 30605
ENVIRONMENTAL RESEARCH lABORATORY - ATHENS
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30605
EPA-600/2-77-177
August 1977
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory,
U.S. Environmental Protection Agency and approved for publ ication. Approval
does not signify that the contents necessarily reflect the views and poli-
cies of the U.S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendation for
use.
i i
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FOREWORD
Environmental protection efforts are increasingly directed towards pre-
venting adverse health and ecological effects associated with specific com-
pounds of natural or human origin. As part of this Laboratory's research on
the occurrence, movement, transformation, impact, and control of environ-
mental contaminants, the Technology Development and Appl ications Branch
develops management or engineering tools for assessing and controlling
adverse environmental effects of non-irrigated agriculture and silviculture.
This study was conducted to investigate the influence of appl ied ferti-
I izers and pesticides upon the water qual ity of surface and subsurface
drainage. Various soil management practices, particularly tillage systems,
were evaluated as controls for losses of fertil izer and pesticide from the
rapidly expanding citrus groves of southern Florida. If guidelines
furnished here are followed, citrus grove managers can make more efficient,
cost-effective use of fertil izers and herbicides and, at the same time,
reduce the contribution of this non-point source of pollution to our water-
ways.
David W. Duttweiler
Director
Environmental Research
Athens, Georgia
Laboratory
i i i
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ABSTRACT
Concentrations and discharge amounts of N03-N, P04-P, 2,4-D herbicide,
terbacil herbicide, and chlorobenzilate acaricide were determined in surface
and subsurface drainage waters from a citrus grove located in an acid, sandy
flatwood soil of southern Florida. The citrus grove received routine appl i-
cations of fertil izer, pesticide, and irrigation water as needed. The grove
was established in 1970 by placing trees in two rows on top of soil beds
which were separated by furrows for surface runoff. Subsurface plastic
drain tubes placed at 107 cm depth and spaced 18.3 m apart were installed
perpendicular to the soil beds.
The influence of fertil izer and pesticide upon water qual ity was examined
for citrus growing in three soil management treatments: ST, DT, and DTL.
The ST or shallow-tilled plot was plowed to 15 cm depth, the DT or deep-
tilled plot was establ ished by mixing the top 105 cm of the soil profile with
a trenching machine, and the DTL plot was also deep tilled to a depth of 105
cm with 56 mt/ha of dolomitic 1 imestone mixed with the soil. A drained
untilled, unfertil ized control plot without citrus was also established.
Following an individual rainfall or irrigation event, water flux from
subsurface drains as well as drawdown of the water table at the midplane
between parallel drains were consistently greater from the shallow-tilled
plot relative to the deep-tilled plots. However, drainage from DT was more
rapid than from DTL. Average annual quantities of drainage from ST was
equivalent to 50% of total rainfall plus irrigation. For DT and DTL plots
drainage water represented only 28 and 17%, respectively, of total water inaut.
Routine applications of fertil izer increased concentrations of N03-N and
P04-P in drainage water from all three plots. Greatest leaching losses of
these nutrients occurred from ST. Average annual losses of N03-N in both
surface and subsurface drainage from ST, DT, and DTL plots were equivalent
to 22.1, 3.1, and 5.4% of total N applied as fertil izer. Average annual
losses of P04-P in both surface and subsurface drainage from ST, DT, ~nd DTL
plots were equivalent to 16.9, 3.6, and 3.5% of total P applied.as fertil i-
zero Deep tillage was thus observed to greatly decrease leaching loss of N
and P nutrients. Loss of nutrients in surface runoff was very small for all
three plots.
Although the magnitudes were less, deep tillage also decreased leaching
losses of terbacil and 2,4-D herbicide. Discharges of these herbicides in
subsurface drainage were usually in the order: ST> DTL> DT. Discharge of
2 4-D was greater from drains with open outlets than from drains with sub-
m~rged outlets. Better aeration in soil :urrounding open.drains was bel ieved
to have enhanced microbiological degradation of 2,4-D. Discharge of terba-
cil, which has a tenfold greater half-l ife than 2,4-D, did not differ for
iv
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open and submerged drains. Chlorobenzilate pesticide was not detected in
drainage water from any of the three soil treatments.
This report was submitted in fulfillment of Grant No. R-800517 by the
Institute of Food and Agricultural Sciences of the University of Florida
under the sponsorship of the U.S. Environmental Protection Agency. This
report covers a period from May 1, 1973 to December 31, 1976, and work was
completed as of April 1, 1977.
v
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CONTENTS
Section
Page Number
Foreword
. .. . . . . . . . . . . . .
i i i
Abstract
.. .. . . . . 0
. . . .
. . . . . . . .
. . . .
iv
Figures
. . . . .. ..
.. .. . ..
.. .. . .. .. .. . . .. ..
ix
Tables.
. .. . .
.. .. .. . .. .. .
.. . .. . . .. .
. . .. . .. .. . ..
xvi I
Acknowledgment
.. . .. .. . .. .. .
.. .. .. . .. ..
.. .. . . . ..
xxi
I.
introduction. . . . . . . . .
.. .. .. .. .. ..
. .. .. ..
.. . . .. ..
II.
Conclusions
.. .. .. .. .. .. . .. .. ..
.. .. .. ..
.. . .. ..
5
III.
Recommendations
.. .. . ..
.. .. . .. ..
.. . .. ..
9
IV.
Concentration and Flux of N03-N and P04-P in Surface and
Subsurface Drainage Water from a Fertilized Citrus Grove
Experimental Methods and Procedure
.. .. . .. .. .. . ..
12
Results and Discussion
Summary. .
. .. .. .. .. .. ..
.. .. .. .. .. .. . . ..
. .. . ..
19
74
.. .. .. .
.. .. ...
V.
Concentrations and Flux of Chlorobenzilate Acaricide and Terba-
cil and 2,4-Dichlorophenoxyacetic Acid Herbicides in Surface
and Subsurface Drainage Water from a Citrus Grove
Experimental Methods and Procedure
.. .. . .
.. .. .. ..
78
Results and Discussion
.. . .. .. .. .. ..
.. .. .. .. .. .. ..
80
Summa ry . .
.. .. .. .. .. .. ..
.. .. .. .. .
. . . .. .
91
VI.
Denitrification in Shallow- and Deep-tilled Spodosol
Experimental Methods and Procedure
Results and Discussion
.. .. . .. .. . .
.. .. . . .. ..
.. .. .. ..
95
<36
.. .. .. .. .
Summary. .
.. .. . .. .. ..
.. .. .. .. .. ..
.. . .. .. .. .. . . . .. ..
101
vi i
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Section
VII.
VIII.
CONTENTS (CON'T)
Distributions of N03-N Concentration and Water Pressure in
Deep-Tilled Spodosol Following Fertilization and Irrigation
of a Citrus Grove
Experimental Methods and Procedures. .
. . . . . .
Results and Discussion
. . . 0
. . . .
Summa ry . .
. . . .
. . . .'"
. . . . . .
Phosphorus Adsorption-Desorption and Transport in Soil Columns
Laboratory Experiments
. . . . .
. . . . .
. . . .
A Mathematical Model For Transport and Transformation of
Phosphorus in So i 1 ...................
References
. . . .
. . . .
. . . . . . . .
Appendix:
Titles and Abstracts of Published Papers Resulting
from this Research. . . . . . . . . . . . . . .
vi i i
Page Number
104
104
105
119
119
125
130
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N um be r
1 °
FIGURES
Map of Florida showing locations of major areas of Spodosols.
2
Schematic diagram of the SWAP field experiment located at the
Agricultural Research Center, Florida Agricultural Experi-
ment Station, Fort Pierce, Florida. Locations for nine samp-
1 ing sites are shown.
3
Schematic diagram of a single main plot showing spl it plots
(submerged and open drains). Dots indicate the location
of citrus trees on beds.
4
Total monthly discharges of drainage water, N03-N, and P04-P
from ST, OT, and OTL soil management plots plotted with
time for 1973.
5
Total monthly discharges of drainage water, N03-N, and P04-P
from ST, OT, and OTL soil management plots plotted with
time for 1974.
6
Total monthly discharges of drainage water, N03-N, and P04-P
from ST, OT, and OTL soil management plots plotted with
time for 1975.
7
Total monthly amounts of rainfall and irrigation for ST, DT,
and OTL plots plotted with time for the period 1973-1975.
8
Total annual quantities of surface and subsurface drainage
plotted versus total amounts of rainfall plus irrigation
for ST, OT, OTL, and Control soil management plots for
the period 1973-1975.
9
Estimated annual amounts of water used in evapotranspiration
versus total amounts of rainfall plus irrigation for ST,
OT, OTL, and Control soil management plots for the period
1973-1975. .
Total N03-N discharged annually with surface and subsurface
drainage water versus total amounts of rainfall plus irri-
gation for ST, OT, DTL, and control soil management plots
for the period 1973-1975.
ix
Page
4
13
15
26
27
28
33
34
35
36
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-
FIGURES (continued)
Number
15
16
17
Page
II
Total P04-P discharged annual Iy w~th surface and subsurface
drainage water versus total amo~nts of rainfall plus irri-
gation for ST, DT, DTL, and Control soil management plots
for the period 1973-1975.
43
12
Monthly amounts of subsurface drainage plotted versus amounts
of rainfall plus irrigation for the ST soil treatment during
the period 1973-1975. The dotted I ine has a zero intercept
and a unit slope, and the solid I ine was obtained using I in-
ear regression. The regression equation is presented in
Table 16.
47
13
Monthly amounts of subsurface drainage plotted versus rainfall
plus irrigation for the DT plot during the period 1973-1975.
The dotted I ine has a zero intercept and a unit slope, and
the solid I ine was obtained using I inear regression. The
regression equation is presented in Table 16.
47
14
Monthly amounts of subsurface drainage plotted versus rainfall
plus irrigation for the DTL plot during the period 1973-1975.
The dotted I ine has a zero intercept and a unit slope, and
the sol id I ine was obtained using I inear regression. The
regression equation is presented in Table 16.
48
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment during a 14-day period (March 6-19,
1974) following 16.0-cm irrigation. Water was applied con-
tinuously over a 39-hour period immediately after a quart-
erly appl ication of 530 kg/ha of an 8-2-8 fertil izer. Rain-
fall occurred on days 9 and 10 for a total of 2.4 em.
51
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DT soil
management treatment during a 14-day period (March 6-19,
1974) following a 16.0-cm irrigation. Water was appl ied
continuously over a 39-hour period immediately after a
quarterly appl ication of 530 kg/ha of an 8-2-8 fertil izer.
Rainfal I occurred on days 9 and 10 for a total of 2.4 em.
52
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DTL soil
management treatment during a 14-day period (March 6-19,
1974) following a 16.0-cm irrigation. Water was appl ied
continuously over a 39-hour period immediately after a
quarterly appl ication of 530 kg/ha of an 8-2-8 fertil izer.
Rainfall occurred on days 9 and 10 for a total of 2.4 em.
53
x
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FIGURES (continued)
Number
20
21
22
23
18
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment durinq a 14-day period (May 21 through
June 3, 1974) following an 8.2-cm irrigation. Water was
appl ied continuously over a 20-hour period immediately after
a quarterly appl ication of 530 kg/ha of an 8-2-8 fertil izer.
Rainfall occurred on days 13 and 14 for a total of 2.7 em.
19
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DT soil
management treatment durinq a 14-day period (May 21 through
June 3, 1974) following an S.2-cm irrigation. Water was
app1 ied continuously over a 20-hour period immediately after
a quarterly application of 530 kg/ha of an 8-2-8 ferti1 izer.
Rainfall occurred on days 13 and 14 for a total of 2.7 em.
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DTL soil
management treatment during a 14-day period (May 21 through
June 3, 1974) following an 8.2-cm irrigation. Water was
applied continuously over a 20-hour period immediately after
a quarterly appl ication of 530 kg/ha of an 8-2-8 fertilizer.
Rainfall occurred on days 13 and 14 for a total of 2.7 em.
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment during a 14-day period (March 17-30,
1975) fo1 lowing a 2.4-cm irrigation. Water was applied
continuously over a 6-hour period immediately after a quart-
erly application of 530 kg/ha of an 8-2-8 ferti1 izer. Rain-
fall occurred on days 2 and 3 for a total of 2.9 em.
Fluxes of drainage water and N03-N and concentrations of N03-N
in subsurface drainage from the DT soil management treatment
during a 14-day period (March 17-30, 1975) following a 2.4-
em irrigation. Water was applied continuously over a 6-
')Our period immerJiate1y after a quarterly app1 ication of
530 kg/ha of an 8-2-8 ferti1 izer. Rainfall occurred on
days 2 and 3 for a total of 2.9 em. Concentrations of
fluxes of P04-P were very small and are not shown on the
figure.
F1 uxes of d ra i nage water and rJOrN and concent rat ions of
N03-N in subsurface drainage from the DTL soil management
treatment during a 14-day period (March 17-30, 1975) fol-
lowing a 2.4-cm irrigation. Water was applied continuously
over a 6-hour period immediately after a quarterly app1 ica-
tion of 530 kg/ha of an 8-2-8 ferti1 izer. Rainfall occurred
xi
Page
54
55
56
57
58
59
-------
FIGURES (continued)
Number
24
25
26
27
28
29
on days 2 and 3 for a total of 2.9 em. Concentrations and
fluxes of P04-P were very small and are not shown on the
figure.
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment during a 14-day period (February 11-24,
1975) following a 5.7-cm irrigation. Water was app1 ied
continuously over a 14-h~br period which occurred three
months after a quarter1yapp1 ication of 530 kg/ha of an 8-2-
8 ferti1 izer. Rainfall occurred on days 11 and 13 for a
total of 8.6 em.
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DJ ~~i1
management treatment during a 14-day period (February 11-
24, 1975) following a 5.7-cm irrigation. Water was app1 ied
continuously over a 14-hour period which occurred three
months after a quarterly app1 ication of 530 kg/ha of an 8-
2-8 ferti1 izer. Rainfall occurred on days 11 and 13 for a
total of 8.6 cm.
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DTL soil
management treatment during a 14-day period (February 11-
24, 1975) following a 5.7-cm irrigation. Water was applied
continuously over a 14-hour period which occurred three
months after a quarterly app1 ication of 530 kg/ha of an 8-
2-8 ferti1 izer. Rainfall occurred on days 11 and 13 for a
total of 8.6 cm.
Total drainage, N03-N discharged, and P04-P discharged versus
total rainfall and irrigation during three 14-day periods
(16.0, 8.2, and 2.4 cm irrigations) for ST, DT and DTL soil
management treatments.
Time-dependence of water table depth measured at a point mid-
way between two para1 leI drain tubes for a 16.0-cm irriga-
tion (Harch 6-14, 1974) in ST, DT, and DTL plots. The water
table depth is taken as a distance beneath a point of zero
depth located midway between the elevations of the surface
nf the soil bed and the bottom of the water furrow. The
elevations of the zero depth relative to mean sea level
were 6.40 m for the ST and DTL plots and 6.28 m for the DT
plot.
Time-dependence of water table depth measured at a point mid-
way between two parallel drain tubes for an 8.2-cm irrigation 72
xi i
Page
60.
61
62
70
n
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FIGURE (continued)
Number
39
40
41
(May 21-29, 1974) in ST, DT, and DTL plots.
30
Time-dependence of water table depth measured at a point mid-
way between two parallel drain tubes for a 5.7-cm irriga-
tion (February 11-19, 1975) in ST, DT, and DTL plots.
31
Structural formulas for chlorobenzilate, 2,4-D, and terbacil
pesticides.
32
Terbacil concentrations in water from submerged drains in ST,
DT, and DTL plots during the period March 6 to May 11, 1974.
33
Terbacil concentrations in water from open drains in ST, DT
and DTL plots during the period March 6 to May 11, 1974.
34
Concentrations of 2,4-D in water from submerged drains in
ST, DT, and DTL plots during the period March 6 to May 11,
1974.
35
Concentrations of 2,4-D in water from open drains in ST, DT
and DTL plots during the period March 6 to May 11, 1974.
36
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the ST plot during a 14-
day period (March 6-19, 1974) following a l6.0-cm irriga-
tion.
37
Water flux, terbacil concentration, and terbacil flux in
water from an open drain in ST, DT, and DTL plots during
a l4-day period (March 6-19, 1974) following a 16.0-cm
i r r i ga t ion.
38
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the DT plot during a 14-
day period (March 6-19, 1974) following a l6.0-cm irriga-
tion.
Water flux, terbacil concentration, and terbacil flux in
water from an open drain in the DT plot during a l4-day
period (March 6-19, 1974) following a l6.0-cm irrigation.
Water flux, terbacil concentration, and terbacil flux in water
from a submerged drain in the DTL plot'during a l4-day
period (March 6-19, 1974) following a l6.0-cm irrigation.
Water flux, terbacil concentration, and terbacil flux in
water from an open drain in the DTL plot during a l4-day
period (March 6-19, 1974) following a l6.0-cm irrigation.
xi i i
Page
73
79
81
81
82
82
83
83
84
84
85
85
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FIGURES (continued)
Number
45
46
47
48
49
50
51
52
42
Water flux, 2,4-0 concentration, and 2,4-D flux in water from
a submerged drain in the ST plot during a 14-day period
(March 6-19, 1974) following a 16.0-cm irrigation.
43
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from
an open drain in the ST plot during a 14-day period (March
6-19, 1974) following a 16.0-cm irrigation.
44
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from
a submerged drain in the OT plot during a 14-day period
(March 6-19,1971+) following a 16.0-cm irrigation.
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from
an open drain in the OT plot during a 14-day period (March
6-19, 1974) following a 16.0-cm irrigation.
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from
a submerged drain in the OTL plot during a 14-day period
(March 6-19, 1974) following a 16.0-cm irrigation.
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from
an open drain in the OTL plot during a 14-day period (March
6-19, 1974) following a 16.0-cm irrigation.
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the ST plot during a 14-
day period (March 17-31, 1975) following a 2.4-cm irriga-
tion.
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the DT plot during a 14-day
period (March 17-31, 1975) following a 2.4-cm irrigation.
Water flux, terbacil concentration, and terbacil flux in water
from a submerged drain in the OTL plot during a 14-day per-
iod (March 17-31, 1975) following a 2.4-cm irrigation.
Quantities of subsurface drainage and terbacil discharged with
drainage water versus the amounts of rainfall plus irriga-
tion received for 14-day periods following irrigation of ST,
OT, and OTL soil management plots.
Concentrations of N03-N in soil-water suspensions prepared
with soil samples removed from 0-30, 30-66, 66-81, and 81-
90 cm in the ST plot and anaerobically incubated for 24
days. The concentration of the appl ied N03-N solution
was 50 ]Jg/ml.
xiv
Page
86
$36
87
87
88
88
89
90
90
92
98
-------
FIGURES (continued)
Number
53
54
55
56
57
58
59
60
61
62
63
64
65
Concentrations of N03-N in soil-water suspensions prepared
with soil samples removed from 0-30, 30-60, and 60-90 cm
in the DT plot and anaerobically incubated for 24 days.
The concentration of the applied N03-N solution was 50
llg/m 1 .
Concentrations of N03-N in soil-water suspensions
with soil samples removed from 0-30, 30-60, and
in the DTL plot and anaerobically incubated for
The concentration of the applied N03-N solution
llg/ml.
prepared
60-90 cm
24 days.
was 50
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 3:00 PM on June 10, 1975.
Lines of equal water pressure are shown.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 9:50 PM on June 10, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 1:10 AM on June 11, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 2:15 PM on June II, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 4:00 PM on June 12, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 7:45 AM on June 13, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain on June 16, 1975.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain on June 18, 1975.
Spatial distribution of N03-N concentration in the solution
of DTL soil surrounding a subsurface drain at noon on
June 10, 1975. Lines of equal concentration are shown.
Spatial distribution of N03-N concentrations in the solution
of DTL soil surrounding a subsurface drain at midnight on
June 10, 1975.
Spatial distribution of N03-N concentrations in the solution
of DTL soil surrounding a subsurface drain at 9:30 AM on
June II, 1975.
xv
Page
99
100
105
106
107
108
109
110
111
112
113
114
115
-------
Figures (continued)
Number
66
67
68
69
70
71
72
73
Spatial distribution of N03-N concentration in the solution
of DTL soil surrounding a subsurface drain at 2:00 PM on
June 11, 1975.
Spatial distribution of N03-N concentration in the solution
of DTL soil surrounding a subsurface drain at 10:00 PM on
June 12, 1975.
Flux of subsurface drainage and N03-N concentration in the
drainage water from the DTl plot with time during the 14-
day period from June 10-24, 1975.
Experimental data and predicted breakthrough curves (Mansell
et al. 1977) for phosphorus concentrations in aqueous.
effluent eluted from a water-unsaturated core of subsur-
face (A2) Oldsmar sand.
Experimental data and predicted breakthrough curves (Mansell
et. al. 1977) for phosphorus concentrations in aqueous
effluent eluted from a water-unsaturated core of subsurface
(Al) Oldsmar sand.
A schematic diagram of a mechanistic multistep mathematical
model (Mansell, Sel im and Fiskell, 1977) for transforma-
tions of P applied to soil.
Distributions of solution and sorbed phases of applied P
during miscible displacement through a 100 cm long column of
a theoretical soil using a mechanistic, multistep kinetic
model (Mansell, Sel im, and Fiskell, 1977).
Total quantities of soluble, adsorbed, immobilized,
pitated phase P in a 100 cm column of theoretical
time during miscible displacement as predicted by
of Mansell, Selim, and Fiskell, (1977).
and preci-
so i 1 wit h
the mode 1
xvi
Page
116
117
118
120
121
122
123
124
-------
Number
1 °
TABLES
Selected physical and chemical properties of representative
profile horizons sampled from Oldsmar sand at the SWAP citrus
grove near Fort Pierce, Florida.
2
Fertil izer N, P, K, and Mg appl ied per hectare to ST, DT and
DTL treatments at the SWAP citrus grove near Fort Pierce,
Florida.
3
Rainfall recorded daily at the SWAP citrus grove near Fort
Pierce, Florida during 1973.
4
Rainfall recorded daily at the SWAP citrus grove near Fort
Pierce, Florida during 1974.
5
Rainfall recorded daily at the SWAP citrus grove near Fort
Pierce, Florida during 1975.
6
Mean monthly concentrations and total discharges of N03-N and
P04-P per hectare in subsurface drainage water in the ST
soil management treatment during 1973-1975 as a function of
rainfall, irrigation, total drainage, and mean water table
height (W.T. Ht.).
7
Mean monthly concentrations and total discharges of N03-N and
P04-P per hectare in subsurface drainage water in the DT
soil management treatment during 1973-1975 as a function of
rainfall, total drainage, and mean water table height.
8
Mean monthly concentrations and total discharges of N03-N and
P04-P per hectare in subsurface drainage water in the DTL
soil management treatment during 1973-1975 as a function of
rainfall, total drainage, and mean water table height.
9
Six-month means for N03-N and P04-P concentrations and discharge
in subsurface drainage from ST, DT, and DTL soil management
treatments as influenced by rainfall and total drainage.
Data for six-month wet periods (May through October) are pre-
sented for 1973-1975.
Six-month means for N03-N and P04-P concentrations and discharge
in subsurface drainage from ST, DT, and DTL soil management
xv i i
Page
14
18
20
21
22
23
24
25
31
32
-------
TABLES (continued)
Number
11
12
13
14
15
16
17
18
treatments as influenced by rainfall and total drainage.
Data for six-month dry period (November through April) are
presented for 1973-1975.
Mean monthly
in surface
treatments
1975.
concentrations and discharges of N03-N and P04-P
runoff water from ST, DT, and DTL soil manaqement
as a function of rainfall, during 1973,1974, and
Mean monthly concentrations and discharges of N03-N and P04-P
in subsurface drainage water from the unfertil ized Control
plot, Central Sump, and South Sump as a function of rainfall ,
drainage, and water table height (W.T.Ht.) during 1973, 1974,
1975.
Total annual quantities of rainfall irrigation, drainage, sur-
face runoff, estimated evapotranspiration, N03-N discharged
in drainage and runoff, and P04-P discharged in drainage and
runoff for ST, DT, and DTL soil management plots during 1973,
1974, and 1975.
Total annual quantities of rainfall, irrigation, drainage, esti-
mated evapotranspiration, N03-N discharged in drainage, and
P04-P discharged in drainage for the Control soil management
plot during 1973-1975.
Total annual quantities of rainfall plus irrigation, water,
N03-N, and P04-P discharged from the Central ~ump and ~outh
Sump of the SWAP citrus grove during 1973, 1~74, and 1975.
Linear regression equations relating D, monthly subsurface
drainage (cm), and I, mont~ly rainfall plus irrigation (cm),
for ST, DT, and DTL plots for the period 1973, 1974, and 1975.
Average fruit yields of Pineapple Orange growing in ST, DT,
and DTL treatment plots during 1975-1976 and calculated
amounts of N, P, and K in the harvested fruit. Calculations
were based upon the publ ication of Reitz (1961) who stated
that 1000 boxes (90 lbs. per box) of oranges contain 179.20
kg' of N, 22.48 kg of P, and 269.62 kg of K.
Concentrations and fluxes of N03-N and P04-P in subsurface
drainage water from ST, DT, and DTL treatments during a 14-
day period (t~arch 6-19, 1974) following a 16-cm irrigation.
The plots were irrigated continuously over a 39-hour period
immediately after a quarterly appl ication of 530 kg/ha of
an 8-2-8 fertil izer (42.38 kg/ha of Nand 4.62 kg/ha of p).
Rainfall also occurred on days 9 and 10. Water table heights
xv. i i i
Page
38
40
III
42
45
48
48
63
-------
TABLES (continued)
Number
22
23
24
25
26
are presented.
19
Concentrations and fluxes of N03-N and P04-P in subsurface drain-
age water from ST, OT, and OTL treatments during a 14-day per-
iod (May 21 through June 3, 1974) following an 8.2-cm irriga-
tion. The plots were irrigated continuously over a 20-hour
period immediately after a quarterly application of 530 kg/ha
of an 8-2-8 fertil izer. Rainfall occurred on days 13 and 14.
Water table heights are presented.
20
Concentrations and fluxes of N03-N and P04-P in subsurface drain-
age water from ST, OT, and OTL treatments during a 14-day per-
iod (March 17-30, 1975) following a 2.4-cm irrigation. The
plots were irrigated continuously over a 6-hour period immedi-
ately following a quarterly application of 530 kg/ha of an 8-
2-8 fertil izer. Rainfall occurred on days 2 and 3. Water
table heights are presented.
21
Concentrations and fluxes of N03-N and P04-P in subsurface drain-
age water from ST, OT, and OTL treatment during a 14-day per-
iod (February 11-24, 1975) following a 5.7-cm irrigation.
Plots were irrigated continuously over a 14-hour period which
occurred 3 months after a quarterly application of 530 kg/ha
of an 8-2-8 fertil izer. Rainfall occurred on days 11 and 13.
Depths to the water table are presented.
Concentrations, total discharges, and estimated percentage
losses of N03-N and P04-P in surface runoff water and subsur-
face drainage for 14-day periods following irrigation amounts
of 16.0, 8.2, 5.7, and 2.4 cm.
Dates and quantities of 2,4-0, terbacil, and chlorobenzilate
appl ied to ST, OT, and OTL experimental plots.
Quantities of 2,4-0 and terbacil pesticides discharged in sub-
surface drainage waters from ST, OT, and DTL soil management
plots during 14-day periods following an irrigation of 16.0
cm (plus 2.41 cm of rain) during March 6-19, 1974 and 2.4 cm
(plus 2.93 cm of rain) during March 17-31, 1975. Data is
presented for subsurface drains with open and submerged out-
lets.
Concentrations (Wg/kg) of terbacil and chlorobenzilate pesti-
cides in ST, OT, and OTL surface soil prior to and immedi-
ately following an application of these chemicals.
Total quantities of terbacil and 2,4-0 discharged in subsurface
drainage water from ST, OT, and OTL plots during 14-day per-
xix
Page
64
65
66
67
78
93
93
94
-------
TABLES (continued)
Number
iods following sequences of herbicide application and irri-
gation. Discharges were measured from single drain tubes,
which each drained areas of approximately 0.1673 hectares.
27
Half-lives for ch1orobenzi1ate, terbaci1, and 2,4-0 pesticides
incubated in several soil substrates.
28
Physical and chemical characteristics of ST, DT, and DTL soil
samples from the SWAP citrus grove.
29
Redox potentials observed during anaerobic incubation of the
ST soil samples.
30
Redox potentials observed during anaerobic incubation of the
DT soil samples.
31
Redox potentials observed during anaerobic incubation of the
DTL soil samples.
32
Redox potentials measured in subsurface drainage water during
the March, 1974 samp1 ing period.
33
In situ redox potentials of ST, DT, and DTL soils during the
--May:-1974 sampling period.
34
Redox potentials measured in subsurface drainage water from ST
DT, and DTL plots during the May, 1974 sampling period.
35
In situ redox potentials of ST, DT, and DTL soils during the
--M~1974 samp1 ing period.
xx
Page
94
96
97
97
101
101
102
103
103
-------
ACKNOWLEDGMENT
This research was performed in conjunction with the Soil-Water-Atmos-
phere-Plant (SWAP) Project. The SWAP project was established in 1968 as
a cooperative research program of the Institute of Food and Agricultural
Sciences (IFAS) of the University of Florida and the Agricultural Research
Service (ARS) of the United States Department of Agriculture. The SWAP
project was organized for the purpose of solving critical problems that
restrict the effective agricultural use of soil, water, atmosphere, and plant
resources in Florida. The experimental citrus grove used in this report was
planted in 1970 as one of the primary research efforts of the SWAP project.
The support of IFAS and ARS were invaluable to the research performed on EPA
Project R800Sl7.
Special recognition is given to the Soil Science Department, the Food
Science Department, the Agricultural Engineering Department, the Agricul-
tural Research Center at Fort Pierce, Florida, and the Agronomy Department
of the University of Florida for the use of their facilities.
Recognition is given to Dr. David S. Brown of EPA's Environmental
Research Laboratory, Athens, Ga. Dr. Brown served as Project Officer during
the first two years of this grant. His assistance and cooperation during
the initial stages of the project are greatly appreciated.
The investigators are also appreciative to Chris Young and Mrs. Ann
Barry for typing this completion report, and to Richard Janka for assistance
in drafting of figures.
xxi
-------
srcTIOI\J I
! 1\11 I\ODUCT I ON
During the past 50 years, improved 5011 water management and increased
uti 1 ization of ferti! izers and pesticides have contributed greatly to incre-
ased production of agi Icultural crops. Increased crop yields per unit land
area are largely responsible for the relatively low costs for food and fiber
commodities currently available to the J\merican consumer. Agricultural
scientists are therefore presently concerned with the development of water
and chemical management of (TOPS v-/hich w,'11 improve production efficiency
for consumer commodities alld silTlu1taneously prevent the contamination of the
soil-water environment with un~esirable concentrations of chemicals from
appl ied fertil izers and pesticides Thus the objectives for agricultural
research are multi fold: to prevent pollution of groundwater and other water
suppl ies. to prevent eutrophication of lakes, to provide efficient utiliza-
tion of irrigation water and ca~tJy fertil izer nutrients by crops, and to
provide effective control of vveed, insect and microbiological pests.
The occurrence of potentially harmful concentrations of agrichemicals
in groundv>Jater, drainage canals, anJ 5tl-eam:::. may be greatest (Nelson, 1972)
in areas where cash crops are gr~~n mainly on sandy soils which receive
frequent appl ications of irrigation water, insecticide, herbicide and fert-
ilizer. Such conditions exist in the humid, subtropical climate of Florida.
Recent investigations indicate that llnder certain crop management practices
the possibil ity exists for substantial leaching losses of ferti 1 izer nutrients
in acid, sandy soils of r10rida (Calvert and Phung, 1971; Calvert, 1975;
Forbes et al., 1974; and Graetz et al., 1974). However, the exact fate of
appl iedferti 1 izer materials vvas-not-shovvn in these studies. Soi 1 manage-
ment practices are needed for crops growing in a humid climate on sandy soils
to prevent or minimize pollution resulting from discharge of agricultural
chemicals through surface and subsurface drainage waters. Basic information,
however, is lacking fOI~ conc.entrations as well as discharge of nutrients and
pesticides in drainage VI/atel" horn individual agricultural fields, and how the
loss of these chemicals is affected by management of soil, water, fertil izer,
and pesticide resources.
A brief seatch of the] iterature readily shows that many factors affect
the loss of pesticides or nutrients such as nitrogen and phosphorus in sur-
face runoff and drainage "vaj~et'5 from subsurFace-drained agricultural soils.
Jury (J975) stated that liThe solute flux or concentration of water collected
at the tile contains contributions from all parts of the field being drained,
in proportions which depend on ti 1e line spacing, soil permeability varia-
tions, and type of infiltration (ponded or unsaturated). This complex super-
position, coupled with a phase delay due to travel time variations from point
to point on the field, greatly obscures the relationship between input and
outputll.
-------
Although soil water is the medium by which solutes such as nitrate are
transported through soil, water and dissolved chemicals do not always move
with the same velocity. Biggar and Corey (1969) state that the movement of
solutes through soil frequently lags behind water movement largely due to
mixing processes such as diffusion and hydrodynamic dispersion which occurs
between the resident soil solution and infiltrating water from irrigation
or rainfall. In addition, ions such as ammonium or phosphate can be further
detAined in their movement in the direction of soil water flow by adsorption-
desorption interaction with soil colloids. Phosphorus in the soil solution
can also undergo precipitation with iron and aluminum and therefore be removed
from the solution phase. Ammonia, of course, is also subject to microbiolog-
ical transformations to form nitrate under aerobic soil conditions, and
nitrate is subject to form N20 and N2 gases under anaerobic conditions. Sol-
uble organic herbicides such as terbacil and 2,4-0 also move through soil at
velocities considerably less than that for water. These herbicides are sub-
ject to adsorption-desorption and microbiological degradation, as well as
many other processes. In general adsorption has been shown to be a better
indicator of potential movement in soil than solubil ity in water (Biggar,
1970). Thus, change in concentrations of fertil izer nutrients and pesticides
in surface runoff and drainage waters is a complex function of time due to
solute dispersion, transport, interactions with the soil, and microbiological
transformations.
The quantity and velocity of water flowing through soils to subsurface
drains are of major importance to the leaching loss of applied fertil izers
and herbicides. Bolton et al. (1970) measured nutrient losses in tile drai.n-
age water for crops growTng-on a clay soil for a 7-year period. They con-
cluded that the total volume of drainage water for a particular cropping sys-
tem was the predominant factor influencing nutrient loss. Discharge of nut-
rients was distinctly greatest during seasons when large amounts of drain
flow occurred. Water uptake by plants (transpiration) tends to decrease the
volume of drainage from the soil. Both Bolton et al. (1970) and Erickson
and Ellis (1971) observed less fluctuation in concentration of a given nut-
rient in drainage water with time during a specific season than for the
fluctuations of discharge flux (product of solute concentration and drainage
water flux) for the nutrient.
Removal of fertil izer nutrients from the mobile soil solution by growing
plants is generally considered to be relatively inefficient. Ayers and
Branson (1973) state that uptake of applied nitrogen is frequently 50% or
less. Recovery of applied phosphate by plants averages about 30% (Nelson,
1975). A large portion of the nitrogen that is not removed by crops is sub-
ject to potential leaching 1055 from the ro?t zo~e. Johnson ~~. !1965)
found that rather large percentages of appl led nitrogen (range: 9-70/0) were
lost in tile drainage effluent from irrigated land in Cal ifornia. Losses
of phosphorus were much less (range: 1-17%).
Frink (1971) states that the efficiency of nitrogen uptake by a crop is
greatly influenced by the rate, the method, and the timing of fertil izer
appl ications. Of these three factors, proper timing of fertil ization appears
the most important. He states that by timing applications of fertilizer to
coincide with maximum demand of the crop, less nitrogen is required to pro-
duce the same crop yield.
2
-------
Generally speaking, concentrations of N03-N are lower in surface runoff
water than in subsurface drainage; whereas, tne concentration of soluble P
is usually higher in runoff water than in drainage (Biggar and Corey, 1969).
The concentration of soluble P is frequently less than 0.01 ~g/ml in the soil
solution of the subsoil horizons of most soils (Biggar and Corey, 1969).
Thus the concentrations of P in subsurface drainage water is normally very
low. However, Bingham ~~. (1971) measured N03-N concentrations as high
as 20 ~g/ml in subsurface drainage water from a large citrus watershed in
Ca 1 i fo rn i a .
Ayers and Branson (1973) observed that nitrate concentrations tend to
be higher in groundwater located beneath sandy soils which are intensely
managed for agricultural use. Also concentrations of N03-N in soi I solution
samples taken from the root zone of soil beneath a citrus grove increased
from 19.3 ~g/ml for low nitrogen fertil ization (150 lbs. N/acre/yr.) to 45.5
~g/ml for high nitrogen fertilization (350 Ibs. N/acre/yr.).
During 1968 an interdisciplinary research team comprised of scientists
employed by the UnivErsity of Florida and the Agricultural Research Service
of the U. S. Department of Agriculture was assembled under the Soil-Water-
Atmosphere-Plant (SWAP) Project (Knipling and Hammond, 1971). The SWAP
project was establ ished for the purpose of developing a research program to
solve pertinent problems associated with soil, water, atmosphere and plant
resources for agricultural production. A field experiment was established
on a 20-hectare area at the Agricultural Research Center, Fort Pierce, Flor-
ida to evaluate the effects of three soil management systems - Shallow
Tillage (ST), Deep Ti llage (DT), and Deep Tillage Plus Lime (DTL) - and two
drainage systems - subsurface drains with Submerged (S) and Open (0) outlets
on soil and water properties, drainage characteristics of the soil, and
growth response of 12 citrus rootstock/scion combinations. Historical back-
ground of the project and a detailed description of the design and objectives
of the SWAP study have been given by Knipl ing and Hammond (1971). Soil with-
in the experimental area are classified as Spodosols (acid flatwood soils)
which represent a major physiographic unit within Florida (Figure 1) and in
the Southeastern United States. The land area shown in Fig. 1 and designated
as Spodosols also includes the order of Alfisols which are sandy soils with
larger contents of colloidal material (clay minerals and organic matter) than
the associated Spodosols. This schematic map provides only a very general
description of the location of large areas of Spodosols in Florida. Compared
to the Spodosols, the Alfisols are generally more fertile soils.
Spodosols and other associated flatwood soils represent the most exten-
sive order (Zelazny and Carl isle, 1971) of Florida soils and account for
approximately 25% of the total land area. Sites ~~. (1964) have stated
that approximately 5 mill ion acres of flatwoods and marshes occur just in
the central and southern sectors of the state. Generally, Spodosols occur
on nearly level to gently sloping landscapes with a shallow groundwater table
which fluctuates near the soil surface during summer and early fall periods
of high rainfall (Brasfield et al. 1973). Spodosol profiles are character-
ized by the presence of a subSurface spodic horizon which is an accumulation
of organic matter with varying amounts of aluminum and iron. The spodic
horizon usually (Brasfield ~~. 1973) has relatively high levels of catior.
3
-------
exchange capacity, specific surface area, !,'\Iater retention capacity, and
exchangeable acidity. This horizon Gommonly occurs at depths less than 75
cm beneath the soil surface and is over]ai,l by salld; A2 eluvial and Al sur-
face horizons. Spodosols are typically strongly acid sandy soils which have
low levels of fertility and base saturati !Ilternal drainage of these soils
is generally I imited by the presence of the spodic horizon which is slowly
permeable to water. However, if r"c:r,::']lc1 su!:J::,\JI-Pa,-:;\,;; drains are placed in
these soils, lateral drainage through the AZ horizon can be rapid, particu-
larly where the spacing between drains is sma] 1.
During 1973 the Environmentd] Proteccion Agr:::ncy funded Grant #R800517
to investigate the influence of applied fenilizl~' and pesticides upon the
water qua 1 i ty of su rface runoff and sUb",Uir,=j(":; drC\ i nage \Alaters in the SWAP
citrus grove. The objectives of that proi,sct \j\lei~,':' ae: fol1o\i'ls: (I) to deter-
mine the movement and fate of N03-N. PGb-P terbacil, 2,4-dichlorophenoxy-
acetic acid. and chlorobenziilate th;-ough r:!v soil ,ofile and into drainage
water from a citrus grove9 (2) t'~1 eVdL'2i~c th,,=: ir,,'il,''':(ice of the three soil
management systems - Shal Jaw 1i1 lage (51). Deep Tillage (DT) and Deep Tillage
plus Lime (DTL) "and the t\'\IO dr~';na'~::o "",:': ilS ~> ;j::jl-w=rged (S) and Open (0)
drain outlets - upon the concentratir)1l "Hid fliL( of selected agrichemicals in
surface runoff and subsurface draina9'''' \I\/ai:;c,-:;, ,:::,"1':1 (3) to determine base-
level concentrations of selected agrichelTIlcaL. II! subslHface drained soil
which has sad vegetation and that has 1-2' eived n:) .3!JrJl ications of fertil izer
and pesticides.
~=~~=' 1'-'
'=-'''=~=~=-" !" ~! -, -i'~', If
~y,<- ~l\ III""" 1'1
~" -., ''.l;!/,_.,IJ.,tl,
, j
'~l
Spodosols (n~
~~L>
:
, 1\)
II,t
I'
II'.
1",
ii" 'Ie: ;-~; I,~ t
1/11\)\ - I <
<-J~
J
Pierce
FIGURE I.
t1ap of Florida Shr)Hing 10':ations of l1lajor' an:;as of Spodosols.
,I
-------
SECTION I I
CONCLUSIONS
Acid, sandy Spodosol soils of Florida are typically poorly drained. The
presence of subsurface spodic and clay strata in the profile impede water
flow vertically from the profile and enhance lateral flow along the top of
the spodic layer. Nearly flat topography also 1 imits rates of surface and
lateral subsurface drainage. During periods (summer) of frequent rainfall
a water table develops in the soil profile and sometimes inundat~s the soil
surface. Agricultural development of flatwood land thus normally includes
establishment of ditch or subsurface drainage systems for the purpose of
removing excess soil water and maintaining a water-unsaturated root zone in
the upper portion of the soil profile for optimum plant growth. Citrus
trees are grown on these soils using slightly elevated beds to provide sur-
face drainage and either open ditches or buried tiles to provide subsurface
drainage.
Both the nutrient and water retention capacities for the sandy surface
horizons of Spodosols are characteristically small. Consequently, agricul-
tural management of citrus growing on flatwood soils usually includes quar-
terly applications of fertil izer and appl ications of irrigation water as
needed during periods (winter and spring) of infrequent rainfall. In addi-
tion to fertil izer, other chemicals such as herbicides, insecticides, fungi-
cides, and acaricides are appl ied to control specific pests.
Agricultural chemicals such as fertilizers and pesticides appl ied to
citrus groves on drained flatwood soils are occasionally suspect as potential
contaminants of groundwater and drainage canals. Primary objectives for this
research project were first to quantitatively assess the water pollution
potential of two fertil izers--nitrogen and phosphorus--and three pesticides--
terbacil, 2,4-0, and chlorobenzilate--when appl ied during routine management
of a subsurface-drained citrus grove located on a Spodosol and second to
evaluate the influence of three soil management schemes--shallow tillage (ST),
deep tillage (DT). and deep tillage plus lime (DTL)--upon the water pollution
potential of these chemicals. An unfertilized Control plot with subsurface
drainage but without citrus trees was also establ ished. Volumetric discharge
rates and chemical analyses of surface runoff and subsurface-drainage waters
were measured with time. Water flux and chemical concentrations were inte-
grated to determine discharge of the 5 applied agricultural chemicals with
surface and subsurface drainage.
Based upon results obtained from this research, the following conclu-
sions were made:
(I) Following periods of rainfall or irrigation, flux and accumulative dis-
charge of subsurface drainage were consistently greater from the shallow-
tilled treatment, ST, relative to that for the deep-tilled treatments, DT
5
-------
and DTL. Drainage flux and accumulative discharge from the soil management
treatments were in the order: ST» DT > DTL ~ Control. Average monthly
amounts of drainage from ST were approximately twice that for DT.
Average annual quantities of subsurface drainage for the three-year per-
iod 1973-75 were 78, 43, and 27 cm, respectively for ST, DT, and DTL plots.
The average annual sum of rainfall and irrigation for the same period was 155
cm. Thus drainage water from the ST plot was equivalent to 50% of the total
water input from rainfall and irrigation. For DT and DTL plots drainage
water represented only 28 and 17%, respectively of total water input. This
observation indicates that the slower drainage in the deep tilled treatments
provided opportunity for storage of infiltrated water over longer periods of
time than for the shallow-tilled plot. Thus deep tillage tended to increase
the length of time for water storage in the soil profile following rainfall
or irrigation. In fact estimated values of evapotranspiration for the
three treatments were in the order ST « DT < DTL.
Drawdown of the water table in the soil at the midplane between parallel
subsurface drains was in the order ST» DT > DTL. During a ten-day period
following an irrigation of 16 cm of water, approximately 1.4, 3.0, and 6.2
days were required for the water table to move from near the soil surface
to a depth of 60 cm for ST, DT, and DTL plots. Although the very rapid
drawdown of the water table in the ST plot provides for rapid establ ishment
of aeration in the rooting zone, the accompanying rapid movement of soil
water also increases the potential for greater loss of applied fertil izer
nutrients.
Overall growth of citrus trees and fruit yields for the three treatments
were in the order ST « DT < DTL and ST ~ DT « DTL, respectively. The deep
tillage treatment thus improved growth and yields from citrus, probably due
to increased capacities for temporary storage of water and nutrients in the
root zone of the soil profile.
(2) Greatest leaching losses with subsurface drainage from the soil profile
for both N03-N and P04-P occurred from the ST treatment. Concentrations of
P04-P appearing in the drainage water from the ST plot were higher than
expected. Both DT and DTL plots leached very small amounts of P04-P com-
pared to that for an unfertil ized Control plot apparently due to the greater
surface area and chemical nature for retention of P04-P provided by the
colloidal organic and inorganic materials which were incorporated into the
otherwise sandy profile by the deep tillage. The DTL treatment gave signi-
ficantly more N03-N discharge into the drains than the DT treatment and was
probably due to the higher nitrification rate found for the DTL soil.
Average annual losses of N03-N in surface and subsurface drainage from
ST, DT, and DTL plots were equivalent to 22.2, 3.1, and 5.4% of total N
applied as fertil izer. Thus deep tillage decreased N03-N loss by approximately
fourfold over shallow tillage. Loss of N03-N from the combined treatments of
deep tillage plus 1 ime was also greater than for the single treatment of
deep tillage.
Average annual losses of P04-P in surface and subsurface drainage from
6
-------
ST, DT, and DTL plots were equivalent to 16.9, 3.6, and 3.5% of total P
applied as fertilizer. Thus deep tillage decreased P loss by more than four-
fold over shallow tillage. Essentially no differences were observed in P
loss from DT and DTL plots. Annual losses of both Nand P were relatively
high for the ST plot.
The ratios of N03-N and P discharged in subsurface drainage from all
three soil plots were greater than the ratio of 9.2 for Nand PappI ied as
fertil izer. For ST and DT the N-to-P ratios were 12.1 and 10.5, respectively. How.
ever, the N-to-P ratio in drainage from DTL was 20.3 or almost twice that for
either ST or DT. The large N-to-P ratio for DTL reflects the smaller leach-
ing loss of P and the larger leaching loss of N relative to that for DT. For
the nutrient content of oranges the average ratio of N-to-P is 8.0 which is
slightly less than the ratio of 9.2 for the fertilizer.
(3) Timing of fertilization with respect to rainfall or irrigation events
was observed to greatly influence leaching loss and thus nutrient enrichment
of subsurface drainage water. Losses of N03-N in drainage from ST soil were
relatively large and depended upon the quantity of water appl ied when irri-
gation immediately followed application of fertil izer. During 14-day periods
following 16.0, 8.2, and 2.4 - cm irrigations N03-N losses represented 34,13,
and 2% of N applied in the fertilizer for ST. Discharges of N03-N from
DT after 16.0, 8.2, and 2.4 - cm irrigations were only 1.34, 1.06, and 0.02%.
However, comparable losses from DTL were 12, 8, and 0.2%, respectively.
Losses of P04-P in drainage after the 16.0, 8.2, and 2.4 - cm irrigations
were 8, 3, and 0.9% for ST; 1.56, 0.14, and <0.01% for DT; and 2.31, 0.12,
and <0.01% for DTL.
(4) Potential leaching losses of applied Nand P for citrus growing on tile-
drained Spodosol was observed to be greatest during the six-month period
from May through October. During these periods for 1973 1975 approximately
78% of annual rainfall occurred. During these high-rainfall months N03-N
discharged with subsurface drainage accounted for 78% of the total annual
loss of N03-N from ST, 83% for DT, and 74% for DTL. Losses of P04-P account-
ed for 90, 89, and 88%, respectively of total annual quantities discharged
from ST, DT, and DTL.
(5) Application of fertilizer was observed to increase the concentrations of
N03-N and P04-P in drainage water from ST, DT, and DTL plots. However, as
the drainage water moved through a long perimeter ditch to the South Sump
the concentrations of nutrients were greatly decreased. Nutrient concentra-
tions in drainage water sampled from the surrounding perimeter ditch and
from the non-tilled, unfertilized Control plot and in the South Sump for the
entire SWAP citrus grove were generally much lower than that found in the
drainage water from the tilled and cropped areas. The lower concentration
of P in the ditch and South Sump can probably be explained by fixation of P
with clay minerals in the ditch banks and by uptake by plants in and near
the water. A dilution effect also was caused by water coming from unferti-
lized areas. N03-N probably was absorbed by plants and underwent denitrifi-
cation in the anaerobic conditions of the ditch bottom.
(6)
Losses of N03-N and P04-P with surface runoff were very small for all
7
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treatments. Runoff rarely occurred from ST and occurred from the deep-tilled
plots only during intense rainfall or irrigation of long duration. Runoff
occurred after the soil profile had become water-saturated.
(7) Denitrificationcan be a significantly large sink for nitrogen appl ied
as fertil izer to the DT and DTL treatments. The relatively slow drainage
characteristics of these deep-tilled soils in conjunction with the capacity
of the soil located in the lower portion of the profiles to denitrify nitrate-
N contribute to this sink. In the ST or shallow-tilled soil denitrification
takes place only in the surface or Al horizon. Since the soil in the Al
horizon is seldom water-saturated under conditions of subsurface drainage,
considerably less denitrification is 1 ikely to occur in the ST soil relative
to that in the DT and DTL soils. Rate coefficients for denitrification were
found to be (average for three soil depths) 2.24, 0.44, and 0.88 10-3/hr for
ST, DT, and DTL soil. Thus the DTL soil has a greater potential for denitri-
fying N03-N than does DT soil.
(8) Although deep tillage clearly decreased nutrient (mainly p) leaching
losses from the soil its affect upon pesticide loss was not as dramatic.
Discharge measurements in drainage indicated some movement of terbacil and
2,4-D herbicides but essentially nil loss of chlorobenzilate. The results
with chlorobenzilate were expected since it is not a water-soluble material
and it was applied directly to the citrus foliage. Losses of terbacil and
2,4-D in subsurface drainage of DT and DTL plots was, however, less than that
for ST. Total discharges of these two herbicides were in the order ST >
DTL > DT.
Discharge of herbicide with subsurface drainage was affected by the type
of drain outlet. For 2,4-D, leaching loss was greater from drains with open
outlets than from drains with submerged outlets. Loss of terbacil in drain-
age, however, was not greatly different for open and submerged drains. Since
the half-life of 2,4-D is approximately one tenth of that for terbacil, the
higher water content and poorer aeration in soil above submerged drains is
believed to have influenced microbial degradation of 2,4-D more so than for
terbac i 1 .
(9) Changes in concentration of N03-N in subsurface drainage from DTL soil
was observed to follow changes in concentration of soil solution surrounding
the drain tube. However, N03-N concentrations in portions of the upper 60
cm of soil were as high as 120 wg/ml in the soil solution even when the con-
centration in drainage water was less than 8 wg/ml.
(10) A mathematical model was developed to describe the simultaneous trans-
port of P and water through soil. Kinetic theory was used to incorporate
reversible transformations of P between dissolved, adsorbed, immobilized,
and precipitated phases.
8
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I.
SECTION I i I
RECOMMENDATIONS
The 'following management guidelines are recommended to citrus grove
ope~ators and other land management special ists for controlling pollu-
tion from non-point sources of fertilizer and pesticide in citrus groves
located on Spodosols:
A.
Excessive rates of fertilizer and herbicide application are wasteful
and contribute to unnecessary pollution of our waterways. Rates and
timing of chemical appl ications should coincide with citrus demand
for nutrients and should be consistent with soil water management
(irrigation, rainfall, drainage, etc.). Fertilizer applications
should be minimized during Florida's summer rainy season to avoid
excessive leaching of nutrients from fertil ized soil. Most efficient
usage or uptake by plant roots of applied fertilizer occurs when the
use-efficiency of infiltrated rainfall and irrigation is also large.
B.
Although expensive, deep-tillage appears to be a practical management
method for flatwood soils (Spodosols). If horizons of fine textured
material exists in the subsoil, colloidal materials can be incorpo-
rated into the otherwise coarse sandy surface soil and thereby reduce
leaching of appl ied agrichemicals.
C.
Collecting the drainage water from citrus groves in reservoirs for
recycling through irrigation systems could permit recovery of some
of the discharged nutrients and increase the water use-efficiency
during periods of 1 imited rainfall.
D.
Although the deep tillage treatment was observed to
losses of appl ied nutrients and herbicides, initial
lishment of deep tillage by the trenching method is
$18,664 per hectare which is prohibitive for use by
rus growers. Several options are available however
the deep tillage treatment at much less cost.
decrease leaching
costs for estab-
currently about
commercial cit-
for utilizing
One alternative is to use the trenching method to deep-till a 45-cm
swath along the rows of citrus trees. Estimated cost for selec-
tive deep tillage would be only $1,023 per hectare. Growing citrus
trees under those conditions would be somewhat 1 ike growing the
trees in large pots since leaching loss of nutrients and water
could be greatly decreased in the deep-tilled soil adjacent to the
tree rows. Appl ications of fertilizer would be restricted to the
surface soil of the deep-tilled swath. More efficient water use
could also be provided by applying irrigation water directly to
the base of the trees using the drip/trickle method.
9
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Shallow placement of smaller drains with narrower spacing could also
be used as an alternative to the deep placement of large drains with
wide spacing as currently used at the SWAP citrus grove. Recent
work by Fausey (1975) indicates that shal low subsurface drains can
be used to control seasonal high water tables in soils with an imper''''''''''''''
meable or slowly permeable layer at a shallow depth. Relatively
small diameter corrugated plastic draintubes can be installed at
shallow depths (Fausey, 1975) by the "plow-in" method for consider-
able cost savings over conventional trenching methods for installihg
deep drains. Fausey (1975) used a finite difference model to
simulate transient water flow to drains in a two-layer soil where
the depth to the impermeable lower boundary was 150 cm and the layer
interface was 55 cm from the ground surface. He concluded that if
the hydraulic conductivity for soil in the top layer was 5 times or
more greater than that for the bottom layer, the rate of midplane
recession of the water table during early stages of drawdown was
greatest when the drain was placed at 50 cm depth. Fausey (1975)
concluded that shallow drainage of layered soils appears to be
feasible.
Another alternative means for establishing deep tillage over the
entire soil area at a greatly reduced cost over the trenching method
is to use a moldboard plow. Kaddah (1976) stated that deep tillage
of a soil profile could be accompl ished to a depth of 120 cm by
moldboard plowing for a cost of $148-198 per hectare. The cost is
further increased, however, by cost for land level ing which is
required after deep moldboard plowing.
Estimated current costs for initial establishment of a pop-up sprin-
kler irrigation system and subsurface plastic drain tubes are $2,471
and $2,242 per hectare, respectively for either shallow-tilled or
deep-tilled plots.
2.
The following future research studies are suggested for
tional insight into the effects of routine appl ications
and herbicide upon the qual ity of groundwater and water
providing addi-
of fertilizer
in canals:
A.
To assess the amount of nutrient and pesticide movement under the
common (in Florida) grove drainage situation of surface and subsur-
face drainage by widely spaced ditches, samples should be collecLed
during peak periods from ground water draining from groves planted
on Spodosols and otherwise developed similarly to ST treatment
except with ditch spacing greater than the relatively narrower
drain spacing used in this study.
B.
The effectiveness of removing nutrients and pesticides from drain-
age water by storage and recycling from reservoirs should be
assessed in a study conducted at the SWAP citrus grove.
c.
To more precisely identify the source of nitrates found in the
drainage water and determine paths for movement of N in subsurface-
drained soil a study, using 15N03-N or similar tracer should
10
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be conducted.
D.
Maximum discharges of nutrients and pesticides should continue to
be determined on a long-term basis, particularly for years when the
total rainfall exceeds the average. In the present long-term study
the total rainfall amounts were average or below.
E.
To make best use of current data presented in this report, a mathe-
matical model should be developed to simulate two-dimensional trans-
port of water and agrichemicals (N03-N, NH4-N, P, K, and terbacil)
during non-steady water infiltration and drainage of a fertil ized
Spodosol resulting from irrigation or rainfall events. Such a
model should also describe interactions such as adsorption-desorp-
tion, chemical precipitation, fixation, denitrification, and nitri-
fication. Experimental measurements of water content and solute
concentration in soil surrounding a subsurface drain are also needed
to validate results from such a model. Concentrations of agrichemi-
cals in the drainage water should be compared with concentration
distributions in the soil solution.
11
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SECTION IV
CONCENTRATION AND FLUX OF N03-N AND P04-P IN SURFACE AND SUBSURFACE
DRAINAGE WATER FROM A FERTILIZED CITRUS GROVE
EXPERIMENTAL METHODS AND PROCEDURE
Field Procedures
A schematic diagram of the entire SWAP experimental field site is shown
in Figure 2. A single replicate each of the ST, DT, and DTL soil management
treatments were selected from the northwest corner of the site for the pur-
poses of performing research on EPA Grant #R8005l7. The primary soil type
in the selected area of study was Oldsmar sand, a member of the sandy sili-
ceous, hyperthermic family of Alfic Arsenic Haplaquods (Spodosol). The dark
spodic horizon ranged in depth from 86 to 107 cm with an average of 96 cm in
undisturbed profiles; this spodic horizon (many Spodosols do not have such
sandy clay material beneath the spodic horizon) was underlain by layers of
fine sandy clay. The AI, A2, and A22 horizons of acid sand had a total aver-
age depth of 82 cm and the organic content was 2.30% in the surface AI-horizon
soil (Table I) but decreased with depth. These sandy horizons are highly
permeable to water flow and are underlain by 10 to 20 cm of a nearly imper-
permeable (saturated hydraulic conductivity of 0.02 cm/hr) spodic layer con-
taining 3.56 percent organic matter (Table 1). The spodic layer is under-
lain mostly by sandy clay loam which like the spodlc layer has a low satu-
rated hydraul ic conductivity (0.12 cm/hr) and is thus also slowly permeable
to water flow.
Main plot treatments in the entire SWAP field experiment consisted of
three profile modifications. . Each plot (Fig. 3) contained 3 open-outlet
drains and 3 submerged-outlet drains and was approximately 1 ha in area (91.4
by 109.7 m). Treatments were repl icated three times. Soil modification
treatments were as follows: (i) Shallow-Tilled (ST) to 15 cm depth and nor-
mal surface liming with dolomitic limestone (2.24 metric tons ha-l year-I);
(ii) Deep-Tilled (DT) to 105 cm depth by a trenching machine and with the
same liming as the ST treatment; and (iii) an initial appl ication of 56
metric tons ha-I dolomitic limestone subsequently incorporated by deep-til-
lage (DTL) of the soil to a depth of 105 cm. All of the limestone contained
approximately 60% agricultural grade dolomite (40% coarse grade dolomite).
Surface drainage was provided in ST, DT, and DTL plots by establ ishing 38 cm
(height of bed crown above bottom of water furrow) high and 15.2 m wide
(measured from centers of water furrows) beds sparated by parallel water
furrows. Swale ditches establ ished at each end of the water furrows and per-
pendicular to the furrows provided removal of surface drainage water from the
experimental plots. Two citrus rows 7.6 cm apart and with a spacing of 4.6 m
between trees in each row were establ ished along the top of each bed. Sub-
surface drainage was provided by 10-cm corrugated plastic tubing placed at
an average depth of J07 cm and spacerl lR.3 m apart. Surface drainage by
12
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FIGURE 2.
J-I 0 I(J)
01 L I
J-I +-'
Z-- I c I
U)I I 0 I
I en 0 U
en I 0
I J-I
Lf) J-I 0 (f) ...J! U)I
I I
01 J-I J-I 0 I en
I I'- 01
0 I (\J (f) OJ 0 0 I en en 0
(f) "" I 0 0 1 (V) (f) ...JI
J-I
~ I ...JI 01
1-, J-I
(/)1 01 «)
Sampling Sites
l.
2.
3.
4.
5.
6.
7.
8.
9.
Surface tilled submerged drain
Deep tilled submerged drain
Deep tilled 1 imed submerged drain
Surface tilled surface runoff
Deep tilled surface runoff
Deep tilled limed surface runoff
Center Sump
South Sump
Control drain
Schematic diagram of the SWAP field experiment located at the
Agricultural Research Center, Florida Agricultural Experiment
Station, Fort Pierce, Florida. Locations for nine sampling sites
are shown.
13
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TabJe 1. Selected physical and chemical properties of representative ~
sam led from Oldsmar sand at the SWAP citrus rove near Fort
So i 1 Organic Bulk
Profi Ie Horizon Depth Sand S i 1 t Clay Matter2 Dens i ty I
cm -------%-------- gm/cm3)
ST Al 2-8 96.2 2.6 1.2 2.30 1.03 1.28
ST A21 18-23 98.3 0.7 1.0 0.62 0.70 1. 55
ST A22 50-56 97.9 1.0 1.1 0.09 0.49 1.64
.l:- ST B2h 86-91 88.6 3.3 8. 1 3.56 1. 18 1. 75
ST B21 107-112 88.1 0.4 11.5 0.26 4.25 1. 62
ST B'22tg 130-135 76.1 1.0 22.9 0.18 4.32 1. 68
ST B23tg 188-194 1. 78
DT Mixed 0-50 4-62 1. 21 1. 57 1. 61
DTL Mixed 0-50 ---- --- 4-62 1. 21 3.32 1. 61
1 Da ta from Hammond, Ca r 1 is 1 e and Rogers (1971).
2Data from F i s ke 1 I and Ca 1 vert (1975).
-------
I~
91.4 m
N
j
"'
I, ,I I ' I' I .
I I I I I
I I I I I
I I I I I
I I I I I
I I I I I
, I I I I I
I I I I I
I I I I I
I I I I I
I I I I I
,7m I I I I I
I I I I I
I I I .1 I
I I I I I
I I I , I
I I I I I
I I I I I
t , I I I I
18.3 I I I I ,
m I I I I ,
L I I I I I
I' , I , ".-~.
i. 'I' . I . I I: t-~'
1-15.~ BED '-/7.61-
OPEN
DRAIN
109
SUB-
MERGED
DRAIN
6m
m
WATER / m
FURROW
: 3.
Schematic diagram of a single main plot showing split plots
(submerged and open drains). Dots indicate the location of
citrus trees on beds.
15
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raised, multiple-row beds and subsurface drainage by either tile drains or
open ditches are commonly re.comrT]ended (Sites et al., 1964)forr 'citrus growing
on flatwood and marsh soils of Florida. In general the water table in such
soils should not be allowed to rise closer than 60 cm from the soil surface.
In the DT and DTL treatments deep tillage removed soil material high in
colloidal (clay minerals and organic matter) content from the subsurface
spodic (B2h) and sandy clay horizons (B2l and B22tg) and mixed this material
with the sandy AI, A2l, and A22 horizons. Thus the DT and DTL soil profiles
contained higher contents of clay minerals and organic matter (Table 1) in
the top 50 cm than were present in the same depths of the ST soil profile.
In the surface soil the cation exchange capacity (Table 1) was higher for
DT (1.57 me/100g) than for ST (1.03 me/100g) and approximately twice as high
in DTL (3.32 me/100g) than in DT.
Three plots in the northwest corner of the SWAP citrus grove which rep-
resent each of the three soil treatments were chosen (Figure 2) as sites for
monitoring the water quality of surface and subsurface drainage waters. Only
the center drains with submerged outlets for each plot were monitored. Water
from both surface runoff (sampling sites 4, 5, and 6) and subsurface drains
(sampling site 1, 2 and 3) were sampled in each of these three plots. In
addition, water quality was monitored at three other locations (sampl ing
sites 7, 8 and 9) indicated in Figure 2. These locations were the Central
Sump, which collects water,.9<\,tf..1p.ws from all subsurface.:dra.ins, the South
Sump, which collects water from the large perimeter ditch which encompasses
the entire citrus grove, and a check or Control drain, respectively. A dia-
gram of an individual main plot in the Soil-Water-Atmosphere-Plant (SWAP)
project is shown in Figure 3. The surface drainage system consisted of
shallow water furrows (north-south direction) between two-row beds of citrus
trees perpendicular to the subsurface drains. Individual surface runoffs
from each main plot were fed through H-flumes and culvert inlets to the field
ditches to provide measurement of surface runoff from each block. A peri-
meter field ditch was constructed to encompass the entire SWAP experimental
area, and the Central Sump G:onnects to the perimeter ditch .by means of two
lateral service ditches which extend 122 m from the east and west sides of
the area (Figure 2). The perimeter ditch was constructed with a bottom
width of 1.2 m, a one-to-one side slope, and at an average depth of 1.6 m
below ground surface with a 0.02 percent grade. During periods of frequent
rainfall, this ditch carries the composite of both surface and subsurface
runoff to the collection sump (sampl ingsite 8) for pump discharge from the
area and serves during periods of infrequent rainfall as a reservoir for
irrigation water. The discharge pump located at the South Sump has a 26.5
m3 per minute capacity for rapid water removal from the perimeter ditch.
A Control plot with subsurface drains was established in August, 1973,
on land adjacent to the SWAP citrus grove (Figure 2; sampling site 9) and
was maintained in natural sod cover which was mowed occasionally. Three
subsurface drains each 100.6 m long were placed at 107 cm depth and spaced
18.3 m apart. This control plot was not planted to citrus, received no til-
lage, and received no application of agricultural chemicals. For ST, DT,
DTL, and Control plots, calibrated weirs located at the outflow of each cen-
ter drain were used to continuously monitor the volumetric discharge of
16
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water with time on a strip-chart recorder. One hundred ml samples of the
outflow water from the center drain of the Control plot were collected weekly
for both pesticide and nutrient analyses during times of flow and more fre-
quently during periods selected for intensive sampling. Since the Control
plot was not irrigated, sampling of this area was largely confined to periods
with significant rainfall. Water table wells established midway between the
drains in both treated (ST, DT and DTL) and untreated (Control) areas per-
mitted observation and strip-chart recording of the water table depth. For
ST, DT, and DTL plots (but not for the Control), surface runoff flumes were
also constructed. During periods of surface runoff the height of water dis-
charging through the flume was measured continuously with a strip-chart
recorder and water samples were also taken for nutrient and pesticide analy-
ses. A single bulk water sample was obtained from each location for each
runoff event. A small pump was operated at a constant flow rate during run-
off-and this was collected in a 10-liter glass carboy.
The subsurface drains, shown in Figure 3, consisted of continuous leng~hs
of perforated corrugated plastic tubing (10 cm inside diameter) 91.4 m long
and spaced 18.3 m apart with a 0.17 percent slope (on each line). Each drain
was placed in the soil tv a depth of 107 cm below average ground surface at
the midpoint along the drain. The bottom half of each drain line was placed
on a 10 cm thick envelope of silica gravel and the top half was covered with
a 23 cm wide linear strip of polyethylene sheet used to prevent sediment from
entering the drain. Water from each drain discharged into a concrete manhole
where flow was measured with 12-inch, 30-degree, V-notch weirs and water-stage
recorders, and water samples were collected for later analyses (sampling site
7). Water from all of the 54 drains of the citrus grove is conveyed through
a 20.3 m diameter drain to the Central Sump where it is discharged by a pump
into the lateral and perimeter field ditch drainage system.
During periods of low rainfall and at the beginning of periods selected
for intensive monitoring of drainage water quality, irrigations were applied
uniformly to ST, DT and DTL plots with full circle, rotary, pop-up sprinklers
spaced 9.1 x 15.2 m with one sprinkler centrally located between every four
trees in the middle of the two row bed. The irrigation rate was 0.41 cm/hr
with a line pressure of 25 kg/cm2. The sprinkler nozzles were permanently
mounted flush with the ground surface and rose up 16.5 cm when discharging
under pressure. Since periodic extremes of low and high rainfall are experi-
enced on flatwood soils planted to citrus, soil water management should (Sites
~. ~., 1964) include a combination of drainage and sprinkler irrigation.
Fertilizer was applied as normally recommended for citrus growing on
flatwood soils. Four quarterly applications were made each year during 1973,
1974, and 1975 at a rate and ratio indicated in Table 2. Total annual quan-
tities of Nand P applied were 169.52 and 18.48 kg/ha, respectively.
Precipitation, surface runoff, and subsurface drainage were continuously
measured during the three-year study period. Detailed hydrologic data during
the 3-year period are included in this report as supporting information for
short-term (intensive monitoring periods following applications of chemicals
and water) and long-term studies. Samples of drainage water for chemical
determination of N03-N and P04-P were taken at weekly intervals during July,
17
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Table 2. Fertil izer N, P, K and M9 applied per hectare
to ST, Dr and DTL treatments at the SWAP
citrus grove near Fort Pierce.
Quantity of Fertil izer Appl ied* (kg/ha)
Date N P K Mg
Year: 1973
Ma rch 6 42.38 4.62 35.18 6.36
May 15 42.38 4.62 35.18 6.36
August 21 42.38 4.62 35.18 6.36
October 30 42.38 4.62 35.18 6.36
Annual Total 169.52 18.48 140.72 25.44
Year: 1974
Ma rch 14 42.38 4.62 35.18 6.36
May 21 42.38 4.62 35.18 6.36
September 26 42.38 4.62 35.18 6.36
November 14 42.38 4.62 35.18 6.36
Annual Total 169.52 18.48 140.72 25.44
Year: 1975
March 10 42.38 4.62 35.18 6.36
June 10 42.38 4.62 35.18 6.36
September 5 42.38 4.62 35.18 6.36
November 4 42.38 4.62 35.18 6.36
Annual Total 169.72 18.48 140.72 25.44
Total Appl ication 508.56 55.44 422.16 76.32
*Each appl ication was 530 kg/ha of an 8-2-8-2 commercial
fertil izer (8% ~I, 2% P205, 8% K20 and 2% MgO) which con-
tained ammonium nitrate, diammonium phosphate, potassium
chloride and magnesium oxide.
1973 until January, 1976, during periods of flow from the South and Central
sumps and from the unfertil ized Control _plot were taken concurrently to mon-
itor the N03-N and P04-P leaching losses from these sources. Additionally,
five intensively - sampled periods were employed in conjunction with irriga-
tions scheduled immediately following grove fertilization. The average
length of these periods was 14 days. These intensively sampled periods of
water quality study were conducted in March of 1973, May of 1974, February
of 1975, March of 1975, and June of 1975.
Water samples were collected with ISCO Model 1391 samplers from subsur-
face drains and from the Control plot. During the first five days of inten-
sively sampled periods, sampl ing intervals as small as 2 hours were chosen
18
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for the collection of samples. Samples for routine monthly assessment of
nutrient levels were collected manually from the drains usually on a weekly
basis. However, even during these long-term studies, samples were taken at
daily or biweekly intervals during periods immediately following fertil iza-
tions and during peak flow periods initiated either by rainfall or by irri-
gation.
Laboratory Procedures
After collection, samples were divided and frozen for later delivery to
the University of Florida Pesticide Research Laboratory in Gainesville for
pesticide analyses. Samples to be analyzed for N03-N and P04-P concentra-
tions were u9ually analyzed soon after collection in the field; however,
immediate analysis was not always possible. In that case, three drops of
chloroform were added to each 100 ml sample as a preservative and the samples
were then frozen and stored in a freezer.
N03-N and P04-P analyses were performed with a Technicon Autoanalyzer I I
system using two single-channel colorimeters with a recorder. Nitrates were
determined using the cadmium reduction procedure (Technicon Industrial Meth-
od No. 100-70W). Ortho-phosphate was determined using the ascorbic acid pro-
cedure (Technicon Industrial Method No. 94-70W).
Monthly means of water flow and nutrient movement were calculated to
determine the long-term trends. While actual data points were shown for the
intensive studies, total discharges for water and nutrients were determined
graphically by measuring the area beneath each curve of discharge flux.
RESULTS AND DISCUSSION
Long Term Investigation
Rainfall was recorded daily at the SWAP citrus grove near Fort Pierce,
Florida for 1973 (Table 3), 1974 (Table 4), and 1975 (Table 5). Total rain-
fall amounts for 1973, 1974, and 1975 were 134.6, 124.9, and 116.4 cm. Total
irrigation amounts were 20.6, 38.7, and 29.7 cm for 1973, 1974, and 1975,
respectively (Table 6). Thus the total quantities of irrigation plus rain-
fall were 155.2, 163.5 and 146.0 cm for 1973, 1974, and 1975, respectively.
The six-month periods from May through October was consistently character-
ized by disproportionately large amounts of rainfall. The total rainfall
occurring during these six-month periods represented 79, 82, and 74% of the
total rainfall occurring during 1973,1974, and 1975. Distributions of daily
rainfall, however, were very nonuniform for each of the years.
Mean monthly discharges of water, N03-N, and P04-P with subsurface drain-
age from ST, DT, and DTL plots are oresented in Tables 6-8 and are plotted
with time in Figs. 4, 5, and 6 for 1973, 1974, and 1975. Monthly water dis-
charged from the ST treatment was consistently larger than from the deep-
tilled plots. During 1973 monthly water discharged from the DT treatment
was considerably larger than from DTL; however, during 1974 and 1975, sub-
surface drainage from the DT plot was only sl ightly greater than from DTL.
The decreased water discharged from the deep-tillage treatments relative
19
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Tnble 3. R.ainfall recorded daily at the S\>/AP citrus s>rove near Fort Pierce, Florida
during 1973.
Date
Jan. Feb. Mar. Apr. May June JUly Aug. Se . Oct. Nov. Dec.
1973 Rainfall em
1 0.05 0.23 0.97
2 0.58 0.08 1.80
3 0.86 0.10 1.55
4 1.57 2.67 0.05 0.69
5 0.76 3.61 0.64 0.03
6 0.61 1.17 0.23
7 4.57 0.03
8 3.43 0.71 0.23 1.93 1.17
9 2.29 1.91 2.46 1.73 0.61 1.24
10 0.38 0.43 0.10 0.84 0.03 1.78 0.38
11 1.83 2.44 0.03 0.41
tV 12 0.41 0.10 0.15
0 13 0.03 1.73 0.08 0.05
14 0.03 0.10 2.41
15 0.15 0.81 4.24 0.51
16 1.98
17 0.33 1.65 0.56 1.04
18 0.66 1.57 2.03 0.71
19 0.08 2.62 1.0'7 4.85 0.13
20 0.05 0.86 0.69 4.65
21 0.38 1.27 1.52 0.33 0.61
22 1.14 0.30 1.52 2.06 1.60
23 1.19 1.04 1.04 3.99 0.10
24 1. 0'7 0.86 0.30 1.27 0.94
25 2.72 5.26 2.54 0.66
26 0.48 0.20
27 0.74 1.40 1.09
28 0.64 3.18 0.05 0.08 0.28
29 0.79 1.91 0.28 0.13
30 1.85 1.78
31 0.51
T
-------
Table 4.
Rainfall recorded daily at the SWAP citrus grove near Fort Pierce, Florida
during 1974.
Date
Jan. Feb. Mar. Apr. Oct. Nov. Dec.
1 0.36 0.46 0.28 0.64
2 1.91 0.64 3.51 0.56 0.94 0.30
3 2.03 0.89 0.03 3.48
4 0.56 0.13
5 0.25 1.91 0.56 3.56 2.~
6 0.38 1.63 0.97 1.04
7 0.10 0.05 4.39
8 0.03 3.07 0.08 0.10
9 0.08 0.79
10 3.81
11 1.57 0.28 0.36
N 12 1.91
13 1.14 1.47
14 5.56 0.38 0.56 0.13
15 0.13 2.03 5.59 2.72
16 0.89 6.91 0.91 1.68
17 1.47 0.10 2.74
18 0.91 0.79 0.23
19 0.89 0.13
20 0.51 0.51 2.18
21
22 0.15 0.20
23 2.16 1.65 0.81
24 1.40 1.57 0.20
25 0.20 9.78 0.20 0.18
26 2.03 0.28 2.36
27 2.36 0.28 1.32 1.04
28 0.36
29 0.46 4.34
30 1.57 3.40
31 0.08 0.38
TCJl'AL 6.02 1.50 2.77 5.59 10.27 34.07 22.37 14.34 11.70 tl.96 2.53 4.73
-------
Table 5.
Rainfall recorded daily at the SWAP citrus 9rove near Fort Pierce, Florida
during 1975.
Date
Jan. Feb. Mar. Apr. ~ June July Aug. Sept. Oct. NoV. Dec:.
975 Rainfall ( c:m)
1 0.64 0.05 0.51
2 1.02 1.52 1.40 1.09
3 0.15 0.23 0.10 0.76
4 0.38 0.25 0.30
5 0.20 1.27 1.14 0.89
6 0.94 0.89 0.15 0.23
7 3.00 0.64 0.10 0.28
8 0.13 1.02 1.02
9 0.38 0.89 0.64 0.38 0.64 3.56 0.33
10 0.74 0.51 2.03 0.74
11 0.74 1.,40 0.51 0.38 0.25 1.37 0.05
N 12
N
13 0.10 1.40 2.67 0.05 0.89
14 0.66 0.20 1.80 1.65 0.03 0.13 0.43
15 0.05 0.25 0.05 0.33 0.13 0.15
16 2.44 4.83 0.13 0.05
17 1.40 0.15 0.05
18 0.64 0.89 3.18 1.52
19 2.29 0.64 2.41 0.13 0.64 0.51
20 0.25 0.30 0.25 4.85
21 2.79 0.05 0.13 0.91
22 1.27
23 4.38 0.15 1.35 0.33
24 1.80
25 0.43 0.13
26 1.40 0.43 0.20
27 0.13 1.02
28 2.34 1.78 0.76 3.56
29 9.40 2.03 0.58 0.38 1.52 0.05
30 0.76 1.65
31 0.25 0.05
TOTAL 1.21 9.'ft 4.20 4.09 26.31 11.45 9.80 8.18 24.77 5.63 7.67 3.09
-------
Table 6. Mean monthly concentrations and tot a I discharges of N03-N and PO~-P per hectare
in subsurface drainage water in the $T 5011 management treatment during 1973-
1975 as a function of rainfall, total drainage, and water table height.
Year Month Ra i n I rri at ion
cm (cm)
1973 Jan 7: 40 I. 42 5.30 420.70 2.610 a 6.20 a
Feb 5. II 0 5.30 362 . 80 .580 a I. 60 a
March 5.39 3.39 5.27 253.90 .520 a 2.05 a
Apri 1 4.75 3.62 5.27 159.20 .550 a 3.45 a
May 13.70 3.47 5.30 365.40 1.750 .066 4.80 .18
June 16.80 0 5.39 995.40 9.660 .438 9.70 .44
Jul y 18.55 I. 48 5.43 1034.26 6.250 .486 6.30 .47
Aug 23.93 3.99 5.58 2147.57 4.158 .981 I. 94 .46
Sept 13.20 0 5.46 1093.32 3.354 .869 3.07 .80
Oct 20.31 0 5.46 1376.43 I. 998 .881 I. 45 .64
Nov I. 96 1.56 5.27 95.59 .040 .019 .42 .20
Dec 3.54 1.65 5.21 26.70 .011 .005 .42 .20
Total 134.64 20.58 5.35 8331.30 31. 751 3.745 3.81 .45
1974 Jan 6.02 1.63 5.30 371.74 .283 .011 .76 .03
Feb 1.50 3.39 5.21 0.49 .001 .000 1.94 .35
Harch 2.77 18.10 5.33 1115.79 14.257 .367 12.78 .32
Apri 1 5.59 1.99 5.18 0.34 .001 .000 4.38 .06
May 10.27 9.73 5.30 882.45 7.165 .215 8.12 .2S
June 34.07 0 5.49 2093.68 15.601 .776 7.45 .37
July 22.37 0 5.49 1658.14 4.306 .619 2.60 .37
Aug 14.34 0 5.39 834.61 .572 .588 .68 .70
Sept 11.70 0 5.30 337.86 .051 .181 .14 .48
Oct 9.96 1.97 5.39 930.48 3.989 .310 4.29 .33
Nav 2.53 1. 85 5.21 2.69 .002 .001 .70 .21
Dec 4.73 0 5.27 203.11 I. 989 .071 9.79 .35
Total 124.85 38.66 5.32 8470.38 48.217 3.132 5.69 .37
1975 Jan I. 21 1.81 5.21 0.13 .000 .000 .06 .25
Feb 9.97 5.92 5.38 825.52 4.194 .133 5.08 .16
March 4.20 2.44 5.32 391.63 .901 .063 2.30 .15
Apri I 4.09 5.57 5.28 169.86 .806 .022 4.75 .13
May 26.31 1. 93 5.41 1536.24 5.711 .362 3.72 .24
June 11.45 3.89 5.40 807.54 4.962 .222 6.14 .27
July 9.80 I. 69 5.28 328.26 2.187 .100 6.66 .30
Aug 8.18 I. 14 5.27 178.68 .702 .051 3.93 .29
Sept 24.77 0 5.43 1299.06 16.991 .830 13.08 .64
Oct 5.63 I. 67 5.34 577.74 7.794 .516 13.49 .89
Nav 7.67 I. 79 5.27 282.68 1.160 .161 4.13 .56
Dec 3.09 I. 81 5.26 41. 20 .246 .014 5.96 .33
Total 116.37 29.66 5.32 6438.54 45.653 2.467 7.09 .38
ClP04-P was not determi oed 00 these samp 1 es.
*The e levat ion of the 5011 surface was 6.40 m above mean sea level.
23
-------
Table 7. Mean monthly concentrations and total discharges of N03-N and P04-P per hectare
in subsurface drainage water in the DT soi 1 management treatment during 1973-
1975 as a function of rainfall ~ total drainaqe. and mean water table height.
Water* Water
Year Month Table He; ht Flow
a
1973 Jan 7.40 I. 42 5.43 331. 0 1.026 a 3.10 a
Feb 5. II 0 5.39 270.4 0.314 a I. 16 a
Ma rch 5.39 3.39 5.30 102.4 0.133 a I. 30 a
Apr; 1 4.75 3.62 5.24 75.4 0.139 a 1.84 a
Hay 13.70 3.47 5.27 22 I. 6 0.525 0.018 2.37 0.07
June 16.80 0 5.55 805.9 4.191 b 5.20 b
July 18.55 I. 48 5.58 804.0 2.565 b 3.19 b
Aug 23.93 3.99 5.76 1576.2 1.245 0.259 0.79 0.16
Sept 13.20 0 5.64 749.8 0.101 0.174 0.13 0.23
Oct 20.31 0 5.67 811. 2 0.093 0.218 0.11 0.27
Nov I. 96 I. 56 5.36 162.9 0.030 0.008 0.18 0.05
Oec 3.54 I. 65 5.24 30.9 0.004 0.018 0.12 0.06
Tota I 134.64 20.58 5.45 5849.8 10.364 0.679 1.77 0.11
1974 Jan 6.02 I. 63 5.36 194.37 0.126 0.011 0.65 0.05
Feb I. 50 3.39 5.21 14.44 0.005 0.003 0.32 0.20
March 2.77 18.10 5.52 589.43 0.655 0.075 I. 11 0.13
Apr! 1 5.59 I. 99 5.27 58.43 0.014 0.008 0.24 0.14
May 10.27 9.73 5.43 357.98 0.543 0.023 I. 52 0.06
June 34.07 0 5.67 871 .21 0.858 0.091 0.99 0.10
July 22.37 0 5.82 1259.00 1.146 0.113 0.91 0.09
Aug 14.34 0 5.70 502.52 0.121 0.201 0.24 0.40
Sept 11.70 0 5.42 147.28 0.026 0.029 0.18 0.20
Oct 8.96 I. 97 5.55 364.73 0.242 0.141 0.66 0.39
Nov 2.53 I. 85 5.24 18.16 0.001 0.007 0.05 0.38
Oec 4.73 0 5.33 5.84 0.001 0.002 0.09 0.42
Total 124.85 38.66 5.46 4383.42 3.737 0.705 0.83 0.16
1975 Jan I. 21 I. 81 5.17 0.00 0.000 0.000 0.00 0.00
Feb 9.97 5.92 5.37 64.29 0.000 0.001 0.01 0.01
March 4.20 2.44 5.45 182.51 0.011 0.000 0.06 0.00
Apri I 4.09 5.57 5.35 130.26 0.016 0.000 0.12 0.00
May 26.31 I. 93 5.50 454.68 0.064 0.000 0.14 0.00
June 11.45 3.89 5.60 531.96 0.084 0.000 0.16 0.00
Jul y 9.80 I. 69 5.36 198.42 0.028 0.000 0.14 0.00
Aug 8.18 I. '4 5.26 102.73 0.012 0.000 0.14 0.00
Sept 24.77 0 5.50 433. 32 0.076 0.000 0.18 0.00
Oct 5.63 1.67 5.52 340.38 0.035 0.010 0.10 0.03
Nov 7.67 I. 79 5.37 148.08 0.010 0.004 0.07 0.03
Oec 3.09 1.81 5.31 59.46 0.021 0.000 0.35 0.00
Total 116.37 28.66 5.40 2646.09 0.358 0.015 0.14 0.01
.P04-P was not determined on these samp 1 es.
bThese d i scha rge va I ues were less than 0.01 kg of N03-N.
JrThe elevation of the soil surface was 6.28 m above mean sea level.
24
-------
Tab Ie 8. Mean monthly concentrations and totaT discharges of NOrN and P0z.-P per hectare
in subsurface drainage water in the DTL soil management treatment during 1973-
1975 as a function of rainfall. total drainage, and mean water table height.
Wa te r 1'1 Water
Year Month Table Hei ht F I ow
(m m Iha
1973 Jan 7.40 I. 42 5.58 133.23 0.510 a 3.80 a
Feb 5.11 0 5.58 114.94 0.210 a I. 80 a
Ma rch 5.39 3.39 5.46 42.69 0.080 a I. 90 a
Apr! 1 4.75 3.62 5.43 30.54 0.070 a 2.45 a
May 13.70 3.47 5.43 83.17 0.250 0.005 3.00 0.06
June 16.80 0 5.64 444.18 4.490 b 10.10 b
July 18.55 I. 48 5.70 221. 25 0.890 b 4.00 b
Aug 23.93 3.99 5.97 780.97 1.248 0.124 I. 60 0.16
Sept 13.20 0 5.85 564.07 0.155 0.108 0.27 0.19
Oct 20.31 0 5.88 519.18 0.050 0.091 0.10 0.18
Nov 1.96 I. 56 5.55 33.57 0.165 0.005 0.49 0.14
oec 3.54 I. 65 5.36 0.07 0.000 0.000 0.49 0.14
Total 134.64 20.58 5.62 2968.66 7.970 0.332 2.68 0.13
1974 Jan 6.02 1.63 5.46 93.14 0.084 0.009 0.90 0.10
Fob I. 50 3.39 5.33 0.07 0.000 0.000 1.69 0.29
Ma rch 2.77 18.10 5.67 501.02 5.139 0.111 10.26 0.22
Apri 1 5.59 I. 99 5.39 0.16 0.000 0.000 2. 10 0.14
May 10.27 9.73 5.49 280.04 3.329 0.021 II. 89 0.08
June 34.07 0 5.82 809.79 3.411 0.122 4.21 0.15
July 22.37 0 5.97 652.81 0.905 0.252 I. 39 0.39
Aug 14.34 0 5.82 296.94 0.123 0.146 0.41 0.49
Sept 11.70 0 5.55 75.35 0.015 0.017 0.20 0.23
Oct 8.96 I. 97 5.67 338.74 0.330 0.177 0.97 0.52
Nov 2.53 I. 85 5.38 0.02 0.000 0.000 0.18 0.22
oec 4.73 0 5.43 12.50 0.003 0.006 0.23 0.50
Total 124.85 38.66 5.58 3060.58 13.339 0.862 4.36 0.28
1975 Jan I. 21 I. 81 5.29 0.00 0.000 0.000 0.00 0.00
Feb 9.97 5.92 5.46 233.64 0.149 0.003 0.64 0.02
Ma rch 4.20 2.44 5.56 105.29 0.094 0.000 0.89 0.00
Apr i 1 4.09 5.57 5.45 26.47 0.003 0.000 0.12 0.00
May 26.31 I. 93 5.58 426.10 0.971 0.000 2.28 0.00
June 11.45 3.89 5.76 371.31 0.316 0.000 0.85 0.00
July 9.80 I. 69 5.49 80.05 0.082 0.000 1.02 0.00
Aug 8.18 I. 14 5.38 12.12 0.015 0.000 0.12 0.00
Sept 24.77 0 5.65 372.68 1.229 0.014 3.30 0.04
Oct 5.63 I. 67 5.72 219.53 0.669 0.019 3.05 0.09
Nov 7.67 I. 79 5.53 83.70 0.120 0.007 I. 43 0.09
oec 3.09 I. 81 5.45 12.03 0.013 0.001 1.06 0.09
Total 116.37 29.66 5.53 1942.92 3.646 0.044 1.88 0.02
ap04-p was not determined 00 these samp I es.
bThese P04-P concentrations were less than 0.04 ug/ml.
*The elevation of the soil surface was 6.40 m above mean sea level
25
-------
FIGURE 4.
Ci1 m_- 5 T
£
",- 2 -DT
5 _._.- DT L
~ 15
CI
L.
I1J
.s:;
U
111
i5
L.
G>
ni
3:
0 4 6 8 12
Time (months)
1973
,,1 '----ST 1
-DT
-'-'-DTL
co 14
£ 10
0. ,
~ "
"
"0 8 : \
, '\
G> ,
CI '
L. 6 .
I1J ' .
, .
£ '
, .
u ,
111 4 " 0,
i5 ' 0 ,
, 0 0
, '
~ 2 . . .
'" .. ' .
o ......... .
Z 0
2 4 6 8 10 12
Time (months)
1973
co
£
0.
15
G>
C)
L.
I1J
£
U
.~
o
a..
I
0'<1
a..
h
:' "'''''''""""".,
, .
, .
,/ \
. .
. .
,........." \
. .
. '
. .
, .
~/ \
,: .".-.-.-.- \
, .".' ". '
UU'ST
-DT
-.-. DT L
200
o
2
4 6 8
Time(months)
1973
12
10
Total monthly discharges of drainage
from ST, DT, and DTL soil management
fa r I 973 .
water, N03-N, and P04-P
plots plotted with time
26
-------
FIGURE 5.
ro m-- 5T
.c
,ry- 2000 -OT
.5 -.-"- OTL
"D
i!J 150
01
L
(1j
.c 1000
u
.'!:>
0
L 500
i!J
+'
(1j .'
:s: "
12
:1 5T--m 1
OT-
~ /\ DTL-.-.-
(1j
.c 'L ~ .L
0> 10 TT T T
" .
2S " , .
, . .
"D . ,
, , "
i!J 8 ' . "
. .
01 , , .
L .' I
(1j " : '
5 " ,
.c , . ,
., .
u , ". ' ,
'!:> I 1\ ~ , .
,
0 4 : i '. \ ' !,
'
:! \ 1 I ,'-'-,
~ .! "': ' ,
,/ \ , ' .
2 :.' \\ ' .
,. \. "
ro ., \~ :.1 . ". '
o '" \ ~,/
'! ~:! . '
Z ". ' -'-
0
6 8 10 12
Time (months)
1974
1200 u--- 5 T
ro 1000 -OT
.c -.-. OTL
:9
"D 80
i!J
01
L 600
(1j
.c
u
.'!:> 400
0
0, 200
0
CL 0
1974
Total monthly discharges of drainage
from ST, DT, and DTL soil management
for 1974.
water, N03-N and P04-P
plots plotted with time
27
-------
FIGURE 6.
eu
.I::
'1 2000
-0
~ 1500
L-
eu
-5 1000
I/)
o
L-
a.>
1U
?;
no... 5 T
-OT
-.-.- OTL
500
2
4 6 B
Time (months)
1975
12
16
~
.I:: 1
0, 10
~
-0
a.> B
O!
L-
eu
.I:: 6
u
I/)
0 4
Z
, 2
M
o
Z
0
-----5T
-OT
-'-'-OTL
~,
"
: \
, ,
I ,
.:. 1.
T \
.
, '
.
: \
.
,
, ,
'''.. 'I
: "", : '
'. ,
,. . ~ I \
:" " \. : '-
/\ ,: \: \
: \,.' ". : "
,/ \.....1 - ''''..J'''/'''''''''''''''....''''''-L-
....0' '''''''''-'-, ~".
2
4 6 B
Time (months)
1975
10
12
~
.I::
:9
-0
a.>
O!
L-
eu
.I::
u
I/)
o
a..
I
0"
a..
I,
,.
. .
: \
, ,
I .
" \
, ..
, .
,".. : \
, " I ,
,... , ..
, " I \
" '" \
.,,"''''''''..............,/ """''''''''/ """'''''''.
120C
uu- 5T
-OT
_._. OTL
4 6 B
Time (months)
1975
10
12
1000
800
60C
400
200
o
2
Iota1 month1y discharges of drainage
from ST, DT, and DTL soil management
for 1975.
water, N03-N and P04-P
plots plotted with time
28
-------
to the ST plot was observed earl ier by Stewart and Alberts (1971) and can
be ex~lained primarily by two phenomena: a decrease in the hydraul ic con-
ductivity (Hammond et aI., 1971) of the soi 1 (0-85 cm depth) occurred due
to mixing of subsoi 1 spodic and sandy clay horizons with the sandy surface
(AI and A2 horizons) soil and a partial "cloggingl! of the flow medium in
the immediate vicinity of DT and DTL drains was observed (Rogers, 1971 and
Rogers and Stewart, 1974). Using an electrical analog, Rogers (1971) showed
that if "clogging" had not have occurred drainage flows from DT and DTL
plots should have exceeded that for ST due to the greater effective volume
of soil drained. The "clogging" of DT and DTL drains has been partially
attributed to the deposition of suspended and dissolved colloidal organic
matter in the porous material imm2Jiately surrounding the drain tubes fol-
lowing the deep tillage operation. Fiskell et al. (1970) have shown exper-
imentally that under conditions of low soluble salts organic matter can be
partially dissolved and move with soil water for Oldsmar fine sand. By
increasing the level of soluble salts either in the soil or in the infiltra-
ting water mobil ity of the organic material could be suppressed by preventing
flocculation of the negatively charged colloids. The mechanical action of
the deep tillage operation in conjunction with heavy rainfall which occurred
soon afterwards probably resulted in the transport of suspended and dissolved
organic material with water toward the drain tubes where deposition and/or
filtering occurred. Activity of soil microorganisms is also another possible
contribution to the "clogging" effect of the drains. The overall effects of
the decreased drainage flow in the deep-tilled plots relative to the shallow-
til led plot were decreased infiltration rates which increased the probability
for surfAce runoff during intense rainfall and decreased time-response for
removal of excess water from the root zone of the soil following a large rain-
fall event. The slower drainage response in DT and DTL plots also tended
to provide higher soil water contents at a given time than in the ST plot.
Hammond et al. (1971) also found that the water-holding capacity of the
deep-tilled soils were sl ightly higher than for the shallow-tilled soil.
Periods of greatest monthly discharges of water, N03-N and P04-P in sub-
surface drains from ST, DT, and DTL plots (Figs. 4, 5, and 6) were generally
associated with periods of greatest monthly rainfall (Tables 6, 7, and 8). Dis-
charge of water, N03-N, and P04-P occurred during March ~ndMay through October
for 1973, during March and May through October for 1974, and February, May-
July, and September-October for 1975. In all cases discharge of water and
nutrients was much higher from ST than from either DT or DTL plots. The
greater water flows through the ST soil and out into the drain tubes
resulted in much greater losses of N03-N and P04-P with subsurface drain-
age than for DT and DTL treatments. Mean monthly discharge of both N03-N
and P04-P with drainage water occurred in the order: ST> DTL ~ DT. Although
the water flow in DT drains usually exceeded that from DTL, discharge of
N03-N with drainage was frequently greater from the DTL plot. Discharge of
P04-P in drainage was usually similar for DT and DTL plots. Total quantities
of N03-N discharged with subsurface drainage during 1973, 1974, and 1975
were 31.75, 48.22, and 45.77 kg/ha for the ST plot (Table 6); 7.97, 13.34,
and 3.65 kg/ha for DTL (Table 8); and 10.36, 3.74, and 0.36 kg/ha for DT
(Table 7).
29
-------
Discharge of P04-P with subsurface drainage was always several-fold less
than N03-N discharge for all three soil management treatments. Total amounts
of P04-P discharged in subsurface drainage during 1973, 1974, and 1975 were
3.75,-3.14, and 2.47 kg/ha for the ST plot; 0.33, 0.86, and 0.04 kg/ha for
DTL; and 0.68, 0.70, and 0.01 kg/ha for DT (Tables 6, 7, and 8). The total
quantity of N applied each year was 9.2 times larger than that for P. The
ratios of the quantities of N03-N actually discharged with drainage to the
quantities of P04-P discharged varied considerably from 9.2. During 1973-
1975 the ratio of N03-N to P04-P increased from 8.5 to 18.5 for the ST plot.
During the same period this same ratio also decreased from 13.7 to 3.8 for
the DT plot, and decreased from 18.6 to 15.2 for DTL. Although many fac-
tors affect this ratio, an increase in the ratio possibly indicates an
increase in N03-tJ discharge with a corresponding discharge of P04-P.
Detailed interoretation of these changes in the ratios of N03-N and P04-P
discharges i~ not attempted at this time.
Monthly discharge amounts of N03-N and P04-P in drainage from ST, DT,
and DTL plots is presented in Table 9 for six wet months (May-October) and
in Table 10 for six dry months (November-April) for the period 1973-1975.
These data are in agreement with the findings of Calvert and Phung (1971)
who observed that NO -N loss with drainage water was much greater during
periods of high rainfall and thus high drainage discharge. Later Calvert
(1975) concluded that maximum discharge as well as concentration of ferti-
1 izer nutrients was greatly dependent upon rainfall plus irrigation amounts
and upon timing of fertil izer appl ications with respect to the average rain-
fall distribution.
The highest mean monthly concentrations of N03-N in drainage from the
ST plot were found for the ST drainage during the wet seasons for these
three years. Subsurface drainage water from the DTL plot actually developed
higher N03-N concentrations during 1973 and 1974 wet seasons than did water
from the ST drain. This result may be attributed to a greater nitrification
rate in DTL than in ST and DT soil treatments (Phung, 1972). Only in the
wet 1974 year was concentration of N03-N from DTL higher than from the ST
drain during the dry season. The N03-N concentration in ST drain water in
the dry months within the three years ranged from 0.39 to 6.2 wg/ml. The
unusually high discharge of N03-N from ST that occurred in the wet season
of 1975 is believed to have been influenced by two major rainfall events
which occurred in May and September. The rainfall distribution in 1975 was
such that 26% of the annual rainfall (116.4) occurred during the dry six-
month period as compared to only 21% (134.6 cm annual rainfall) and 19%
(124.9 cm rainfall) during 1973 and 1974, respectively. Discharge of POb-P
was considerably less than discharge of N03-N, but more P04-~ was leached from
the ST soil profile relative to DT and DTL and' discharged from the drain
during each of the three years of the study. DT and DTL drains usually
discharged disimilar amounts of N03-N, but similar amounts of P04-P into
the drain water.
Maximum discharge of P04-P occurred
rainfall months of 1973 and 1974 (Figs.
of P04-P occurred from DT and DTL plots
and 1974, but virtually no discharge of
from the ST drain during the high
9 and 10). Substantial discharges
only in the rainy periods of 1973
P04-P occurred from these plots
30
-------
Table 9.
Six-month means for N03-N and P04-P concentrations and discharge
surface drainage from ST, DT, and DTL soil management treatments
fluenced by rainfall and total drainage. Data for six-month wet
(May through October) are presented for 1973-1975.
in sub-
as in-
per iods
Year
1973
\.N
1974
1975
Ra i n fall
cm
106.49
101071
86.14
Chemical
NOrtl
II
P04-P
II
II
NO~-N
II
P04-P
II
II
tlO~-tJ
II
P04-P
II
II
Soi 1
Treatment
ST
DT
DTL
ST
DT
DTL
ST
DT
DTL
ST
DT
DTL
ST
DT
DTL
ST
DT
DTL
Total
Chemical
D i scha r ed
ha
70.12
49.68
26. 13
70. 12
49.68
26.13
67.37
35.03
24.54
67.37
35.03
24054
3.87
1.76
2.71
0.53
0.13
0.12
47.28
20.61
14.82
II] . 28
20.61
14.82
4070
0.84
3.31
0.110
0.16
0.30
8. 11
0.14
2.21
0.44
0.00
0002
.'.
AOne cm of drainage is equivalent to 100 M3/hao
1045-9.70
0.11-5.20
O. 1 0- 100 1 0
0018-0.80
0.00-0027
0.00-0.19
0014-8012
00 18-1 .52
0.20-11.89
0.25-0.70
0006-0.40
0.08-0.49
3.72-13.49
0.10-0.18
0.12-3.30
0024-0.89
0.00-0.03
0.00-0.09
27017
8072
7.08
3.72
0.67
0.33
3 1 . 68
2.94
8. 11
2.69
0.58
0.74
38.35
0.30
3.28
2.08
0.01
3.03
-------
Table 10.
Six-month means for N03-N and P04-P concentrations and discharge
surface drainage from ST, DT, and DTL soil management treatments
fluenced by rainfall and total drainage. Data for six-month dry
November through April) are presented for 1973-19750
Year Ra infa 11
(em)
Chemical
Soi 1
Treatment
1973
I.N
N
1974
1975
28.15
~JO ~ - N
ST
DT
DTL
ST
DT
DTL
Dra i nage>',
(cm)
Chemical Concentration
Mean Range
(~g/m1) (~g/ml)
13. 19
9.73
3.55
13019
9.73
3.55
16.94
8.81
6.07
16.94
8.81
6.07
3.?8
1.69
2.92
0.52
0.12
o. 17
II
P04-P
II
II
23014
tJO~-tJ
ST
DT
DTL
ST
DT
DTL
9.76
0.91
8.61
0.26
0.12
0.21
17. 11
5.85
4.61
17. 11
5.85
4.61
4.30
0.10
0.82
0.23
0001
0.02
II
P04-P
II
II
30.23
NO~-N
ST
DT
DTL
ST
DT
DTL
.'.
~One cm of drainage is equivalent to 100 M3/ha.
II
P04-P
II
II
0042-f1.20
0.12-3.10
0.49-3.80
0.47-0057
0008-0.16
0.16-0.18
0070-12.78
0.05-1.11
0.18-10.26
0.03-0.35
0.05-0.42
0.10-0.50
0.06-5.96
0.01-0.35
0.12-1.43
0.13-0.56
0.00-0.03
0.00-0.09
in sub-
as in-
periods
Total
Chemical
Discharged
(ha)
4033
1.65
1.04
0.07
0.02
0.01
16.53
0.80
5.23
0.45
O. 11
0.13
7031
0.06
0.38
0.39
0.01
0.01
-------
~E
c u
'01 --
0:: 5 20
~+i
-~
:501
c'-
o t
2:-
-"0
~ c 10
+-,CU
o
I-
FIGURE 7.
30
o
1973
-----1974
-.-. 1975
1\
1 \
1 \
, \
, \
.0 I \
I' I \
.. I \
I \ 1 ,
., ,
i 1\ \
. ,. "
i\ I : \ '
1\ ., \
, \ I "
,\ . ,
, \ I ,
J\.! \ i,'
/\J \.,
I ,\ \ !
i ' \ \
I
I
I
\
\
\
\
\ .
. \ I
~ \ .
., 'l-
. . '
, I ""-_.
.. ~\.."
...... , \ \
."'" . \
\ \
£-' \
\
J.
2
6 8
Time (months)
12
10
4
Total monthly amounts of rainfall and irrigation for ST, DT,
and DTL plots plotted with time for the period 1973-1975.
33
-------
Q)
u
~
L........
~E
VI u
.0"'-'-50
~Q)
iflQ)
"0 OS
Cc
OS°CU
Q)L
ua
~ 25
L
~
ifI
OS
+-'
~
FIGURE 8.
(1975)
(1973)
(1974)
ST plot
Control
plot
DT plot
DT L plot
165
Total annual quantities of surface and subsurface drainage plotted
versus total amounts of rainfall plus irrigation for 5T, DT, DTL,
and Control soil management plots for the period 1973-1975.
75
o
145
;'
;'
;'
;'
,-
,-
;'
150 155 160
Total Rainfall and Irrigation (em)
34
-------
.......
E
~
c
o
+-'
~
L
Q.
(/)
C
~
b 100
o
Q.
~
>
W
125
-0
-------
........
~ 60
-
(J)
.::L.
'-"
"0
Q)
(J)
L
CU 40
..c:
u
(/)
o
Z
I
OM 20
Z
CU
+-'
~
FIGURE 10.
(1975)
(1973)
(1974)
ST plot
DTL plot
"....
........
......
-...
o
145
o/"DT plot
- - - Control
...............~------------~ plot
150 155 160 165
Total Rainfall and Irrigation (cm)
Total N03-N discharged annually with surface and subsurface
drainage water versus total amounts of rainfall plus irrigation
for ST, DT, DTL, and Control soil management plots for the
period 1973-1975.
36
-------
during 1975, even in the rainy period. Discharges from DT and DTL in the
rainy period of 1975 amounted to less .than 0.2 kg/ha/mo of P04-P. That
amount of P04-P was considered to be negl igible. Monthly maximum discharges
of P04-P in drainage from ST were 1.0, 0.8 and 0.8 kg/ha, respectively, in
1973, 1974 and 1975. These maxima occurred in August 1973, June 1974, and
September 1975, respectively.
Surface runoff was recorded for each major rain event from September
1973 through December 1975. Surface runoff was largely J imited to the DT
and DTL plots (Table 11) since the ST plot had an ultimate infiltration
rate (see saturated hydraul ic conductivity values in Table 1) sufficient
to preclude the occurrence of runoff from the surface. Runoff was detected
from the ST plot (Table 11) only during extemely high intensity rains. The
maximum runoff values for the three years were 0.11, 6.27 and 4.69 cm for
ST, DT and DTL plots and occurred in June, 1974, after 34 cm of rainfall.
Only 1.7 g of N03-N was detected in the total runoff water from ST at this
time in contrast to 138 g and 103 g of N03-N in the runoff from DT and DTL,
respectively (Table 11). Maximum mean concentrations of N03-N in composite
samples of surface runoff were 3.4 wg/ml for ST in September 1973; 12.4 Wg/
ml for DT and 12.6 wg/ml for DTL in March 1975. Total discharge of N03-N
however, was negl igible during these timp~ because of very small total flows
of water. During 1975, rainfall was low during the normally rainy summer
months, and the largest runoff was associated with intensive rainfall events
(26.31 cm) in May. Runoff from ST was negl igible (0.16 cm) during May and
was considerably higher from DT (3.66 cm) and DTL (4.37 cm) (Table 11).
Surface losses of N03-N and P04-P usually were less than 1% of that
applied as fertil izer except in 1974 the P04-P loss from the DT and DTL
drains amounted to 2.0% and 1.7%, respectively. Loss of N03-N from the
control 1 ine was low except in 1975 when an amount of N03-N approximating
7.3% of the N applied to the fertilized plots in SWAP was discharged from
the unfertil ized Control 1 ine. Also, the unfertil ized Control line dis-
charged sizeable quantities of P04-P in 1973 and 1974 which were equivalent
to a fertil ized plot loss of 4.4 and 5.~%, respectively.
Water quality data obtained in the 3-year study from sampl ing locations
7, 8 and 9 (Figure 2) at the Central Sump, South Sump, and Control drain,
respectively are presented in Table 12. Months having peak water flows
from the unfertilized Control plot coincided with peak flows from the Cen-
tral and South Sumps. Maximum concentrations of N03-N in drainage from the
Control plot (Table 11) were generally small. During 1973 concentrations of
N03-N in water from the Control plot were much lower than in drainage from
ST, DT and DTL. In 1974 the N03-N concentration for the Control was lower
than for ST and DTL, but greater than for DT. However, during 1975 N03-N
concentrations for the Control were much higher than N03-N concentrations
for both DT and DTL. The reason for the higher N03-N concentrations in the
drainage from the Control during 1975 is not immediately clear, but presum-
ably some nitrification occurred. Since the Control plot was not fertil ized,
assay of control drainage water provides a check on the amount of N03-N pro-
duced by natural means such as nitrification of organic matter and nitrate
fixation during electrical activity from thunderstorms.
37
-------
Table 11.
Mean monthly concentrations and
water from surface tilled (5T),
soil management treatments as a
and 1975.
total discharges of N03-N
deep tilled (DT) and deep
function of rainfall
and P04-P in surface runoff
tilled plus 1 imestone (DTL)
during-1973, 1974,
Surface Tilled Deep Tilled Deep Tilled Limed
Rain Water 'Q3-N ~-p N?3-11 ~-p Water N03-N P04-p NOr' P04-p Water N03-N P04-p N03-N P04-P
[.:onth fall Runoff Cone. Cone. D18e . DlIe . Runoff Cone. Cone. Di e. Dile. Runoff Cone. Conc. Disc. Disc.
-CIII- mj/ha -----PIII----- ------g------ mj fha -----prm----- ------1------ m..1/ha -----ppm----- ------g------
1973
Sept 13.20 3.97 3.40 0.30 13.50 1.19 108.21 1.53 0.30 165.56 32.46 203.80 4.54 0.36 925.25 73.37
Oct 20.31 2.80 1.00 0.20 2.80 0.56 357.14 0.44 0.20 157.14 71.43 287.52 - 0.80 0.30 230.02 86.26
i:ov 1.96 0.00 b.oo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Dec 3.54 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1974
Jan 6.02 0.25 0.00 0.00 0.00 0.00 6.12 0.00 0.00 0.00 0.00 10.17 0.00 0.00 0.00 0.00
Feb 1.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
IJ..) lIlILr 2.77 0.00 0.00 0.00 0.00 0.00 98.38 4.06 0.59 399.42 58.04 119.13 3.56 0.60 424.10 71. 48
ex> Apr 5.59 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 nsnf nsnf 0.00 0.00
~1ay 10.27 3.48 0.30 0.10 1.04 0.35 20.96 3.12 0.74 77.97 15.51 55.36 3.76 0.44 208.15 24.36
June 34.07 10.67 0.16 0.22 1.71 2.35 626 .67 0.22 0.37 137.87 231. 87 469.08 0.22 0.31 103.20 145.41
July 22.37 0.57 0.00 0.67 0.00 0.38 137.67 0.46 0.31 63.33 42.68 128.48 0.61 0.23 78.37 29.55
Aug 14.34 0.67 0.00 0.45 0.00 0.30 23.20 0.06 0.41 1.39 9.51 43.13 0.04 0.76 1.73 32.78
Sept 11.70 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 1.08 0.00 0.00
Oct 8.96 1.62 0.30 0.07 0.49 0.11 54.55 0.15 0.27 8.18 14.73 62.06 0.11 0.28 6.83 17.38
['lov 2.53 0.00 0.00 0.00 0.00 0.00 0.00 nsnf 0.00 0.00 0.00 0.00 -0.00 0.00 0.00 0.00
Dec 4.73 0.00 0.00 0.00 0.00 0.00 0.15 nlnra nsnf 0.00 0.00 1.34 bmdl bDdl bDdl bDdl
1975
Jan 1.21 0.00 0.00 0.00 0;00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Feb 9.Cff 1.85 bI8Ilb badl bmdl bmdl 28.90 bmdl bmdl badl bmdl 74.36 bDdl bDdl bmdl bmdl
Mar 4.20 0.07 nanf nanf nlnf nanf 0.97 12.40 0.25 12.03 0.24 1.66 12.60 0.25 20.92 0.42
Apr 4.09 0.03 nlnt' nanf nanf nlnt 0.06 nsnf nsnf nsnt' nlnf 0.23 nanf Dsnf nsnf nsnf
May 26.31 16.00 0.89 0.46 14.24 7.36 366.00 0.64 0.34 234.24 124.44 437.00 0.93 0.34 406.41 148.58
JUDe 11.45 0.15 naDt naDt nant nant 1.48 0.20 1.40 0.30 2.07 0.79 0.27 2.80 0.21 2.21
July 9.80 0.05 naDt DInt Dint DlDt 0.07 DInt naDf naDt DlDf 0.28 0.65 0.88 0.18 0.25
Aug 8.18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.16 nsnt DInt DBDf nSDf
Sept 24.17 3.30 0.20 1.22 0.66 4.03 41. 75 0.17 0.54 7.10 22.55 139.20 O.oe 0.51 11.14 70.99
Oct 5.63 0.03 Dint nlnt bmdl badl 1.20 0.18 2.01 0.22 2.41 2.44 0.14 0.61 0.34 1.49
Nov 7.67 1.80 1.39 0.20 2.50 0.36 1.96 0.30 0.30 0.59 0.59 3.75 0.52 0.46 1.95 1.73
Dec 3.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
a nant, no nmp).el were taken due to negUgible flaw.
b 11811, concentration 1f88 below the miniDm detection level. Minimllm detection levels for N03-N and ~-p are 0.04 PIIII and 0.06 PIIII, respectively.
Dilebarp valuel tor concentration. lover than thele levels were not calculated.
-------
Drainage from the Control also contained detectable levels (ranged from
0.06 to 0.49 ~g/ml) of P04-P during at least one month out of each of the
three years in the study. Again, as with nitrate, both concentrations and
total discharge of P04-P from the Control drain appeared to increase for a
short period then decrease as both rainfall and total flow increased (Table
12), thus indicating miscible displacement between infiltrated water and
the soil solution as flow occurs in the soil.
Significant discharges of N03-N and P04-P through the South and Central
Sumps usually coincided with significant discharge from the subsurface drains
from the three soil treatment plots (Table 12).
Monthly distributions of rainfall plus-irrigation (Fiq. 7) for 1973,
1974, and 1975 were found to be similar in that most of the water was
applied during the wet period from May through October. Otherwise, the
distributions were dissimilar and nonuniform.
A summary of annual quantities of water and nutrient discharge with
surface and subsurface drainage for ST, DT, and DTL plots is given in Table
13 and for the Control in Table 14. During all three years subsurface drain-
age was much greater from the ST plot relative to that for DT and DTL plcts.
Surface runoff, however, was much greater for DT and DTL plots relative to
that for the ST plot. For the ST plot the total annual quantities of surface
and subsurface drainage (Fig. 8) increased with increasing total rainfall
plus irrigation. For DT and DTL plots, total drainage first increased with
rainfall plus irrigation then decreased. For a given quantity of rainfall
plus irrigation the total surface plus subsurface drainage was consistently
in the order: ST > DT > DTL. Surface plus subsurface drainage from the Con-
trol plot at first decreased with rainfall plus irrigation and then increased.
~nnual amounts of evapotranspiration were calculated by subtracting
amounts of surface plus subsurface drainage from total inputs of rainfall
plus irrigation (Fig. 9). Deep percolation losses of soil water were assumed
to be insignificantly small. For any given amount of rainfall plus irriga-
tion, estimates for evapotranspiration were in the order: DTL> DT > ST.
Evapotranspiration for the Control plot was usually of the same order as for
DT and DTL plots. For ST, DT, and DTL plots evapotranspiration at first
decreased with rainfall and then increased. Overall growth and fruit yields
for the entire SWAP citrus grove during 1973-1975 were in a similar order as
for evapotranspiration, ie. DTL> DT> ST. For 1975 average orange yields
were 216, 156, and 167 boxes/ha,-respectively, for DTL, DT, and ST plots.
Average yields of grapefruit during 1975 were 576, 400, 392 boxes/ha, respec-
tively, for DTL, DT, and ST plots. Since these citrus trees were relatively
young it is important to keep in mind that transpirational use of water on
these three plots occurred by both the citrus trees and Bahia sod located
between the rows of citrus. The Control plot, of course, was totally covered
by sod.
Annual quantities of N03-N and P04-P discharged (Figs. 10 and 11) with
surface and subsurface drainage were shown to increase with total rainfall
plus irrigation for the DTL plot. A similar trend was observed for the DT
39
-------
Table 12. Mean monthly concentrations and total discharges of NOrN ancl P04-P in subsurface
drainage water from the unfertil ized Control Plot, Centra 1 Sump, and South Sump
as a function of rainfall, drainage, and water tab 1c height (\.J. T. ht.) during
1973, 1974, and 197'3.
Control Drain Center Sl.IIIIP South Sump
Total II.T. NOJ-N PIJ4-P xu j-:-': P04-P ') otal N()3-~ P04-P N03-~ P04-P lotal K03-~ P"4-P NO]-;\ pn4-J'
~ E.!!.!!f!!! Flow Ht. Cone. Cone. Disc. Disc. Flow Cone. Cone. Disc. Dilc. Flow Cone. Cone. Di se. Di se.
-C1II- ..J/ha -m- - ppm - -kg- m3/ha - ppm - -k~- ..J/ha - ppm - -k\~-
1973
Ian 7.40 dwnl" 5.55 dim! dlml dwni dwni 3430 1. 76 pwndb 6.04 pwnd 6490 1.58 pwnd 10.25 pwnd
Feb 5.11 dwn! 5.72 dim! dim! dvn! dwn1 3270 1.50 pwnd 4.91 pvnd 4850 1.19 pwnd 5.77 pwnd
Mar 5.39 dvn! 5.49 dvn! dvn! dvn! dvn! 1800 1.55 pwnd 2.79 pwnd 1480 1.30 plmd 1. 92 pwnd
Apr 4.75 dwn! 5.41 dim! dim! dwni dim! 1290 4.80 pwnd 6.19 pwnd 1750 1.80 plmd 3.15 pwnd
~Iay 13.70 dwn! 5.32 dim 1 dvn! dvn! dvn! 1780 3.20 pwnd 5.70 pwnd 1800 1.50 plmd 2.70 pwnd
June 16.80 dwn! 5.79 dvn! dvnl dvnl dim! 6980 8.00 pwnd 55.84 pwnd 156]0 2.]0 plmd ]5.95 plmd
July 18.55 dwni 5.93 dim! dim! dvn! dvn! 8720 3.53 0.21 30.78 1.8] 16660 2.50 0.06 41. 65 1.00
Aug 23.93 747 .46c 5.73 0.19 0.15 0.14 0.11 14100 0.70 0.16 9.87 2.26 27680 1.00 0.17 27.68 4.71
Sept 13.20 1478.42 5.62 0.28 0.22 0.41 0.33 10300 2.23 0.28 22.97 2.88 20100 0.17 0.26 ] .42 5.2]
Oct 20.31 1529.83 5.65 0.23 0.25 0.35 0.38 11000 0.75 0.19 8.25 2.09 25100 0.84 0.21 11.08 5.27
Nov 1.96 17.13 5.36 0.24 0.21 tracee trace 1590 1.06 0.20 1.69 0.32 2720 1.35 0.20 3.67 0.54
Dec 3.54 1.95 5.29 n.nfd nlnf nsnf nlnf 690 4.85 0.11 ].35 0.08 651 1. 51 0.14 0.98 0.09
1974 bad I f
JaD 6.02 265.24 5.31 0.96 0.25 bad 1 2670 5.84 0.11 15.59 0.29 3470 1.67 0.08 5.79 0.28
.t:- Feb 1.50 0.79 5.22 nlnf nanf nlnf nlnt 470 0.20 0.08 0.09 0.04 746 0.73 0.15 0.54 O.ll
0 Mar 2.77 0.00 5.14 0.00 0.00 0.00 0.00 2770 5.20 0.21 14.40 0.58 1780 ].31 bald I 5.89 bald I
Apr '.59 0.00 5.11 0.00 0.00 0.00 0.00 480 0.33 '-II 0.16 '-II 1480 0.48 b..:Il 0.71 b..,:Il
~ 10.27 249.64 5.20 0.57 bad 1 0.14 bmdl 2720 6.60 0.19 17.95 0.52 2710 2.76 0.10 7.48 0.27
JII... )4.07 1957.27 5.58 0.80 bad 1 1.57 bad 1 12540 7.35 0.16 92.17 2.01 28620 4.08 0.10 116.77 2.86
July 22.37 1988.88 5.71 0.23 0.49 0.46 0.97 12730 ].25 0.13 41. 37 1.65 29970 1.61 0.34 48.25 10.19
Aul 14.)4 1050. 28 5.64 0.24 bad 1 0.25 '-II 7890 0.38 0.09 ].00 0.71 17010 0.08 0.17 1.]6 2.89
Sept 11.70 403 .69 5.43 0.09 '-II 0.04 bmdl 3210 0.40 0.27 1.28 0.87 5640 0.22 0.14 1. 24 0.79
Oct '.96 608. 12 5.50 0.24 bmdl 0.15 bmdl 6300 4.28 0.23 26.96 1.45 12560 2.16 0.17 27.13 2.14
- 2.53 5.29 5.24 0.14 '-II tree. '-II 590 0.78 0.08 0.46 0.05 1080 0..08 0.07 0.09 0.08
D8c 4.73 75.35 5.36 1.26 b.,cn 0.09 '-II 900 1.03 0.23 0.93 0.21 3400 0.50 0.11 1. 70 0.]7
1915
J.. 1.21 0.00 5.25 n.nf nlnf nlnf n.nf 970 0.50 0.20 0.49 0.19 1030 0.11 0.11 0.11 0.11
Feb 9.97 396.37 5.30 1.74 bI8d 1 0.69 bI8d 1 3710 1.67 0.06 6.20 0.22 5720 1.0] bI8d I 5.89 bald I
Mer 4.20 117.67 5.39 3.72 bI8d 1 0.44 bI8d 1 3060 1.29 bI8d 1 3.95 b8dl ]500 0.60 '-II 2.10 bold 1
Apr 4.09 80.63 5.27 3.68 bI8d I 0.30 '-II 1560 1.38 b8dl 2.15 bnd1 1110 0.13 '-II 0.14 bad 1
Mey 26.31 1437.94 5.45 ].46 '-II 4.98 bI8d 1 7850 1.22 bI8d 1 9.58 bI8d 1 16850 0.14 '-II 2.36 bmdl
June 11.45 431.40 5.49 3.60 0.]5 1.55 0.15 6730 1.70 b8dl 11.44 b8d1 103]0 0.56 '-II 5.78 bmdl
July 9.80 217.32 5.38 2.00 '-II 0.43 b8dl 2760 1.16 b8dl 3.20 b8dl 4230 0.07 '-II 0.]0 bind 1
Aul '.18 167.16 5.32 1.80 bI8d 1 0.30 bI8d 1 1730 1.48 b8dl 2.56 b8d1 3180 0.20 bI8d 1 0.64 bmdl
Sept 24.77 1007 .)4 5.53 2.22 b8dl 2.24 bI8d 1 8640 5.05 0.11 43.63 0.95 18200 0.06 bI8d 1 1.09 '-II
Oct 5.63 318.31 5.52 2.46 b8dl 0.78 bI8d 1 6430 4.81 0.09 30.93 0.58 9920 2.02 bI8d I 20.04 bald 1
Nov 7.67 421.92 5.40 1.37 bI8d 1 0.58 '-11 3]70 1.84 b8dl 6.20 bI8d 1 5200 1.36 '-II 7.07 bald 1
Dec 3.09 7.)4 5.34 1.34 bI8d 1 0.01 bI8d 1 1730 1.04 b8dl 1.80 b8dl 1830 0.5] '-II 0.97 bmdl
. dlmi. control drein line ve. not in.talled until the .iddle of Augu.t.
b pvnd. roc.-' ve. not detenoined on the.e ...,le..
c Thia val... repre.ent. only one half the 8Onth.
d nenf. no ....le va. taken due to neglilible flow.
e trece. diacher.e va1uu _ra 1e.. thaD 0.01 kg of N03-N and '04-P.
f b8dl. concentration ve. belO11 the .inl- detection level. Mln!- detection levelo for NO]-N and P04-' are 0.04 ppm and 0.06 ppm, re.pectively.
Dt.lcharp valu.. for concentration lower than these level. were not calculated.
-------
Total annual quantities of rainfall, irrigation, drainage, surface runoff,
piration, N03-N discharged in drainage and runoff, and P04-P discharged in
for ST, DT and DTl soil management plots during 19734 1974 and 1975.
1973 197'
DT DTl ST DT DTl
1311:""64 13G4 1211:""85 1211:""85 1205
20.58 20.58 38.66 38.66 38.66
Table 13.
Rainfall (em)
Irrigation (em)
Rainfall + Irrigation
(em)
Drainage (em)
Surface Runoff (em)
Drainage + Runoff (em)
Estimated Evapotrans-
piration" (em)
N03-N discharged in
drainage (kg/ha)
N03-N discharged in
runoff (kg/ha)
Total N03-N discharged
(kg/ha)
Percentage N03-N
discharged (%)
P04-P discharged in
drainage (kg/ha)
P04-P discharged in
runoff (kg/ha)
Total P04-P discharged
(kg/ha)
Percentage P04-P
discharged (%)
ST
1311:""64
20.58
155.22
83.31
0.30
83.61
71.61
31. 75
0.02
31.77
18.74
3.75
<
3.76
20.29
155.22
58.50
9.90
68.40
86.82
10.36
0.32
10.68
6.30
0.68
.01
0.10
155.22
29.69
12.20
41.89
113.33
7.97
1. 16
9.13
5.38
0.33
0.16
0.49
2.66
163.51
84.95
0.17
85.12
78.39
35.30
< 0.01
35.31
20.82
< 0.01
3.15
16.99
163.51
43.83
9.68
53.51
110.00
3.14
0.70
0.37
163.51
30.61
8.89
39.50
124.01
3.74
0.69
13.34
0.82
ST
l1b.'"37
29.66
146.03
64.72
0.23
64.95
81.08
45.77
45.79
27.01
13.42
estimated evapotrans'
drainage and runoff
1975
DT
llb.'"37
29.66
146.03
26.46
4.42
30.88
115.15
0.02
2.47
0.01
2.48
DTl
l1G7
29.66
146.03
19.49
6.60
26.09
119.94
0.36
3.65
0.44
0.78
4.22
5.79
4.43
2.61
14.16
8.35
0.25
0.61
4.09
2.41
0.86
1. 07
0.32
1.18
0.36
0.01
0.04
6.38
0.15
0.16
0.23
0.27
1.46
0.86
*Evapotranspiration was calculated by subtracting total quantities of drainage and surface runoff from
the total quantities of rainfall and irrigation. The water balance components of deep seepage and
soil water storage were assumed negl igibly small and were thus ignored for these calculations.
41
-------
Table 14:
Total annual quantities of rainfall, irrigation, drain-
age, estimated evapotranspiration, N03-N discharged in
drainage, and P04-P discharged in drainage for the Con-
trol soil management plot during 1973-1975.
1973 1974 1975
Ra i n fall (cm) 134.64 124.85 116.37
Irrigation (cm) 0 0 0
Ra i n fa 1 1 plus Irrigation (em) 134.64 124.85 116.37
Drainage (cm) 37.75 66.05 46.03
Estimated Evapotranspiration* (cm) 117047 970 LI6 100.00
NOrtJ discharged (kg/ha) 0.90 2095 12.30
Percentage N03-N discharged (%) 0053 1. 74 7.26
P04-P discharged (kg/ha) 0.82 0.97 0051
Percentage P04-P discharged (%) 4044 5.25 0.81
.'-
"Evapotranspiration was calculated by subtracting total quantities
of drainage from the total quantities of rainfall. The water
balance components of deep seepage, surface runoff, and soil
water storage were assumed negligibly small and were thus ignored
for these calculationso
42
-------
........, 6 (1975) (1973) (1974)
~
..c:
-
C»
.¥
.........
-0
Q)
C»
L 4
CU
..c:
u
CI} ST plot
o
CL
I
a 2
CL .r: DTL plot
CU --- :----- .J4ILDT plot
+-' ---
~ '\...... Control
--- plot
o ~
145 150 155 160 165
Total Rainfall and Irrigation (em)
FIGURE 11.
Total P04-P discharged annually with surface and subsurface
drainage water versus total amounts of rainfall plus irri-
gation for ST, DT, DTL, and Control soil management plots
for the period 1973-1975.
43
-------
plot except for the 1974 data when the N03-N discharge decreased. Magnitudes
were generally similar for N03-N and P04-P losses from the deep-tilled plots.
Discharge of N03-N decreased slightly with increasing rainfall plus irriga-
tion for ST, but discharges of P04-P increased slightly with increasing rain-
fall plus irrigation. Nitrate losses were always many-fold greater for ST
than either DT or DTL plots. Discharge of P04-P from the Control plot
(Table 14) generally had the same magnitude as that for the deep-tilled plots.
Losses of nitrate, from the Control, however, were greater than DT or DTL
in 1975 but were considerably less during 1973 and 1974.
Expressing the annual losses of N03-N in both surface and subsurface
drainage as percentages of N applied, N03-N discharged from the ST plot
accounted (Table 13) for 18.74% in 1973, 20.82% in 1974, and 27.01% in 1975.
For DTL comparable values were 5.38% in 1973, 8.35% in 1974, and 2.41% in
1975. Comparable values for DT were 6.30% in 1973, 2.61% in 1974, and 0.36%
in 1975. Thus average losses of N03-N over the 3-year period were 22.2% for
ST, 5.4% for DTL, and 3.1% for DT. These values are less than the values
of 31.9% for ST, 15.0% for DTL, and 8.3% for DT obtained during 1971-1972
by Calvert (1975). For a six-month period during 1971, Calvert and Phung
(1971) obtained % N losses of 35.4% for ST, 16.7% for DTL, and 8.7% for
DT. Higher N losses obtained during 1971 and 1972 than during 1973-1975
may be partially due to less uptake of N by the smaller and younger citrus
trees. Calvert and Phung (1971) attributed the greater N loss from DTL
relative to that from DT to greater rates of nitrification due to the bene-
ficial effect of lime on soil microorganisms.
Annual losses of P04-P with surface and subsurface drainage during 1973,
1974, and 1975 were 3.76, 3.15, and 2.48% for ST; 0.49, 1.18, and 0.27%
for DTL; and 0.78, 1.07, and 0.16% for DT. Thus average losses of P04-P
over the 3-year period were 3.13% for ST, 0.65% for DTL, and 0.67% for DT.
These percentages are in the same order of magnitude but less than the values
of 14.2% for ST, 2.0% for DTL, and 3.4% for DT obtained during 1971-1972 by
Calvert (1975). The unfertilized Control plot produced P04-P losses which
were of the same order as the fertilized DT or DTL treatments in all three
years of the study.
Percentage losses of N03-N and P04-P in the Central Sump (sampl ing site
7)and South Sump (sampl ing site 8) outflow water was calculated based on the
amount of fertilizer applied to the nine citrus plots (9 ha) comprising the
entire SWAP citrus grove in each of the three years in the study (Table 15).
In 1973 losses of N03-N from the Central and South Sumps both approximated
10.4% of that applied to the nine citrus plots. Loss of P04-P was calcu-
lated to be 5.7% from the Central Sump and 10.1% from the South Sump in
1973. The 1974 data show that N03-N percentage losses from the Central
Sump and the South Sump were very close with 14.0% lost from the Central
Sump and 14.2% lost from the South Sump. Approximately 5.0% of the P04-P
was accounted for as a loss from the Central Sump in 1974 and 12.0% was
calculated to be lost from the South Sump in 1974. In 1975 loss of N03-N
and P04-P was much less with only 8.0% of the N03-N appearing at the Central
Sump and only 3.0% accounted for at the South Sump. P04-P losses amounted
to only 1.2% at the Central Sump and 0.07% at the South Sump in 1975.
44
-------
Table 15:
Total annual quantities of rainfall plus irrigation, water, N03-N, and P04-P dis-
charged from the Central Sump and South Sump of the SWAP citrus gr0ve during 1973,
1974, and 1975.
1973 1974 1975
Central South Central South Central South
Sump Sump Sump Sump Sump Sump
~ Rainfall plus Irrigation 155.22 155.22 163.51 163.51 146.03 146.03
\J1 (H3/ha x 102)
Wa t e r discharged (H3/ha x 102) 649.50 1,249.11 532.70 1 ,084.66 485040 81 1 0 00
NO -tJ d i scha rged (kg/ha) 158.38 158.22 214.36 216.95 122.13 46.49
3
P04-tJ d i scha rged (kg/ha) 9046 16.84 8.38 19.98 1.94 0011
-------
During 1973 and 1974 the amount of N03-N lost in the Central Sump
water was approximately the same as the amount lost from the South Sump.
Furthermore, the concentration of N03-N in the Central Sump was approximately
twice that in the South Sump while the amount of flow from the South Sump
was about twice that from the Central Sump, thus accounting for the almost
equal losses of N03-N from both sites. Without more intensive investigation,
it is not possible to say whether these figures are merely coincidences or
whether the bulk of the N03-N showing up at the South Sump was in fact the
same N03-N which originated at the Central Sump. Furthermore, in 1975, a
year of reduced drainage flow, the amount of N03-N lost from the Central
Sump approximated 8.0% as compared to only 3.0% loss of N03-N from the
South Sump. This difference might be explained by the fact that the water
was recycled for irrigation use more in this drier year, and because of
fewer rainfall events the water remained in the perimeter ditch system for
the grove much longer before flowing out and, therefore, considerably more
time was available for denitrification to occur and the chance that N03-N
was absorbed by ditch vegetation was considerably greater.
The percentage loss of P04-P was about twice as high from the South
Sump as from the Central Sump in 1973 and 1974, but in 1975 losses from
both Sumps were almost nil (only 1.2% from the Central Sump and 0.07% from
the South Sump). The same reasons given for reduced loss of N03-N in 1975
also apply here. In 1975, there was a much greater chance for P04-P to be
removed in the perimeter ditch system in both biological and chemical sinks
which fix P04-P.
As stated earlier, it is not known for certain whether the close corre-
spondence of losses of N03-N from the Central and South Sumps in 1973 and
1974 is coincidental or not, but it is presumed that the balance of nutrients
in the perimeter ditch system surrounding the SWAP area is fairly complex.
That is, the P04-P and N03-N concentration and discharge at the South Sump
is an integrated summation of inputs, such as subsurface drains, surface
runoff from the plot areas, surface runoff from the non-agricultural area
(largely vacant land) seepage from this area and from adjoining areas into
the ditch system, fixation of N03-N in rainfall from thunderstorms and
nutrient content of irrigation water. Both well water and water brought
in from the North Saint Lucie River Water Management District are used for
irrigation of the SWAP experimental grove. These are only a few of the pos-
sible reasons for observed increases as well as decreases in nutrient con-
centrations between the Central Sump and the South Sump in the SWAP experi-
mental grove. All of these possibilities should be investigated before an
exact nutrient balance at this location can be obtained. However, a loss
of approximately 10% of the N03-N appl ied as fertilizer would not be con-
sidered an excessive loss, especially when it is possible that part of the
N03-N originated from sources other than appl ied fertilizer.
,Monthly values of subsurface drainage were found to be linearly related
(Figs. 12, 13, and 14) with monthly totals of rainfall plus irrigation for
the 3~year period for each soil treatment. Linear regression equations
(Table 16) were least-square fitted to the data for the three treatments.
The slopes of these equations were 0.70, 0.35, and 0.25 for ST, DT, and
DTL plots, respectively. These slopes show that for a given monthly input
46
-------
E
-S
Q)
0)
OJ 20
c
OJ
L
o
Q)
u
OJ
't 10
::I
111
.Q
::I
l!)
E
-S
Q)
0)
OJ 20
c
OJ
L
o
Q)
u
OJ
't 10
::I
111
.Q
::I
(j)
ST PLOT
~
,
,
..-
,
,
..-
..-
>'
...'
...'
...'
~~'
...
..-
..-
..-
,
,
..-
...
..-
,
,
,
...
...
,
,
~'
,
,
,
,
,
, II>
..-
..-
..-
..-
,...' .
,
,
, 0
,
...",/
o ...'"
o
30
01973
81974
. 1975
o
.
Q
35
8
o
8
o
10 15 20 25
Total Monthly Rainfall and Irrigation (em)
30
FIGURE 12.
Monthly amounts of subsurface drainage plotted versus
amounts of rainfall plus irrigation for the ST soil treat-
ment during the period 1973-1975. The dotted line has a
zero intercept and a unit slope, and the sol id line was
obtained using linear regression. The regression equation
is presented in Table 16.
30
DT PLOT
01973
011974
. 1975
...
...
...
--
...
/
--...'"
,
...
......'
...
...
...
...
-'"
...'"
/
,
...
.../
,
...
...
/
~
~/
/
...'"
,
,
~
...
/
/
,
/
/
/
/
..-
/
/
/
,
..-
--
--
--
...
,."" 0
o ...--
o
o
8
o
Ii>
00
8
o
.
o
FIGURE 13.
5 10 15 20 25
Total Monthly Rainfall and Irrigation (em)
Monthly amounts of subsurface drainage plotted versus rain-
fall plus irrigation for the DT plot during the period 1973- \
1975. The dotted 1 ine has a zero intercept and a unit slope,
and the sol id 1 ine was obtained using linear regression.
The regression equation is presented in Table 16.
1~7
30
35
-------
E
~
01
<11
c
<11 20
L
o
u
<11
'+-
L
~ 10
.D
:J
Lf)
DTL PLOT
;-
/'
--
--
--
--
...-
--
/'
/'
...-
/'
...-
;-
--
--
...-
--
...-
...-
...-
--
...-
...-
...-
...-
...-
...-
--
--
--
...-
...-
/'
/'
...-
...-
...-
...-
...-
...-
...-
...-
--
/'
/'
...-
...-
/'
--
...-
--
;-
o --
o
30
'" 1973
111974
. 1975
II
'"
e
II
'"
35
30
10 15 20 25
Total Monthly Rainfall and Irrigation (em)
FIGURE 14.
Monthly amounts of subsurface drainage plotted versus rain-
fall plus irrigation for the DTL plot during the period
1973-1975. The dotted 1 ine has a zero intercept and a unit
slope, and the solid 1 ine was obtained using 1 inear regres-
sion. The regression equation is presented in Table 16.
Table 16:
Linear regress'ion equations relating D, monthly subsur-
face drainage (em), and I, monthly rainfall plus irriga-
tion (cm), for 5T, DT and DTL plots for the period 1973,
1974 and 1975.
.k ,t~..}: ;";~";,,
50i 1 Treatment R-5quare CoVo 10
(%) (%) (em)
5T D = -2065 + 0070 I 85.68 36.05 3.8
DT D = -0.96 + 0.35 I 57039 68003 2.7
DTL D = 1005 + 0.25 I 72.63 56.38 4. 1
.~
"R-5quare is the regression coefficient squaredo
..'......1..
""CV is the coefficient of variationo
..'....'.....'...
"""10 is the value of I corresponding to D = O.
43
-------
of rainfall plus irrigation, the amount of monthly drainage from
approximately twice that for DT. Drainage from DTL was slightly
than from DT. These findings confirm drainage results presented
in this report.
ST was
less
earl ier
Estimates of N, P, and K removal in oranges are presented in Table 17
for the 3 soil treatments. Using average fruit yields from 1975 and nut-
rient contents of fruit by Reitz (1961), N removal was calculated to be
Table 17:
Average fruit yields of Pineapple Orange growing
in ST, DT, and DTL treatment plots during 1975-
1976 and calculated amounts of N, P, and K in the
harvested fruit. Calculations were based upon
the publication of Reitz (1961) who stated that
1000 boxes (90 lbs per box) of oranges contain
179.20 kg of N, 22.48 kg of P, and 269.62 kg of K.
Soil Fruit N P K
Treatment Yield Removal Removal Removal
(boxes/ha) (kg/ha) (kg/ha) (kg/ha)
ST 167 29.9 3.8 45.0
DT 156 28.0 3.5 42. 1
DTL 216 38.7 4.9 58.2
29.9, 28.0, and 38.7 kg/ha for ST, DT, and DTL plots. Removal of P was
calculated to be 3.8, 3.5, and 4.9 kg/ha for ST, DT, and DTL. Expressing
these nutrient removals as percentages of fertilizer applied (169.52 kg/ha
of Nand 18.48 kg/ha of p), N removal by fruit in ST, DT and DTL plots was
20.6, 18.9, and 26.5%. Thus the sums of the percentages of N discharged
with surface and subsurface drainage and N removed with fruit for ST, DT
and DTL plots are 39.8, 19.6, and 28.2%. Comparable percentages for P
were 23.7, 19.6, and 27.2% for ST, DT, and DTL. These values indicate
that large percentages of the appl ied Nand P are unaccounted for, i.e.
greater than 60% for N and greater than 70% for P. Individual values are
60:2, 80.4, and 71.8% of the applied N for ST, DT, and DTL, and 76.3, 80.4,
and 72.8% of the applied P for ST, DT, and DTL. The percentage of unrecov-
ered Nand P seems to be highest in the DT plot. The unrecovered N was
probably distributed among uptak~ by the citrus tree and sod; denitrifica-
tion of N03-N to the gaseous state, adsorption of NH4-N to the soil
49
-------
colloids, precipitation as iron and aluminum phosphates, and P in the soil
solution. The relatively large percentages of Nand P not recovered as
surface and subsurface drainage loss and removal by citrus fruit seem to
suggest that the content of these nutrients in the soil at any given time
may be rather large. The exact fate of the unrecovered Nand P can not be
determined at this time.
Intensive 5tudies Of Nutrient Leaching
Four short-term, intensive studies on N03-N and P04-P discharge losses
in both surface and subsurface drainage water from ST, OT, and OTL tillage
systems were conducted in March and May of 1974, and in February and March
of 1975. These studies were conducted during the drier months of these
years so that the water input (irrigation) could be controlled more preci-
sely. Losses were examined over 14-day intervals that followed irrigations
of 16.0, 8.2, 5.7 and 2.4 cm of water. Fertilizer amounting to 530 kg per
ha of an 8-2-8 mixture (42 kg/ha nitrogen as ammonium and nitrate and 50 kg/ha
P04-P as super-phosphate) was applied immediately before turning on the
irrigation system. An exception was the 5.7 cm irrigation period (Febru-
ary 1975) when plots were not fertilized prior to irrigation. Instead,
the preceding fertilization was made three months prior to the 5.7 cm
irrigation.
Concentration, nutrient flux and water flow curves for the four events
are presented in Figs. 15 through 26 for ST, OT, and OTL plots.. Tables 18
through 21 present the same data in numerical form along with values for
water table height, rainfall and time. A summary table composed of means
for each event is presented in Table 22.
A series of smooth N03-N and P04-P concentratiol. and discharge curves
with well defined peaks were obtained from these intensive studies. Exam-
ples of the type of curves obtained by intensive samp1 ing are presented as
Figs. 15, 16, and 17 for subsurface drainage water from ST, OT, and OTL
plots during parts of May and June of 1974 (16.0 cm of irrigation was
applied on May 21, 1974).
Surface-tilled plots gave greater N03-N discharges (Table 22), 14.4
kg/ha N03-N, in the 14-day period after the 16.0 cm irrigation, than either
OT or OTL, which were 0.6 and 5.1 kg/ha N03-N, respectively. Following
the 16-cm irrigation, maximum concentrations of N03-N in the subsurface
drainage of both ST and OTL were much higher (18.4 and 16.8 Wg/m1) than of
OT (2.3 wg/m1). For the 16.0 cm irrigation concentrations of N03-N in
drainage from the ST and OTL plots reached two peaks, one at 2 days and
another at 13 days (Figs. 15 and 17); however, only one peak at 2 days
was observed for the OT plot. Nutrient discharges from ST were usually
greater than from OTL mainly because water discharge was greater. Although
subsurface drainage from the OT plot exceeded that from OTL, N03-N dis-
charges from OTL were higher than from OT, probably because the mixed and
limed soil had a higher nitrification rate, (Phung, 1971). ST plots dis-
charged up to 0.38 kg/ha P04-P in the 14-day period following the 16.0 cm
irrigation, but phosphate discharges from OT and OTL were only 0.07 to 0.11
kg/ha P04-P in the 14-day period, respectively.
50
-------
FIGURE 15.
~
~ 20
Y1
x 10
:J
LL 8 f--- --,
L 6:
Q) 4:
+-' '
ro 2:
~ i
0'
~2
ro 240
~
.922
~10
LL 80
z 60
I
cf40
z 20
o
:2 8
-
ro
..c
----6
.9
x
:J 4
LL
~ 2
O~
0...
00
A
28 "0
Q)
Q.
20 --- ft
12 52
'-'ro
~
5T Treatment
16.0cm Irrigation
4
~
c
18 :8
ro
14 ~
12 --- ~
10 E ~
8 'Q)8
6 ~z
'-' I
4 Or<)
2 Z
o c
o
ro
L
+-'
---C
to E ~
18--c
6 ~8
4'-'0...
. I
2 a
o 0...
o Concentrat ion
. Flux
o Concentration
. Flux
2
4
6 8 10
Time (days)
12
14
Fluxes of drainage water, N03-N, and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment during a l4-day period (March 6-19,
1974) fol lowing l6.0-cm irrigation. Water was appl ied con-
tinuously over a 39-hour period immediately after a quart-
erly appl ication of 530 kg/ha of an 8-2-8 fertil izer. Rain-
fall occurred on days 9 and 10 for a total of 2.4 cm.
51
-------
FIGURE 16.
~ ~ 10
- ~8 ,un_-,
LLro : :
L .s:::. 6: :
(\)~4 !
+' E '
ro '-" 2 !
~ :
o
X
:J ~100
LL--=E..80
ro
z..c 60
1----
0.9 40
z 20
o
8
x ~ 6
:J ..c
- ---
LL ro 4
..c
---
a... 0>
1:<1" '-" 2
o
a...
00
DT Treatment
16.0 cm Irrigation
"0
.~
~ ~
2 E ~
8..!:t1ij
4 ~
o c
o
~
+'
C
(\)
O~~
8Eo
6 ........U
o>Z
43(5)
2 Z
o c
o
+'
ro
L.
+-'
C
.O~ ~
.8~8
60>U
:4~
. I
.2 O"'t
o a...
o Concent rat ion
. Flux
o Concentration
. Flux
2
6 8 10
Tim e(days)
12
14
4
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DT soil
management treatment during a 14-day period (March 6-19,
1974) following a 16.0-cm irrigation. Water was appl ied
continuously over a 39-hour period immediately after a
quarterly application of 530 kg/ha of an 8-2-8 fertil izer.
Rainfall occurred on days 9 and 10 for total of 2.4 cm.
)2
-------
>( ~ 1
:J..f:..
LLCU
.c
L~
.$$
~.
DT L Treatment
16.0cm Irrigation
r-----
I
I
I
5 :
I
, !
o !
~ 100
-.......
LL~ 80
z~ 60
~--4
~-92
o
8
6
o Concentration
. Flux
>( ~
~ ..c 4
LL-
cu
q- ~2
O"t -9
a...
o Concentration
. Flux
o
o
6 8 10
T i me(days)
2
4
12
14
"0
20 ~
6 a.
12~~
E L
8~$
4 ~
o
5
0....... ~
EO
--u
5 OIZ
3cr
z
o
.0 ~
Q8~ 0
.6EU
-- a...
4011
.23.0"t
o a...
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DTL soil
management treatment during a 14-day period (March 6-19,
1974) following a 16.0-cm irrigation. Water was appl ied
continuously over a 39-hour period immediately after a
quarterly appl ication of 530 kg/ha of an 8-2-8 fertil izer.
Rainfall occurred on days 9 and 10 for a total of 2.4 cm.
FIG UR E 1 7 .
53
-------
FIGURE 18.
i- ......
if-. 12 ST Treatment .E
"0
~ 8.2 cm Irrigation 10 .~
::J 8 8:
i:L 8 ,n,
, ,
0> 2-
)(10 0 u
::J C
i:L 80 0
u
60 5
~ 40 z
c) 20 1("')
o
Z 0 0 z
...... 8
~ 0 Concentration --l
('(!
~ 6 . Flux 0>
'-" 1.0 ~
)(
::J 4 .8 u
LL c
.6 8
a...
I 2 .4 a...
O~ I
.2 O~
a... 0 0 a...
o 2 4 6 8 10 12 14
Ti me(days)
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the 5T soil
management treatment during a 14-day period (May 21 through
June 3, 1974) following a 8.2-cm irrigation. Water was
appl ied continuously over a 20-hour period immediately after
a quarterly appl ication of 530 kg/ha of an 8-2-8 fertilizer.
Rainfall occurred on days 13 and 14 for a total of 2.7 cm.
54
-------
FIGURE 19.
~ 10
LL- 2 8 rn,
---- I I
.::-... "
L ro 6 : :
£ ,I
Q)~~4::
+-' ' ,
en : :
~~ 2 ! !
o I
x .
:J ,.... 100
LL~80
z~ 60
~~4
~ '-' 20
o
x
~,.... to
LL~O
Q.. ro 06
,£
O't0>04
Q.. '-' Q2
00
2
DT Treatment
8.2 cm Irrigation
1)
Q)
o Q.
8,....~
6 E ~
4 u+-'
'-'ro
2 ~
o c
o
5 :g
L
+-'
,....c
10 E ~
-...........c
0)0
5 a-~
'("I)
o
o z
c
.Q
~
o Concentration
. Flux
o Concentration
. Flux
+-'
10 ~
u
8~ c
E 0
.6...........u
401Q..
.22-6't
o Q..
4
6 8 10
Ti me (days)
14
12
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DT soil
management treatment during a 14-day period (May 21 through
June 3, 1974) following a 8.2-cm irrigation. Water was
appl ied continuously over a 20-hour period immediately after
a quarterly appl ication of 530 kg/ha of an 8-2-8 fertilizer.
Rainfall occurred on days 13 and 14 for a total of 2.7 cm.
55
-------
FIGURE 20.
DTL Treatment
8.2 cm Irrigation
x 10
:J""""
_..c:
lJ...--
cu
L..c:
<1>;;)-
"tUE
~'""'
r---,
. .
: I
5 : :
I ,
, ,
, ,
, I
: I
, I
, ,
o I 0
.R.
~ ........1
-..c:
lJ...--
cu
Z..c: 50
,--
cfOJ
Z'""'
o
x 1.
:J........
-..c:
lJ...-
9-~05
~-
OOJ
0...'""'
o
o
2
4
~
o Concentration
. Flux
o Concentration
. Flux
6 8 10
T i me(days)
12
14
T
iJ
<1>
o :=
8 8:
6
-------
FIGURE 21.
"0
ST Treatment 6 n>
x", 10 2.4 cm Irrigation Q.
Q.
::J.c 4 ,,
~M-- 4 " 2 ~n;
" ~
...... E 2 "
"
cu........ "
I'
3: 0 " .~
" 0
o Concentration ~
......
. Flux c
n>
o u
c
8,,0
-u
6~z
4 011("")
2 2-~
o
0 Concentrat ion
x . Flux
::J"
LL ~ 1.0
~ OB
'T -0;-- 0.6
O~ 0.4
CL 0.2
00 2 4 6 8 10 12 14
T i me(days)
Fluxes of drainage water, N03-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the ST soil
management treatment during a 14-day period (March 17-30,
1975) fo1 lowing a 2.4-cm irrigation. Water was app1 ied
continuously over a 6-hour period immediately after a quart-
erly app1 ication of 530 kg/ha of an 8-2-8 fertilizer. Rain-
fall occurred on days 2 and 3 for a total of 2.9 em.
57
-------
6 "U
Q)
x 10 DT Treatment
:J- 2.4cm Irrigation Q.
-..c 8 4 Q.
LL --- «
OJ 6 -
L..c E L
(l)M"- 4 n . 2 u$
11jE ,. I
,. I -OJ
2 I, I
~- " I ~
I,
0 " 0
15
~_100 0 Concentration 0 u
. Flux c
-..c -0
LL-- EU
OJ
z..c 50 5--z
(f-;;; 0') I
30
z- 0 z
o
o 2 4 6 8 10 12 14
T i me(days)
FIGURE 22.
Fluxes in drainage water and N03-N and concentrations of
N03-N in subsurface drainage from the DT soil management
treatment during a 14-day period (March 17-30, 1975) fol-
lowing a 2.4-cm irrigation. Water was app1 ied continuously
over a 6-hour period immed iate1y after a quarterly app1 ica-
tion of 530 kg/ha of an 8-2-8 ferti1 izer. Rainfall occurred
on days 2 and 3 for a total of 2.9 cm. Concentrations of
fluxes of P04-P were very small and are not shown on the
figure.
53
-------
"D
Q)
Q.
n
«
>< DTL Treatment
:J 10
-~ 2.4 em Irrigation
LL..c
---
L OJ 5
Q)..c n
+-1M- t
" I
OJ E II
" I
~~ 'I I
0 " !
~ 100
-~
LL..c
---
OJ
Z ..c 50
I (Y) ---
00)
z~
FIGURE 23.
~L
2 E 2
u OJ
o ~~
15
o Coneentrat ion
. Flux
u
10 c
~o
EU
"'-z
5~()
z
o
o
o
6 8 10
T i me(days)
2
12
14
4
Fluxes of drainage water and N03-N and concentrations of N03-N
in subsurface drainage from the DTL soil management treat-
ment during a 14-day period (March 17-30, 1975) following a
2.4-cm irrigation. Water was appl ied continuously over a
6-hour period immediately after a quarterly appl ication of
530 kg/ha of an 8-2~8 fertil izer. Rainfall occurred on days
2 and 3 for a total of 2.9 cm. Concentrations and fluxes
of P04-P were very small and are not shown on the figure.
59
-------
FIGURE 24.
t
M-1
~1
.2 8
LL 6
L
4
cu 2
~ 0
,.....,
.c
-
cu
~
9120
><
~
LL 80
Z
I 40
cJ1
~ 0
--=E..
cu 24
.c
dJ
x 2.
~
i:L 08
'7- 04
0'<1"
£l.. 0
o
,-,
I I
"
, I
, J
, I
, I
"
J I
A
\
'E
~
o~
88:
6
-------
FIGURE 25.
"'0
o ~
8 8:
«
6.......L
4 E2
2~C1I
o 3
x 1
~2 8
LL---
LC1I 6
Q)-'= 4
+'~
~-!; 2
o
DT Treatment
5.7 cm Irrigation
n
I I
I I
I I
I :
I I
I I
I I
t
I
f :
I I
I I
x
~ 1
LL :c 80
--
Z C1I 60
'-'=
0'-40
2.9 20
o
o Concentration
. Flux
o u
8 5
6'Eu
4 '-...2
OI~
2 ..?- u
o 2
X
::J....... to
LL~OB
CL C1I 0.6
,-'=
O~-;; 0.4
CL '-' Q2
00
o Concentration
. Flux
.0
6 8 10
Time(days)
12
14
2
4
Fluxes of drainage water, N01-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DT soil
management treatment during a 14-day period (February 11-24,
1975) following a 5.7-cm irrigation. Water was appl ied
continuously over a 14-hour period which occurred three
months after a quarterly appl ication of 530 kg/ha of an 8-2-8
fertil izer. Rainfall occurred on days 11 and 13 for a total
of 8.6 em.
61
-------
FIGURE 26.
10 ~
8 8:
6 < 1
:J,....,
LL~
,-co 5
Q)~
1ii'E
~'"' 0
DTL Treatment
5.7 cm Irrigation
,...,
I I
I I
I .
I .
I .
~ I
I .
.
I
1 I
: '
~ 1
iL2
-.......
Zco5
~
z'"'
o
o Concentration
. Flux
10 ~
o
~u
5--tz
016'
3z
o
~ 1.0
-2
LL'-.
a.. ~ 05
I :-...
aVOI
0..'"'
o
o
o Concentration
. Flux
.0
2
6 8 10
Ti me(days)
4
12
14
Fluxes of drainage water, N01-N and P04-P and concentrations
of N03-N and P04-P in subsurface drainage from the DTL soil
management treatment during a 14-day period (February 11-24,
1975) following a 5.7-cm irrigation. Water was app1 ied
continuously over a 14-hour period which occurred three
months after a quarterly app1 ication of 530 kg/ha of an 8-2-8
ferti1 izer. Rainfall occurred on days 11 and 13 for a total
of 8.6 em.
62
-------
Table 18. Concen t ra t ion and flux of N03-N and P04-P in subsurface drainage water from 5T, DT,
and DTL treatments during a 14-day pe r i od (March 6-19, 1974) fo 11 ow i ng a 16-cm
i r r i ga t ion. The plots were irrigated continuously over a 39-hour per i od immediately
after a quarterly appl ication of 530 kg/ha of an 8-2-8 fertilizer. Rainfall a 1 so
occurred on days 9 and 10. Water table height (W.T. ht.) are presented.
- - Surface Tilled Deep Ti 11ed Deep Tilled Limed
Rain Flow W.T. N03-N P04-P N03-N P04-P Flow W.T. N03-N P04-P N03-N P04-P Flow I,.T. NOrN P04-P N03-N P04-P
~ Time !ill Rate Ht. Cone. Cone. Flux Flux Rate Ht. Cone. Cone. Flux Flux Rate Ht. Cone. Cone. Flux Flux
cm ab -m- -ppm - - g/ha/hr- a -m- - ppm - - g/ha/hr- a -m- - ppm - -~/ha/hr-
Oa 0.00 5.09 1. 78 bmd1c bmd1 bmd1 0.00 5.19 bmd1 bmd1 bmd1 bmd1 0.00 5.31 1.35 bmdl bmdl hmd1
1 0500 0.00 1.15 5.98 2.10 0.08 2.42 0.09 0.17 6.12 0.12 0.06 0.02 0.01 0.08 6.26 1.87 0.14 0.15 0.01
0800 3.77 3.50 0.13 13.20 0.49 0.48 0.13 0.07 0.06 0.03 0.78 2.50 0.16 1. 95 0.12
1000 6.59 8.40 0.15 55.35 0.99 0.87 0.15 0.08 0.13 0.07 0.85 5.00 0.43 4.25 0.36
1200 7.00 10.00 0.20 70.00 1.40 1. 26 0.17 0.09 0.21 0.11 0.92 7.60 0.34 6.99 0.39
1400 8.00 11.40 0.22 91. 20 1. 76 1.65 0.20 0.10 0.33 0.17 1.51 10.80 0.28 16.31 0.42
1600 8.76 12.80 0.23 112.13 2.01 2.05 0.25 0.12 0.51 0.25 2.10 13.70 0.24 28.77 0.63
1800 9.71 13.60 0.28 132.06 2.72 2.46 0.30 0.18 0.74 0.44 3.96 12.60 0.20 49.89 0.79
2000 10.66 14.00 0.31 149.24 3.30 2.90 0.35 0.22 1.02 0.64 4.99 12.40 0.19 61.87 0.85
2200 11.73 14.40 0.33 168.91 3.87 3.30 0.38 0.26 1. 25 0.86 5.84 12.00 0.18 70.08 0.93
2400 12.81 14.80 0.35 189.59 4.48 3.84 0.41 0.30 1. 57 1.15 6.69 11. 30 0.18 75.60 1. 20
0400 0.00 15.78 6.3715.75 0.35 251.00 5.50 4.49 6.12 0.60 0.33 2.69 1.48 7.52 6.40 11.10 0.18 83.47 1.40
0600 16.89 16.20 0.36 273.62 6.08 4.84 0.88 0.29 4.26 1.41 7.95 11.00 0.19 87.45 1. 51
1000 20.32 13.00 0.36 264.16 7.32 5.16 1.31 0.23 6.82 1.18 8.78 10.80 0.20 94.82 1. 75
1200 19.75 12.00 0.36 237.00 7.11 5.21 1.50 0.20 7.81 1.04 7.07 10.40 0.22 73.53 1. 55
1600 14.58 11.80 0.37 172.04 5.39 4.63 2.06 0.15 9.54 0.70 5.82 10.20 0.22 59.36 1.31
1800 11. 70 11. 70 0.37 136.89 4.40 4.36 2.30 0.14 10.03 0.61 5.20 10.10 0.23 52.52 1. 20
C"\ 2000 10.51 11.60 0.37 121.92 3.89 3.92 2.13 0.13 8.35 0.53 4.85 10.00 0.23 48.50 1.14
IoN 2400 8.23 11.40 0.37 93.82 3.05 3.31 1.90 0.13 6.29 0.43 3.75 9.80 0.24 36.75 0.90
1200 0.00 6.51 5.7811.50 0.38 74.87 2.47 2.91 5.89 1.60 0.14 4.66 0.40 3.07 6.13 9.40 0.28 28.86 0.86
1800 5.76 11.40 0.38 65.66 2.19 2.57 1.54 0.14 3.96 0.38 2.60 9.26 0.28 24.08 0.73
2400 5.01 11.40 0.39 57.11 1.95 2.29 1.50 0.15 3.44 0.34 2.38 9.00 0.28 21.42 0.66
4 1200 0.00 4.41 5.6511.40 0.39 50.27 1.72 2.02 5.74 1.40 0.15 2.83 0.30 2.11 5.99 8.80 0.28 18.52 0.59
2400 3.81 11.80 0.41 44.96 1.56 1. 76 1.40 0.15 2.46 0.26 1.83 8.60 0.28 15.74 0.51
1200 0.00 3.32 5.5812.20 0.43 40.50 1.43 1.52 5.68 1.40 0.15 2.13 0.23 1.59 5.92 8.40 0.28 13.31 0.44
2400 2.83 12.60 0.40 35.66 1.13 1.28 1.40 0.14 1.79 0.18 1.34 8.80 0.27 11. 79 0.36
1200 0.00 2.53 5.5313.00 0.38 32.89 0.96 1.15 5.63 1.50 0.14 1. 72 0.16 1.18 5.87 9.40 0.26 11.09 0.31
2400 2.23 13.40 0.34 29.88 0.76 1.02 1.60 0.10 1.63 0.10 1.02 9.80 0.25 9.99 0.25
1200 0.00 1.96 5.4713.80 0.32 27.05 0.63 0.95 5.60 1.80 0.11 1.71 0.10 0.93 5.8310.40 0.24 9.67 0.22
2400 1. 70 14.20 0.32 24.14 0.51 0.88 1.60 0.13 1.41 0.11 0.84 11.00 0.23 9.24 0.19
1200 0.00 1.50 5.42 14.40 0.27 21. 60 0.41 0.85 5.57 1.40 0.14 1.18 0.11 0.75 5.80 11.20 0.22 8.40 0.16
2400 1.30 14.80 0.25 19.24 0.33 0.81 1.30 0.15 1.05 0.12 0.66 11.40 0;22 7.52 0.14
9 1200 0.38 1.15 5.38 15.00 0.22 17.25 0.25 0.77 5.53 1.20 0.16 0.92 0.12 0.57 5.77 11.80 0.22 6.73 0.12
2400 1.00 15.40 0.23 15.40 0.23 0.73 1.10 0.16 0.80 0.11 0.48 12.20 0.20 5.85 0.09
10 1200 2.03 1.28 5.34 15.70 0.23 20.09 0.29 0.69 5.69 1.00 0.16 0.69 0.11 0.44 5.7213.00 0.18 5.65 0.08
2400 1.56 16.20 0.22 25.27 0.34 0.66 0.90 0.14 0.59 0.09 0.39 13.60 0.16 5.30 0.05
11 1200 0.00 1.34 5.4016.60 0.20 22.24 0.27 0.71 5.77 0.80 0.13 0.57 0.09 0.37 5.90 14.00 0.14 5.11 0.05
2400 1.13 17.00 0.18 19.21 0.20 0.77 0.75 0.12 0.57 0.08 0.34 14.80 0.13 5.03 0.04
12 1200 0.00 1.11 5.37 17.50 0.16 19.42 0.18 0.79 5.60 0.70 0.11 0.55 0.08 0.33 5.8315.60 0.12 5.07 0.04
2400 1.10 18.00 0.14 19.80 0.15 0.82 0.65 0.10 0.53 0.08 0.31 16.00 0.11 4.96 0.03
13 1200 0.00 0.92 5.35 18.40 0.12 16.93 0.11 0.79 5.53 0.60 0.10 0.47 0.07 0.30 5.7616.80 0.10 4.96 0.03
2400 0.74 17.40 0.08 12.87 0.06 0.77 0.55 0.08 0.42 0.06 0.28 13.60 0.10 3.81 0.02
14 1200 0.00 0.63 5.34 16.20 0.06 10.13 0.04 0.70 5.48 0.50 0.07 0.35 0.05 0.27 5.70 10.60 0.10 2.86 0.02
2400 0.51 15.00 bmd1 7.65 bmd1 0.64 0.40 0.06 0.25 0.04 0.26 8.00 0.10 2.08 0.02
a b~aeUne readings were taken before study on 3/5/74
b m /ha/hr
c bmdl, concentration was below the miniUl.llll detection level. Minimum detection levels for N03-N and P04-P are 0.04 ppm and 0.06 ppm, respectively.
Discharge values for concentration lower than these levels were not calculated.
-------
Table
0"'
-+:-
Concentrations and fluxes of N03-N and P04-P in subsurface drainage water from ST,
DT and DTL treatments during a 14-day period (May 21, 1974 through June 3, 1974)
following an 8.2 cm irrigation. The Dlots were irrigated continuously over
20-hour period immediately after a quarterly application of 530 kg/ha of an
fertilizer. Rainfall occurred on days 13 and 14. Water tableheig!"Jts (W.T.
are presented.
19.
- - Surface Tilled Dug Tilled Dup Ti lIed Limed
~ Flow W.T. M03-N P(l4-P NOJ-N P04-P Flow IL 1. NOJ-N P04-P NOJ-N P04-P Flow \J.T. NO)-N P04-P NO)-N P04-P
~ "me ~ Rate Ht. Cnn.c. COrK:. Flux Flux. Rate He. Cone. Cone. Flux Flul( Rata IH. Cone. Cone. Flux Flux
(lb -f'pm- -8/h8/hJ' - (l -ppm- -g/ha/hr- (l .",- -ppm- -!;/ha/hr-
0' 0.06 5.43 ],'1:1 0.11 0.21 0.01 0.27 5.49 0.40 _I' 0.11 -I 0.01 5." 0.60 _I 0.01 bmdl
1 0400 0.00 0.85 5.36 4.00 0.11 3.42 0.09 0.79 5.48 0.40 _, 0.31 ""'" 0.18 5.58 1.40 """'I 0.25 bmdl
0800 0.89 4.00 0.12 3.42 0.10 0.78 0.40 ""'" 0.31 """I 0.16 1.40 """I 0.22 bmdl
1200 0.85 4.00 0,13 3.42 D.ll 0.17 0.40 bmdl 0.31 bmdl 0.15 1.40 '-II 0.21 bmdl
1600 0.79 4.00 0.15 3.00 0.13 0.76 0.40 ""'" 0.30 _1 0.12 1.39 ""'" 0.17 '-'I
2000 0.69 4.00 0.19 2.90 0.13 0.75 0.40 ...dl 0.30 """I 0,10 1.30 0.07 0.13 0.01
2200 0.63 4.00 0.21 2.60 0,13 0.76 0.40 '-II 0,30 ...dl 0.11 1.20 0.09 0.13 0.01
'2400 0.63 4.00 0.22 2.51 0.14 0.84 0.40 0.06 0.34 0.05 0.11 1.20 0.11 0,13 0.01
0400 0.00 0.92 5.99 4.00 0.23 3.66 0.21 1.17 6.11 0.30 0.07 0.35 0.08 0.34 6.27 1.50 0.16 0.51 0.05
0600 1.80 4.20 0.14 6.20 0.39 1.54 0.40 0.16 0.62 0.25 0.75 1.80 0.11 3.00 0.07
0800 2.42 4.50 0.25 10.89 0.61 2.11 0.50 0.22 1.06 0.46 1.32 4.00 0.07 5.28 0.09
1000 5.10 5.50 0.26 28.05 1.45 2.60 0.60 0.16 1.70 0.40 2.67 5.00 0.07 13.35 0.18
1200 7.45 7.00 0.26 52.15 1.96 3.02 0.70 O.l) 2.11 0.38 3.57 6.00 0.07 21.42 0.25
1400 9.08 7.50 0.27 68.10 2.50 3.50 1.35 0.09 5.00 0.30 4.25 6.60 0.07 27.50 0.30
1600 10.00 8.00 0.27 73.00 2.80 3.31 2.00 0.07 6.62 0.22 4.60 7.00 0.07 32.20 0.32
2000 11.62 9.00 0.30 104.58 3.49 2.72 2.00 0.06 5.44 0.16 3.86 9.00 0.07 34.74 0.27
2400 9.80 10.00 0.30 98.00 2.99 2.33 2.00 0.06 4.66 0.14 2.98 11.74 0.06 35.00 0.18
0400 0.00 7.18 5.82 11.50 0.31 82.57 2.22 2.04 5.91 2.00 0.06 4.08 0.12 2.49 6.05 13.65 0.06 34.00 0.14
0800 5.41 12.50 0.31 67.62 1.68 1.81 2.00 """I 3.62 """I 2.14 15.80 """I 33.50 """I
1200 4.41 13.00 0.30 57.30 1.36 1.66 2.00 """I 3.32 """1 1.86 17.74 """I 33.00 ....1
1600 3.71 12.60 0.29 49.00 1.20 1.52 2.00 """I 3.04 """I 1.66 19.60 """I 32.50 """I
2000 3.33 11.70 0.28 41.50 1.05 1.39 2.00 b",,11 2.78 """'I 1.54 19.40 """I 32.10 """I
2400 3.09 11.00 0.28 33.99 0.87 1.27 2.00 """'I 2.54 ""'" 1.48 19.28 """I 32.00 ""'"
0400 0.00 2.88 5.62 11.70 0.27 33.60 0.77 1.20 5.73 2.00 """I 2.40 '-II 1.41 5.90 21.10 '-II 31.90 '-II
0600 2.70 12.00 0.26 33.60 0.74 1.17 2.00 """'I 2.34 _I 1.36 22.00 ""'" 31.60 """I
1200 2.58 13.00 0.25 33.54 0.65 1.09 2.10 """I 2.29 """I 1.24 25.00 -I n.oo '-'I
1800 2.35 13.40 0.22 31.98 0.55 0.99 2.25 """'I 2.21 """I 1.15 27.50 "'dl 31.20 ....1
2000 2.31 13.80 0.21 31.98 0.52 0.96 2,30 """'I 2.20 '-'I 1.11 28.30 _1 31.10 """"
2400 2.18 14.50 0.20 31.61 0.44 0.93 2.3t1 ""'" 2.20 """'I 1.04 30.00 '-II 31.20 '-II
0800 0.00 2.07 5.54 10.30 0.18 21.13 0.39 0.87 5.66 2.48 """'I 2.12 bmdl 0.99 5.84 27.50 """'I 27.00 "",,I
1200 1.97 10.60 0.18 20.80 0.36 0.84 2.50 bmdl 2.12 """I 0.95 26.31 """'I 25.00 """I
1800 1.81 10.00 0.18 17 .40 0.34 0.80 2.61 ",dl 2.09 -1 0.91 22.00 _I 20.00 """'I
2400 1.67 10.50 0.20 17.50 0.32 0.75 2.66 """I 2.00 bmdl 0.84 17.50 bmdl 14.70 -I
0800 0.00 1.58 5.48 10.60 0.21 16.80 0.31 0.72 5.61 2.50 ...dl 1.85 """I 0.76 5.7817.50 _I 13.00 """'I
1200 1.50 10.60 0.22 15.90 0.34 0.71 2.46 bmdl 1.75 bmdl 0.70 17 .50 -I 12.25 bmdl
1800 1.40 10.51 0.23 15.00 0.31 0.70 2.41 """I 1.68 bmdl 0.65 17.50 '-'I 11.50 bmdl
2400 1.26 10.40 0.24 13.10 0.29 0.67 2.24 _I 1.50 bmdl 0.62 17.50 bmdl 10.85 bmdl
0800 0.00 1.20 5.42 10.67 0.25 12.40 0.26 0." 5.57 2.05 """I 1.38 """I 0.58 5.7) 17.20 ...., 9.90 '-'I
1200 1.12 10.80 0.25 12.09 0.28 0.63 2.00 bmdl 1. 25 ...dl 0.55 17.00 b""'l 9.35 """"
, 1800 1.10 10.80 0.25 11.20 0.23 0.61 1.86 bmdl 1.10 _, 0.53 16.20 hmdl 8.20 """'I
2400 0.98 10.80 0.22 10.58 0.21 0.57 1. 75 bmdl 1.00 _I 0.49 n.50 ",dl 7 .60 bmdl
0800 0.00 0.92 5.39 10.72 0.20 9.70 0.19 0.54 5.53 1.68 bmdl 0.92 hmdl 0.47 5.69 14.55 b""'l 6.80 bmdl
1200 0.90 10.70 0.20 9.63 0.18 0.53 .1.61 bmdl 0.89 bmdl 0.45 14.00 """'I 6.30 bmdl
1800 0.86 10.70 0.18 9.10 0.17 0.51 1.58 bmdl 0.82 bmdl 0.43 13.00 """'I 5.80 _,
2400 0.84 10.70 0.18 8.98 0.15 0.49 1.53 bmdl 0.75 bmdl 0.39 12.00 bmdl 4.68 bmdl
0800 0.00 0.79 5.35 10.15 0.18 7.80 0.15 0.49 5.50 1.32 bmdl 0.69 bmdl 0.36 5.66 10.70 """'I 4.00 bmdl
1200 0.77 9.90 0.18 7.62 0.14 0.49 1. 23 bmdl 0.62 bmdl 0.35 10.00 bmdl 3.50 bmdl
1800 0.74 9.97 0.18 7.38 0.13 0.49 1.12 bmdl 0.57 bmdl 0.31 10.00 bmdl 3.10 bmdl
2400 0.71 10.27 0.18 7.29 0.12 0.49 1.00 bmdl 0.49 bmdl 0.31 10.00 "'dl 3.10 '-'I
10 1200 0.00 0.63 5.34 10.50 0.17 6.60 0.11 0.44 5~47 1.47 bmdl 0.67 bmdl 0.28 5.63 9.50 bmdl 2.60 '-'I
2400 0.57 10.50 0.17 5.98 0.10 0.39 1.63 bmdl 0." bmdl 0.24 8.00 "'dl 1.90 ""1
11 1200 0.00 0.50 5.32 10.05 0.16 5.00 0.08 0.35 5.45 1.80 bmdl 0.63 bmdl 0.22 5.61 7.80 bllldl 1.70 ....1
2400 0.43 9.60 0.15 4.13 0.06 0.36 1.74 bmdl 0.62 bmdl 0.20 7.50 bmdl 1.50 """I
12 1200 0.00 0.43 5.31 9.49 0.14 4.10 0.06 0.33 5.44 1.62 bmdl 0.53 bmdl 0.19 5.59 7.25 ""1 1.20 """'I
2400 0.47 9.36 0.14 4.00 0.06 0.32 1.50 bmdl 0.48 bmdl 0.17 7.00 '-'I 1.10 ....1
13 1200 0." 0.40 5.29 9.20 0.13 3.60 0.05 0.29 5.43 1.44 bmdl 0.42 """I 0.15 5.58 7.00 bodl 1.00 ....1
2400 0.38 9.00 0.13 3.40 0.05 0.67 1.40 """'I 0.94 bmdl 0.13 7.00 bmdl 0.90 ....1
14 1200 2.03 0.34 5.30 9.00 0.12 2.50 0.05 0." 5.56 1.38 bmdl 0.88 bmdl 0.11 5.60 7.00 bmdl 0.90 bmdl
2400 0.30 9.00 0.11 2.50 0.04 0.62 1.32 bmdl 0.82 ""1 0.10 7 .00 '-'I 0.70 ....1
. baseline readings were taken before study on 5/19/74
mJ/ha/hr
, bmdl, concentration was below the minimum detection level. MinUDum detection levels for N03-N and POi.-P an 0.04 pprn and 0.06 ppm, rupectivelv.
Discharge values for concentrations lower than these levels were not calculated.
a
8-2-8
ht.)
-------
Tab I e 20. Concentrations and fluxes of N03-N and P04-P in subsurface drainage wa t e r from ST,
DT, and DTL treatments du ring a 14-day pe r i od (March 17-30, 1975) after a 2.4 cm irriga-
tion. The plots were irrigated continuously over a 6-hours pe r i od immediately
following a quarterly appl ication of 530 kg/ha of an 8-2-8 fertilizer. Rainfall
occurred on days 2 and 3. Water table height (W.T. ht.) are presented.
- - Surface Tilled Deep Ti lIed Deep Tilled Limed
Rain Flow W.T. N03-N P04-P N03-N P04-P Flow W.T. N03-N P04 -P N03-N P04 -P Flow W.T. N03-N P04-P N03-N P04-P
~ Time fall Rate lit. Cone. Cone. Flux Flux Rate lit. Cone. Cone. Flux Flux Rate lit. Cone. Cone. Flux Flux
cm ab -m- - ppm - _g/ha/hr - a -m- b.;dlpm b;;;d'l -g/ha/hr - a -m- - ppm - -g/hs/hr-
oa 0.00 0.00 5.19 0.30 0.10 0.00 0.00 0.00 5.34 0.00 bmdl 0.00 5.47 0.06 bmdl 0.00 bmd1
1 1400 0.00 0.00 5.20 0.47 0.12 0.00 0.00 0.00 5.47 0.04 bmdl 0.00 bmdl 0.02 5.48 0.09 bmd1 0.00 bmd1
1800 0.11 0.55 0.14 0.06 0.02 0.13 0.06 bmdl 0.01 bmdl 0.02 0.09 bmdl 0.00 bmd1
2000 0.31 0.70 0.16 0.22 0.05 0.16 0.08 bmd1 0.01 bmd1 0.02 0.09 bmd1 0.00 bmd1
2200 0.47 0.90 0.18 0.42 0.08 0.19 0.07 bmdl 0.01 bmdl 0.02 0.09 bmd1 0.00 bmd1
2400 0.57 1.20 0.20 0.68 0.11 0.22 0.07 bmdl 0.02 bmdl 0.03 0.09 bmdl 0.00 bmd1
0300 0.64 0.59 5.24 1.45 0.17 0.86 0.10 0.27 5.56 0.05 bmd1 0.01 bmdl 0.03 5.59 0.09 bmd1 0.00 bmd1
0600 0.60 1.65 0.15 0.99 0.09 0.33 0.05 bmd1 0.02 bmd1 0.03 0.09 bmdl 0.00 bmdl
1200 0.65 2.00 0.10 1.40 0.07 0.41 0.07 bmdl 0.03 bmdl 0.04 0.09 bmd1 0.00 bmd1
1600 0.72 2.15 0.09 1.55 0.06 0.45 0.05 bmdl 0.02 bmdl 0.04 0.08 bmd1 0.00 bmd1
1800 0.75 2.30 0.09 1. 75 0.07 0.45 0.05 bmdl 0.02 bmdl 0.05 0.07 bmdl 0.00 bmdl
2000 0.77 2.40 0.09 1.85 0.07 0.45 0.05 bmdl 0.02 bmdl 0.05 0.06 bmdl 0.00 bmd1
2400 0.82 2.50 0.09 2.05 0.07 0.45 0.05 bmd1 0.02 bmdl 0.05 0.05 bmd1 0.00 bmd1
3 0400 2.29 1.20 5.46 2.59 0.09 3.10 0.10 0.45 5.77 0.05 bmdl 0.02 bmdl 0.07 5.75 0.05 bmd1 0.00 bmdl
0800 1.55 2.68 0.09 4.15 0.14 0.44 0.05 bmdl 0.02 bmdl 0.08 0.06 bmdl 0.00 bmd1
C" 1200 1.92 2.80 0.09 5.38 0 .17 0.75 0.05 bmd1 0.04 bmdl 0.33 0.10 bmd1 0.03 bmdl
\J1 1600 2.29 2.90 0.10 6.64 0.23 0.93 0.15 bmd1 0.14 bmdl 0.57 0.18 bmdl 0.10 bmdl
2000 2.30 3.05 0.10 7.02 0.23 0.92 0.22 bmd1 0.20 bmd1 0.58 0.22 bmd1 0.13 bmd1
2400 2.31 3.15 0.12 7.28 0.28 0.91 0.20 bmdl 0.18 bmdl 0.58 0.35 bmdl 0.20 bmd1
4 1200 0.00 2.06 5.51 3.50 0.14 7.21 0.29 0.88 5.69 0.08 bmdl 0.07 bmdl 0.56 5.76 0.70 bmdl 0.39 bmdl
2400 1.81 3.90 0.24 7.06 0.43 0.84 0.16 bmdl 0.13 bmdl 0.54 1.08 bmdl 0.58 bmd1
1200 0.00 1.55 5.49 4.80 0.24 7.44 0.37 0.79 5.64 0.04 bmdl 0.03 bmdl 0.49 5.75 2.00 bmd1 0.98 bmd1
2400 1.28 5.30 0.24 6.78 0.31 0.74 0.04 bmdl 0.03 bmdl 0.43 2.40 bmd1 1.03 bmd1
1200 0.00 1.12 5.42 5.10 0.24 5.71 0.27 0.69 5.56 0.05 bmdl 0.03 bmdl 0.39 5.70 2.20 bmdl 0.86 bmd1
2400 0.95 4.95 0.24 4.70 0.23 0.64 0.05 bmd1 0.03 bmdl 0.34 2.25 bmd1 0.77 bmd1
1200 0.00 0.83 5.37 4.80 0.24 3.98 0.20 0.60 5.53 0.05 bmdl 0.03 bmd1 0.30 5.66 2.55 bmd1 0.77 bmdl
2400 0.71 4.70 0.22 3.34 0.16 0.56 0.20 bmdl 0.11 bmd1 0.26 2.65 bmd1 0.69 bmd1
8 1200 0.00 0.62 5.34 4.80 0.22 2.98 0.14 0.52 5.49 0.04 bmdl 0.02 bmdl 0.22 5.62 2.40 bmd1 0.53 bmdl
2400 0.52 4.90 0.21 2.55 0.11 0.48 bmd1 bmdl bmdl bmdl 0.18 2.15 bmdl 0.39 bmdl
9 1200 0.00 0.46 5.32 5.05 0.20 2.32 0.09 0.44 5.46 0.05 bmdl 0.02 bmd1 0.15 5.59 1.90 bmd1 0.29 bmd1
2400 0.40 5.15 0.18 2.06 0.07 0.40 0.05 bmdl 0.02 bmdl 0.12 1.67 bmdl 0.20 bmd1
10 1200 0.00 0.35 5.31 5.30 0.16 1.86 0.06 0.38 5.44 0.05 bmdl 0.02 bmd1 0.10 5.56 1.30 bmd1 0.13 bmdl
2400 0.29 4.90 0.14 1.42 0.04 0.35 0.04 bmdl 0.01 bmdl 0.08 1.10 bmd1 0.09 bmd1
11 1200 0.00 0.25 5.31 4.50 0.13 1.13 0.03 0.33 5.41 0.04 bmd1 0.01 bmdl 0.06 5.53 0.'35 bmdl 0.06 bmd1
2400 0.20 4.10 0.11 0.82 0.02 0.30 0.04 bmdl 0.01 bmdl 0.05 0.80 bmdl 0.04 bmdl
12 1200 0.00 0.16 5.31 3.70 0.09 0.59 0.01 0.28 5.39 bmd1 bmdl bmdl bmdl 0.04 5.51 0.65 bmd1 0.03 bmdl
2400 0.12 3.25 0.10 0.39 0.01 0.26 bmdl bmd1 bmd1 bmdl 0.03 0.60 bmd1 0.02 bmd1
13 1200 0.00 0.09 5.30 2.85 0.10 0.26 0.01 0.25 5.38 bmdl bmdl bmdl bmdl 0.03 5.49 0.55 bmdl 0.02 bmd1
2400 0.06 2.45 0.11 0.15 0.01 0.24 bmdl bmdl bmdl bmd1 0.02 0.50 bmd1 0.01 bmd1
14 1200 0.00 0.03 5.28 2.00 . 0.14 0.06 0.00 0.23 5.36 bmdl bmdl bmd1 bmdl 0.01 5.48 0.45 bmd1 0.00 bmd1
2400 0.01 1.60 0.16 0.02 0.00 0.23 bmd1 bmdl bmdl bmdl 0.01 0.40 bmdl 0.00 bmdl
. b~se1ine readings were taken before study on 3/15/75
10 m /ha/hr
c bmdl, concentration was below the minimum detection level. Minimum detection levels for N03-N and P04-P are 0.04 ppm and 0.06 ppm. respectively.
Discharge values for concentrations lower than these levels were not calculated.
-------
Table 21. Concentrations and fluxes of N03-N and P04-P in subsurface drainage water from ST,
DT, and DTL treatments during a 14-day per i od (February I 1-24, 1975) fol lowing a
5.7 cm irrigation. Plots were irrigated continuously over a 14-hour per i od. Rain-
fa I I occurred on days I I and 13. Water table height (W.T. ht.) are presented.
- - i.iiii Surface tilled - Tilled Deeo Tilled Li88d
now V.T. JOJ-II POt. - P IIOJ-II P04-P now V.T. IIOJ-II PQr, -p 103-11 PQr,-p now V.T. IIOJ-II P04-P IIOJ-II P04-P
E.u :ua !lll ..V Ht. Coac. Cone. Flux Flux ..t. Ht. COlIC. COGC. nux nux Rat. Ht. Cone:. Cone. Flux Flux
CII a - - JIII8 - - a/ha/hr - ab - - JIII8 - - a/ha/hr - ab - -PpIII- - a/ha/hr -
o' 0.00 5.19 ().8' 0.11 0.00 0.00 0.00 5.08 ~lc ~1 0.00 0.00 0.00 5.~0 0.07 _1 0.00 0.()0
1800 0.00 0.00 5.64 ~.60 0.1 -' 0.00 0.00 0.00 5.47 1811 1811 0.00 0.00 0.00 5.58 0.1~ bald 1 0.00 O.O()
2000 1.5J ..'.80 0.14 4.~8 0.21 0.05 1811 1811 1811 1811 0.00 0.12 bald 1 0.00 ().OO
1200 4.)1 J.I0 0.19 IJ.J6 0.8~ 0.18 1811 0.08 1811 0.01 0.00 0.12 bald 1 0.00 O.()O
2400 5.)2 J.5() 0.17 18.62 0.90 0.25 1811 0.10 1811 O.~ 0.00 0.12 bald 1 0.00 0.00
0200 0.00 5.00 5.10 J.51 O.B 18.00 0.58 0.28 5.60 0.04 0.18 0.01 0.05 0.55 5.n 0.85 0.08 0.47 0.05
OJOO 4.89 J.60 0.10 17.60 0.49 O.JO 0.04 0.16 0.01 0.05 0.11 0.95 0.08 0.71 0.06
0400 4.15 ) .66 0.10 11.10 0.47 O.H 0.05 0.12 0.02 0.04 0.76 1.00 0.08 0.78 0.06
0600 4.46 ).70 0.10 16.50 0.45 O.H 0.06 0.10 0.02 O.OJ 0.74 1.20 0.08 0.89 0.06
0800 J.85 J.87 0.10 14.10 0.J7 O.Jl 0.05 0.09 0.02 0.0) 0.73 1. JO 0.08 0.'15 0.06
1000 ).40 4.00 0.10 H.70 O. J6 O.JO 0.04 ().06 0.01 o.o:! 0.7) 1. J5 0.08 0.98 0.06
1200 J.11 4.05 0.10 15.0J 0.40 0.29 0.04 0.06 0.01 0.02 0.78 I.J8 0.08 1.07 0.06
1400 3.60 4.10 0.11 14.76 0.)9 0.28 1811 0.07 1811 0.02 0.81 1.60 0.09 1. JO 0.07
1600 3.5J 4.20 0.11 14.15 0.J9 0.28 1811 0.07 1811 0.02 0.80 1.80 0.09 1.44 0.07
1800 3.43 4.)0 0.11 14.15 0.J9 0.28 1811 0.06 1811 0.01 0.19 1.55 0.09 1.15 0.07
2000 J.22 4.40 0.11 14.19 0.J1 0.27 0.04 1811 0.01 1811 0.79 1.)0 0.09 1.0J 0.08
2400 3.02 4.50 0.12 H.59 0.J6 0.25 0.06 1811 0.02 1811 0.78 1.15 0.11 0.')0 0.09
J 1200 0.00 2.51 5.65 4.60 O.H 11.55 0.)) 0.2? 5.59 1811 0.06 1811 0.01 0.70 5.12 1.00 0.06 0.70 0.05
0'\ 2400 1.97 4.10 0.14 9.26 0.28 0.18 1811 1811 bm
-------
Table 22.
c:;..
-.....J
Concentrations, total discharges, and estimated percentage losses of N03-N and P04-P
in surface runoff water and subsurface drainage for 14-day periods following irriga-
tion amounts of 16.0, 8.2, 5.7 and 2.4 cm.
Irr.
Applied
- cm-
16.0
8.2
5.7
2.4
Soil
Treat.
ST
DT
DTL
STRO
DTRO
DTLRO
ST
DT
DTL
STRO
DTRO
DTLRO
ST
DT
DTL
STRO
DTRO
DTLRO
ST
DT
DTL
STRO
DTRO
DTLRO
NO)-N Conc
Mean Range
-ppm-
12.00
1.14
9.83
0.00
4.64
4.28
9.63
1.98
11.81
0.00
3.72
3.76
5.73
bald 1
1.00
bmd1
bmd1
bmd1
3.68
0.06
1.13
0.42
0.25
0.25
1. 78-18 .40
bmd1a-2.30
1.35-16.80
3.42-14.50
0.40- 2.66
0.60-30.00
0.82- 7.30
bmd1- 0.06
0.07- 1.80
0.30- 5.30
bmd1- 0.22
0.05- 2.65
POb. -P Conc
Mean Range
-ppm-
0.30
0.15
0.22
0.00
0.59
0.51
0.19
bmd1
bmd1
0.00
0.74
0.44
0.15
0.06
bmd1
bmd1
bmd1
bmdl
0.16
bmd1
bmd1
0.78
0.46
0.35
bmd1-0.43
bmd1-0.33
bmd1-0.28
0.11-0.31
bmd1-0.22
bmd1-0.16
0.11-0.19
bmd1-0.18
bmd1-0.11
0.09-0.24
bmd1-bmd1
bmd1-bmd1
Total
Flow
m3/ha
1127.74
938.06
485.16
0.00
91.70
148.70
511.83
268.39
237.42
0.00
11.00
80.00
797.70
51.61
157.42
1.85c
28.91
74.31
N03-N
Disc.
-kg -
14.40
0.57
5.13
0.00
0.43
0.64
5.38
0.45
3.48
0.00
0.04
0.30
4.44
traceb
0.14
0.00
0.00
0.00
252.90 0.95
154.84 0.01
49.03 0.09
0.07c trace
0.97 trace
1. 66 trace
P04-P
Disc.
-g-
387.84
72.00
106.80
0.00
54.10
75.84
138.06
6.71
5.42
0.00
8.14
35.20
123.22
0.77
3.74
0.00
0.00
0.00
41.03
trace
trace
0.05
0.45
0.58
N03-N
% Loss
33.98
1.34
12.10
0.00
1.01
1.51
12.69
1.06
8.21
0.00
0.09
0.71
10.48
neg
0.33
0.00
0.00
0.00
2.24
0.02
0.21
negd
neg
n"eg
P04-P
% Loss
8.39
1.56
2.31
0.00
1.17
1.64
3.00
0.14
0.12
0.00
0.18
0.76
2.67
0.02
0.08
0.00
0.00
0.00
0.89
neg
neg
neg
0.01
0.01
a bmd1, concentration was below the minimum detection level. Minimum detection levels for N03-N
and P04-P are 0.04 ppm and 0.06 ppm, respectively.
b trace, discharge values were less than 0.01 kg for N03-N and 0.01 g for P04-P.
c Surface runoff for this period resulted from rainfall which occurred after irrigation.
d neg, loss was less than 0.01 percent.
-------
Concentrations of NO~-N in subsurface drainage following irrigation
generally tended to increase with the quantity of water applied. For the
8.2 cm irrigation, maximum concentrations of N03-N were 14.50, 2.66, and
30 ~g/ml for ST, DT, and DTL plots. For unknown reasons, the concentration
of N03-N in drainage from DTL was especially large. For the 2.4 cm irriga-
tion, maximum concentrations of N03-N were 5.37, 0.20, and 2.65 ~g/ml for
ST, DT, and DTL plots.
Especially noteworthy is the observation that drainage following the
5.7 cm irrigation which was appl ied 3 months after a quarterly fertilization
initiated less discharge of nutrients from the soil profiles than when irri-
gation was applied within one or two days after application of fertil izer.
For 5T, DT, and DTL plots maximum concentrations of N03-N were 7.30, 0.06,
and 1.55 ~g/ml, respectively; whereas, maximum concentrations of P04-P were
0.19, 0.18, and O. 11 ~g/ml, respectively. Thus the length of the time per-
iod between times of fertilization and a rainfall or irrigation event defin-
itely is one of the factors resulting in enrichment of drainage water with
nutrients.
Figures 24, 25, and 26 show the results of the 5.7 cm irrigation applied
(beginning on February 11, 1975), 3 months after fertilization. The amount
of irrigation was sufficient to give a flushing action in ST only for both
N03-N and P04-P in that discharge peaks for both nutrients observed in ST
drainage water were at approximately 1.5 days after the initiation of the
irrigation. However, these peaks gradually subsided and the nutrient dis-
charge curves returned to base level by the 11th day (February 21) following
irrigation. On this data a rain occurred, followed by another on February
23, 1975, both of which totaled 7.17 cm. The additional rainfall initiated
additional concentration and discharge peaks for both N03-N and P04-P in the
5T plot, and a minor peak for N03-N in the DTL plot. The subsurface nutrient
discharge peaks for the 5T plot were very similar to those obtained following
the 8.2 cm irrigation of May 21, 1974. However, the concentrations and
nutrient discharges of the DT and DTL plots remained very low compared to
that for ST. This phenomena could possibly be explained by less nitrifica-
tion of N03-N in the deep-tilled plots.
Concentrations of P04-P in drainage tended to be relatively low compared
to that for N03-N. For the 5T plot, maximum concentrations of P04-P were 0.43,
0.31, and 0.24 ~g/ml in subsurface drainage following irrigations of 16.0, 8.2,
and 2.4 cm. For the DT plot, maximum concentrations of P04-P were 0.33, 0.22,
and 0.06 ~g/ml in subsurface drainage following irrigations of 16.0 8.2, and
2.4 cm. For the DTL plot, maximum concentrations of P04-P were 0.43, 0.16
and 0.06.~g/ml, respectively. For the 5T plot these peak concentrations
tended to 'occur several days earlier than those for DT or DTL plots.
The contribution of surface runoff water (Table 22) to the overall
nutrient enrichment of the perimeter ditch water was low from the DT plots,
less than 0.65 kg/ha N03-N for DTL (13% of the total loss) and less than
0.44 kg/ha for DT (77% of the total loss) after the 16.0 cm irrigation, and
was zero for 5T due to negligible water runoff from the 5T area during all
of the irrigation studies. During the 14-day period following the 8.2 cm
Irrigation (May 21 to June 3, 1974) the mean concentration of N03-N was
9.6, 2.0, and 11.8 ~g/ml for the 5T, DT and DTL plots. respectively, Dis-
68
-------
charges of N03-N were 5.4, 0.4, and 3.5 kg/ha, respectively.
Estimated percentage losses of N03-N in subsurface drainage were size-
able from the 16.0 and 8.2 cm irrigations (Table 22) for both 5T and DTL
treatments. During the 14-day periods, 5T lost nitrogen equivalent to 34.0%
and 12.7% of the nitrogen applied as fertil izer, respectively, while DT
losses were equivalent to 1.34 and 1.06% and DTL losses were equivalent to
12.1 and 8.2%, respectively, for the 16.0 and 8.2 cm irriqations. 5ince
ammonium and nitrate were the sources of N, only 45% of the appl ied
N was originally in the nitrate state. Thus the losses with respect to
percentages of applied N03-N were 68.0% and 25.2% for 5T, and 25.8% and 16.6%
for DTL following the 16.0 and 8.2 cm irrigations, respectively. Loss of
P04-P from 5T was 3.7 and 1.3% of applied phosphorus and 1.3 and 0.1% from
DTL after the two irrigations, respectively. Losses of N03-N and P04-P
generally were very small for the 5.7 and 2.4 cm irrigations.
Total drainage, N03-N discharge, and P04-P discharge during 14-day per-
iods following the 16.0, 8.2, and 2.4 cm irrigations are presented in Fig.
27 as functions of the water input to the soil from rainfall plus irriga-
tion. As shown previously in the report, drainage was always greatest from
5T, least from DTL, and intermediate from DT. For all three soil management
plots, drainage increased with total input of water from irrigation and
rainfall. Discharge of N03-N and P04-P with subsurface drainage also tended
to increase with total input of irrigation and rainfall. For any given
amount of irrigation plus rainfall, considerably more Nand P were discharged
with drainage from 5T than from either of the deep-tilled treatments.
Although discharge of P04-P was similar in drainage from each of the deep-
tilled plots, N03-N discharge from the DTL plot was greater than from DT
for the 8.2 and 16.0 cm irrigations. For the 2.4 cm irrigation N03-N dis-
charge was similar for DT and DTL. 5ince water flow was greater from DT
than DTL plots, the greater discharge of N03-N from DTL following large
irrigation events was associated with the larger N03-N concentrations
observed in drainage from DTL than from DT. The larger N03-N concentrations
could possibly be due to higher rates of nitrification for appl ied NH4-N
in the heavi ly 1 imed DTL soi 1. '
In Figs. 28, 29, and 30 water table
allel subsurface drains are plotted with
irrigations of 16.0, 8.2, and 5.7 cm for
plots.
depths at the midplane between par-
time during 10-day periods following
5T, DT, and DTL soil management
Water table depths from the soil surface were generally deeper in the
5T soil for a given rainfall event than in the DT and DTL soil profiles.
Drainage in the DT and DTL soils was usually slower due to smaller values
of hydraul ic conductivity and clogging of soil adjacent to the drains.
Higher water contents were thus commonly maintained in the surface DT and
DTL soil due to slower drainage than the 5T soil. Of the three irrigations,
only the 16.0 cm irrigation resulted in midplane water tables rising to the
soil surface. For the 16.0 cm irrigation the water table rise to the sur-
face was slower for 5T than DT and DTL, but the falling stage was obviously
much faster for the 5T plot. Water tables located at shallower depths in
DT and DTL treatments suggest the occurrence of higher soil water contents
69
-------
FIGURE 27.
15
,
,
,
,
/
,/
/,/'
,/
/
/
/
//
/
/
/
/
/
/
/
/
/
/
/
/
/
/
//
ST
DT
DTL
20
ST
20
ST
DTL
DT
20
Total drainage, N03-N discharged, and P04-P discharged versus
total rainfall and irrigation during three 14-day periods
(16.0, 8.2, and 2.4 em irrigations) for 5T, DT and DTL soil
management treatments.
E
.!,! 10
'"
0>
eu
c
iij
I-
a 5
5 10 15
Rainfall ard Irrigation (em)
15
~
g
~10
eu
.c
u
tI)
iJ
'7 5
M
o
Z
~----DTC
DT
00
10 15
Rainfall and Irrigation (em)
300
m
.c
0,
~
~200
I-
eu
.c
u
tI)
U
'7 100
~~
o
5 10 15
Rainfall and Irrigation (em)
70
-------
o
16 em Irrigation
20
......... 40
E
u
........
Q) 60
.Q
~
L 8
Q)
+-'
CU
~ 100
0
+-'
.c
+-' 120
Q.
<1>
0
1400 1
2
3
4 5
Time (days)
6
7
8
9
FIGURE 28.
Time-dependence of water table depth measured at a point mid-
way between two paral leI drain tubes for a 16.0-cm irrigation
(March 6-14, 1974)in ST, DT, and DTL plots. The water table
depth is taken as a distance beneath a point of zero depth
located midway between the elevations of the surface of the
soil bed and the bottom of the water furrow. The elevations
of the zero depth relative to mean sea level were 6.40 m for
the ST and DTL plots and 6.28 m for the DT plot.
71
-------
o
20
.........
~ 40
Q)
.0
('{1 60
I-
L
+-' 80
('{1
s
.8 100
.!:
+-'
Q.
120
0
1400 1
8.2 em Irrigation
2
3
4 5
Time (days)
6
7
8
9
FIGURE 29.
Time-dependence of water table depth measured at a point mid-
way between two parallel drain tubes for an 8.2-cm irrigation
(May 21-29,1974) in 5T, DT, and DTL plots.
72
-------
o
5.7cm Irrigation
20
.........
E
u
-- 4
1)
~
I- 60
L
+'
~ 80
~
o
+'
140
o
1
2
3
4 5
Time (days)
6
7
8
9
FIGURE 30.
Time-dependence of water table depth measured at a point mid-
way between two parallel drain tubes for a 5.7-cm irrigation
(February 11-19, 1975) in 5T, DT, and DTL plots.
73
-------
in the surface soil of these profiles. Generally, water tarl~s located
at the shallowest depths at the midplane between drainage in ST, DT, and
DTL treatments were associated with periods of maximum discharge of water
and nutrients from subsurface drains following a rainfall event.
SUMMARY
Results indicate that drainage of the three soil management systems
were greatly different. Drainage rates for subsurface drains in the ST
plots were much higher than for DT and DTL plots. Deep tillage on these
soils incorporated clay and organic materials from the subsoil layers into
the sandy surface soil, thereby decreasing the hydraul ic conductivity of the
soil in the root zone. In addition to changes in the soil particle-size
and pore size distributions, the drains in the DT and DTL plots appear to
be partially clogged (Rogers, Simmons and Hammond, 1971). Mechanical and
microbiological "clogging" of soil near drain tubes has been observed in DT
and DTL plots, and the resulting hydraulic resistence to water flow decreased
the drainage response of the deep-tilled plots. However, the decreased
drainage characteristics of DT and DTL plots provided improved soil water
storage capacities. There were also increased cation exchange. capacities
for the soil in the root zone which in turn resulted in larger growth rates
for young citrus trees than those planted in ST plots (Calvert et al., 1976).
Following rainfall or irrigation events, hydraul ic response of the ST
soil was particularly rapid and of greater magnitude than for DT and DTL
soils. Not only were peak flow rates for ST drains approximately 2 to 3
times greater than for other drains, but accumulative drainage of water from
ST drains was also more than twice that for DT and DTL. Deep tillage
appeared to decrease the magnitude of maximum subsurface drainage rates,
prolong "temporary" soil water storage over very long periods of time, and
resulted in slower drawdown of temporary water tables relative to that in
the 5T so i 1 .
Deep tillage appeared to decrease the quantity of N03-N that passed
through the soil and out through the drains. This decrease may be partially
due to the net influence of denitrification (see Section VI) during transport
of N03-N through the DT and DTL soils.
Although the magnitude of peak loss rates of P04-P from all drain lines
were considerably less than for N03-N, the loss of P04-P coincided in time
with those for N03-N. As expected, deep tillage drastically decreased
leaching losses of phosphorus fertilizer. However, incorporation of lime
in the deep tilled soil did not appear to greatly influence leaching of
phosphorus.
These and other data suggest that the subsurface drains in this Spod-
osol (5T treatment) provide rapid lateral water flow and tended to reduce
flow vertically through the chemically reactive, but slowly permeable spodic
horizon. The subsurface drainage of the layered 5T soil tended to increase
leaching losses of fertil izer nutrients.
Deep tillage tended, however, to decrease subsurface drainage, increase
74
-------
cation exchange capacity of the top 85 cm of soil, and decrease leaching
rates for N03-N and P04-P.
Hypothetical equivalent concentrations of the N03-N in the appl ied irrig-
ation water would be 13.1, 25.6and 87.5 Wg/ml for the 16.0-,8.2-, and
2.4-cm irrigations, respectively, if the nitrate were uniformly dissolved
and mixed in the appl ied volume of water. Considering rainfall occurred
early in the 2.4 cm irrigation period, the equivalent concentration would
be 39.3 wg/ml. Concentrations of N03-N in the drainage water from the DT
plot never approached values as large as the equivalent concentration. How-
ever, N03-N concentrations in the drainage from 5T and DTL plots after the
16-cm irrigation reached or exceeded the corresponding equivalent concentra-
tions. After the 8.2-cm irrigation of the DTL plot, N03-N concentrations
also reached or exceeded the corresponding equivalent concentration. The
highest corcentration of N03-N reached in the drainage water from the 5T
plot fol ing the 2.4 cm irrigation was 5.3 wg/ml (Table 20).
Before peak concentrations of appl ied fertil izer nutrients appear in
subsurface drainage water, infiltrated rain or irrigation water must flow
through the surface soil displacing the soil solution through the soil pro-
file. Powell and Kirkham (1974) showed that soluble components (example:
N03-N) of fertil izer appl ied to a bedded soil with subsurface drains will
move along streaml ines of water flow characteristic of the given bedding
geometry. For the case of drains placed beneath and parallel to each sur-
face furrow which separate parallel beds, they found that increasing the
bed slope would not only increase the volume of drainage through the soil
to the drain but would also cause the soil water and accompanying solutes
such as N03-N to move with greater velocity along comparable streamlines.
Potential theory (Kirkham, Toksoz and Van Der Ploeg, 1974) for subsurface
drainage of soil indicates that water infiltrating the soil surface directly
above a drain has the shortest streaml ine or pathway to that drain. Water
infiltrating the soil surface at greater distances away from the drain
encounters increasingly longer pathways to the drain. Water infiltrating
the soil surface near the midpoint between two parallel drains must follow
the longest pathway during drainage to the drain tube sink. Thus the water
flux from a subsurface drain will vary with time following an irrigation or
rainfall event, and for a given amount and intensity of water appl ied this
variation will be largely controlled by the curvil inear network of stream-
1 ines in a 2-dimensional plane normal to the axis of the drain. Also the
gradients of hydraul ic head and thus the water flow velocity along individual
streamlines will generally be greater for the shorter streamlines. In a
leaching study of salts from tile-drained sal ine soils, Talsma (1967)
observed that during the ponded stage of irrigation removal of salt from
the surface soil occurred more rapidly near the drains than midway between.
After ponding, i.e. during the fall ing water-table stages salt was removed
more evenly over the whole area. Thus, water infiltrating the soil surface
at some location near the midpoint between paral leI drains will generally
move more slowly and follow a longer pathway to the drain than water infil-
trating the soil immediately over the drain. Relatively nonreactive solutes,
such as chloride, will move approximately with the same velocity along a
given streaml ine as does the soil water; however, reactive solutes such as
P04-P, NH4-N and pesticides will move much slower than the water because of
75
-------
adsorption-desorption, chemical precipitation, microbiological tranformations
(nitrification) and synthesis, and other interactions with the soil matrix.
Nitrate-N is as mobile as the chloride ion but concentrations of N03-N which
occur in the soil solution and in the drainage water are influenced by micro-
biological transformations between ammonium, organic and nitrate forms and
denitrification which is a microbiological sink.
In response to a single irrigation or rainfall event,the drainage flux,
q(t), for a parallel system of subsurface drains generally tends to increase
exponentially with time to a maximum and then decrease exponentially after-
wards. For steady irrigation, q(t) occurs according to the Kraijenhoff Van
De leur-Maasland equation (Wessl ing, 1973; Van Schilfgaarde, 1974):
q(t) = O.81057Rl -!ir[l
n= 1 , 3 , 5
- e-(n'/j)t}
[1]
where R is the steady appl ication rate for water, t is time, and j = ~S2/~2T
is the reservior coefficient. The parameter ~ is the drainable pore space,
S is the distance between drains, and T is the transmissivity of the soil
(T=Kd where K is the saturated hydraul ic conductivity and d is the Hooghoudt
equivalent height of the drain level above an impervious soil layer). This
equation describes non-steady state drainage when initially (t=O) the
water table is horizontal and occurs at the drain level, when the hydraulic
head always remains as zero at the drain, and when irrigation or rain occurs
at a steady rate R over a time period t. This water flux as expressed by
q(t) represents the overall integrated influence of soil water movement along
many different streaml ines. As water infiltration results in water movement
downward and as the soil water pressure near the drain approaches or exceeds
zero to al low flow into the drain, the inital drainage water will flow
rapidly from the relatively short streaml ines in the soil above the drains
and with time drainage water will flow more slowly from the longer stream-
1 ines. Eventually the drainage will stop completely. Since soil water flow
represents a first approximation for movement of nonreactive solutes through
soils, the relative concentration C(t) of chloride or even nitrate in the
drainage water for fertil ized soil that receives irrigation or rainfall
should approximate the exponential behaviour of the water flux, q(t). How-
ever, adsorption-desorption and other interactions will result in a retard-
ation or lag with time for movement of reactive solutes such as P04-P, 2,4-D,
and terbacil relative to water flow. Thus, magnitudes of relative concen-
trations for solutes such as P04-P in drainage water should be low relative
to an inert ion 1 ike Cl. The Cl should also appear in the drainage water
prior to that for the P04-P.
Because of the large volume (3-dimensions) of soil drained by a given
length of subsurface drain, concentrations of solutes in the drainage water
would not be expected to undergo drastic changes over short time periods
(hours and days). Relatively long periods with nearly constant concentra-
tion of N03-N were in fact observed in drainage water from ST and DTl plots
following the 8.2- and 16.0-cm irrigations, and to some extent fol lowing the
2.4-cm irrigation for the ST plot. Also, a reasonably consistent quantity
76
-------
of water was observed to flow from the drains of the ST plot before the peak
N03-N concentration was reached. The exact quantities of water were 2.74,
3.57, and 2.41 cm, respectively, for the 16.0-, 3.2-, and 2.4-cm irriga-
tions.
The higher concentrations of nutrients observed in the drainage water
after fertil ization contrasts with the low concentrations, nearly zero,
observed in water from the Control plot during identical time periods. The
higher overall nutrient content from the grove area would confirm that the
agricultural practice of fertil ization does increase nitrogen and phosphorus
nutrient concentrations in the water. However, the lower concentrations in
the perimeter ditch and at the South Sump shows that these nutrients are
reduced significantly before being discharged into the drainage canals admin-
istered by the North St. Lucie River Water Management District and the Cen-
tral and Southern Florida Flood Control District.
Thus the DT and DTL soil management treatments with combined subsurface
drainage and deep tillage appeared to offer the advantages of (1) greater
capacity to retain infiltrated water against drainage loss, (2) greater cap-
acity to attenuate loss of appl ied fertil izer nutrients and pesticides with
drainage water, (3) providing a "buffering capacity'l against very fast rates
of water table rise during rainy periods, but increasing surface runoff over
surface tilled and (4) permitting the maintenance of an aerobic, unsaturated
root zone which has a large capacity to attenuate leaching losses of nitro-
gen and phosphorus and thus minimize pollution of nearby drainage canals.
A practical disadvantage of the deep tillage management is the high cost
relative to the shal low tillage management.
77
-------
SECTION V
CONCENTRATIONS AND FLUX OF CHLOROBENZILATE ACARICIDE AND TERBACIL
AND 2,4-DICHLOROPHENOXYACETIC ACID HERBICIDES IN SURFACE AND SUB-
SURFACE DRAINAGE WATER FROM A CITRUS GROVE
EXPERIMENTAL METHODS AND PROCEDURE
Three pesticides - chlorobenzilate (acaricide), 2,4-Dichlorophenoxy-
acetic acid (herbicide), and terbacil (herbicide) - were applied routinely
to the ST, DT, and DTL soil management plots of the SWAP citrus grove with
appl ication rates (Table 23) of 1.4,3.7, and 4.5 kg/ha, respectively, for
the three chemicals. Chemical structures for these materials are given in
Fig. 31. The chlorobenzilate was appl ied as an aqueous spray directly to
the citrus trees, whereas the terbacil was appl ied in aqueous spray to a
3-meter swath of soil along the rows of citrus. The 2,4-D was appl ied in
aqueous spray over a I-meter swath of soil along the midsection between
the two rows of trees along the top of each bed. Since the tree rows were
perpendicular to subsurface dra~n tubes, appl ications of these pesticides
were in bands which were also perpendicular to the drains.
Table23. Dates and quantities of 2,4-D,terbacil, and chlor-
obenzilate applied to 5T, DT and DTL experimental
plots.
Date
August 21-22, 1973
January 17-18, 1974
Ma r c h 4, 1 974
March 4, 1974
Ma r c h 4, 1 974
Ma y 20, 1 974
May 21-24, 1974
Ma y 2 1 - 2 4 , 1 974
July 10-11, 1974
March 11-13, 1975
March 11-13, 1975
Ma rch 11-13, 1975
Pesticide
terbac i 1
chlorobenzi late
terbac i 1
2 4-0
,
chlorobenzilate
chlorobenzilate
terbac i 1
2 4-0
,
chlorobenzilate
terbac i 1
2 4-D
,
chlorobenzilate
78
Application Rate
4 lbs. active/acre
1.25 pts./500 gal.
4 Ibs. active/acre
3 lbs./acre
1.25 pts./500 gal.
1.25 pts./500 gal.
4 lbs. active/acre
3 lbs. active/acre
1.25 pts./500 gal.
4 lbs. active/acre
2 1 b 5 . /100 ga 1 .
2.5 pts./500 gal.
-------
Following appl ications of these pesticides, samples of subsurface
drainage and surface runoff waters were taken at selected times, frozen,
and shipped to the Pesticide Research Laboratory in Gainesville for analyses.
Irrigation was sometimes used to initiate subsurface drainage, and all other
periods of drainage were attributed to rainfall. Sample size was approxi-
mately 100 ml of water.
Water samples were analyzed for concentrations of terbacil and chloro-
benzilate using the method of Pease (1966) and Wheeler et al. (1971) with
added modifications. THese changes included: (1) filtration of water sam-
ples to remove suspended materials, (2) adjustment of sample pH to 3-4 with
addition of HCl acid, (3) two extractions of the acidified sample using
100 ml volumes of ethyl acetate, and (4) concentration of the ethyl acetate
extract to provide an appropriate volume for analysis by gas chromatography.
An unpubl ished method by H. A. Moye was used to determine concentrations
of 2,4-0 herbicide as the butoxy ethyl ester in water samples. Each water
sample was first extracted for 2,4-0 using ethyl acetate, the same procedure
followed for chlorobenzilate and terbacil extraction. The next step was to
evaporate the ethyl acetate solution to dryness in a test tube using a gentle
stream of dry nitrogen gas. Preparation of the butoxy ethyl ester derivative
was as follows:(l) 5 ml of acetyl chloride was added dropwise to cold butoxy-
ethanol ( the final volume was 100 ml). (2) One tenth ml of this solution
was then added to the test tube containing the extracted 2,4-0. The tube was
sealed and held at SOoC for 30 minutes. (3) The tube was cooled and 2.0 ml
of hexane added to the tube. (4) The hexane solution was then extracted
three times with 0.2 ~ K2HP04 (the K2HP04 was discarded). (5) A small amount
of anhydrous sodium sulfate was then added to the solution to dry the sam-
ple. Gas chromatography was then used to determine the sample concentration
of 2,4-0.
>-~~
C-O-C2H5
Chlorobenzilate
)-CI
CI<
o
II
CH2-C-OH
I
o
H
I
N
H C-C/ ~C=O
3 1\ 1
CI-C~ /N- C(CH3)3
C
II
o
Terbacil
CI
2,4- Dichlorophenoxyacetic Acid
(2,4-D)
FIGURE 31.
Structural formulas for chlorobenzilate, 2,4-0, and terbacil
pesticides.
79
-------
, Average recoveries of terbacil, chlorobenzilate, and 2,4-0 from water
samples fortified with known concentrations were 80,83. and 85%, respec-
tively, when these analytical methods were followed.
Soil samples were removed, extracted, and analyzed for terbacil, chloro.
benzilate, and 2,4-0 content. An analytical procedure by Joll ifee et al.
(1967) was used to determine contents for terbacil and 2,4-0. Chloroben-
zilate analyses were performed using the method of Wheeler et al. (1969).
Operating parameters for the gas chromatographic analysis of extracts
from water and soil samples were as follows: Temperatures for the glass
column, injector and tritium electron-capture detector were 1850, 2250, and
2l00C. respectively; the column was 183 cm long with 4 mm inside diameter
and was packed with 3% QF-l on 80/100 mesh Gas Chrom Q (Appl ied Science).
The flow rate for the nitrogen carrier gas was 85 ml/min.
RESULTS ANO OISCUSSION
Concentrations (ppb or ~g/l) of terbacil and 2,4-0 in subsurface drain-
age waters from submerged and open outlet drains in ST, OT, and OTL soil
management plots are presented in Fig5. 32-35 for the first 67 days following
appl ications of terbacil, 2,4-0 and chlorobenzilate on March 5, 1974.
A 16.0 cm irrigation was applied (over a 39 hour period) on March 6 and
a total of 2.41 cm of rain occurred on March 14 and 15. Concentrations of
terbacil were always less than 130 ~g/l in drainage water, from all three
plots and concentrations of 2,4-0 did not exceed 80 ~g/ml. Chlorobenzilate
was not detected in the drainage waters at any time. Concentrations of
2,4-0 in drainage waters from ST and OT plots were always less than 25 ~g/l
and did not vary greatly between drain 1 ines with open outlets and submerged
outlets. Concentrations of 2,4-0 in drainage water from the submerged OTL
drain were lower (maximum of 75 ~g/l) in water from drains with open out-
lets. Earl ier, Calvert and Phung (1971) observed that concentrations of
N03-N in water from drains with submerged outlets from ST, OT, and OTL were
generally less than in drains with open outlets. They explained this dif-
ference in N03-N concentration by possible loss of N by denitrification in
the water-saturated soil above the drains with submerged outlets. Phung
(1971 and 1972) measured the dissolved oxygen content of drainage water from
ST, OT, and OTL plots, and observed lower oxygen concentrations in water
from submerged drains. Concentrations of 2,4-0 and terbacil were observed
to increase to broad maxima with time following the l6.0-cm irrigation.
For 2,4-0,the peak concentrations then decreased with time to near zero
values within 20 days after the irrigation. For ST and OT plots, the ter-
bacil concentrations decreased after the initial peaks and then increased
to form another peak later. Terbacil concentrations in drainage water from
the OTL drains decreased very slowly from the initial build-up of the peak.
The relative elution patterns for terbacil were essentially the same in
water from open and submerge~ drains.
Orainage water flux (flow rate), concentrations of terbacil and 2,4-0
and flux of terbacil and 2,4-0 in water from submerged and open outlet
,drains in ST, OT and OTL plots are presented in Figs. 36-47 for the first
80
-------
120
110
100
90
80
-I
~ 70
ID
a: 60
ILl
I-
ID 50
a-
a- 40
30 .
..
20
10
FIGURE 32.
120
110
100
...J 80
(3
~ 70
a:
ILl 60
I-
aJ 50
a-
a- 40
FIGURE 33.
TERBACIL (6MAR74-11 MAY 74)
SUBMERGED LINES
~ - ,6/
"""'''....... ",.;
- ....'"
I
..,............. '"
.' ..i ...... ....... .......... .....................
"'.'...
'.
"'."'''''''''''''-
- ST.S (2)
---- DT,S (17)
.......... D T L, S (II)
6
I
II
MAY
/1
26
I h
I
APR
I
29
7
8
9 10 II 12 13 14
MARCH
18
20
22
Terbacil concentrations in water from submerged drains in ST,
DT, and DTL plots during the period March 6 to May 11, 1974.
90
- ST,O (5)
----- DT,O (14)
........... DTL,O (8)
TERBACIL (6MAR74-IIMAY74)
OPEN LINES
30
;\
II ,:~~Y"""" i
.. I )/. ".:
'Ii .
.«
20
to
,. I
26
I
29
I
I
APR
Ir-r-
II
MAY
6
7
8
9 10 II
MARCH
12 13 14
18
20
22
Terbacil concentration in water from open drains in ST, DT,
and DTL plots during the period March 6 to May 11. 1974.
81
-------
CI 60
I
v. 50
(\J
CI) 40
a..
a.. 30
20
~ 50
v
N 40
II)
a.. 30
a..
90
80
70
2,4-0 (6MAR 74-11 MAY 74)
SUBMERGED LINES
10
- ..':.:..':':"'~"'UI4
o
6
7
18
20
22
8 9 10 II
MARCH
12 13 14
F I GU RE 34.
ST,O (2)
DT,O(l7)
DTL,O (II)
............
I
26
I
29
I
I
APR
~/ I
II
MAY
Concentrations of 2,4-0 in water from submerged drains in ST,
OT, and OTL plots during the period March 6 to May 11, 1974.
90
80
70
60
r..
! '\
: ~
i\...,..".!
2,4-0 (6MAR74-IIMAY74)
OPEN LINES
,.
r
: :
. .
! \
20
10
~/ I
26
6 7
8 9 10 II 12 13 14
MARCH
18
20
22
- ST,O (5)
---- DT,O (14)
-....,... 0 T L,O (8)
.......................
I
29
I //'
I
APR
I
II
MAY
FIGURE 35.
Concentrations of 2,4-0 in water from open drains in ST, OT,
and OTL plots during the period March 6 to May 11, 1974.
82
-------
~
...c:
"-
o
...c:
"-
I'0E
201
19
18
10
9
8
7
6
5
4
3
2
I
w
~
0:::
~
LL
2000
1800
'E I 600
"-
o
...c:
"- 1000
0'
.5 800
X
::::) 600
-.J
LL 400
200
Jl
Terbacil Submerged (line 2) I
ST
75
.0
50 Q.
Q.
25
7 8
Days
Water flux, terbacil concentration, and terbacil flux in water
from a submerged drain in the 5T plot during a l4-day period
(March 6-19, 1974) fol lowing a l6.0-cm irrigation.
FIGURE 36.
£ T~l
18
o
...c:
"- 10
1'0 9
E 8
7
£;
5
4
3
2
I
w
t:r
0::
~
-.J
l.L
2000
1800
E 1600
"-
o
...c:
'0,1000
E 800
X
:::) 600
-.J
l.L 400
200
FIGURE 37.
A
-- FLUX
-- ppb
2
3
10 II
12 13 14
4
5
6
9
Terbacil Open (line 5)
5T
A
-- FLUX
--- ppb
12 13 14
2 3 4 5 6 7 8 9 10 I 1
Days
Water flux, terbacil concentration,
from an open drain in 5T
period (March 6-19, 1974) following
100
75
.0
50 ~
25
and terbacil flux in water
plot during a l4-day
a l6.0-cm irrigation.
83
-------
~
.....
.c.
......
o
.c.
...... 10
!<) 9
..s 8
7
6
5
4
3
2
1
w
!:i
0:::
~
9
l.L.
~
.....
.c.
ci 300
.c.
......
C'
..s 200
X
:::>
...J
l.L. 100
50
FIGURE 38.
-
....
.J::.
.......
o
~ 10
!<) 9
E 8
7
6
5
4
3
2
w
!::(
a:::
3:
g
l.L.
-
....
~ 300
o
.c.
.......
0'>
.5 200
X
:J
.-J
l.L. 1 00
50
FIGURE 39.
Terbacil Submerged (line 17)
DT
-8- FLUX
-- ppb
100
75
.D
50:5:
25
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, terbaci1 concentration, and terbaci1 flux
from a submerged drain in the DT plot during a l4-day
(March 6-19, 1974) following a 16.0 irrigation.
in water
per i od
TerbacilOpen Oine 14)
OT
-- FLUX
-- ppb
100
75
.D
502t
25
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, terbaci1 concentration, and terbaci1 flux in
from an open drain in the DT plot during a 14-day period
6-19, 1974) following a l600-cm irrigation.
84
water
(March
-------
-
....
..c
.......
0
..c
....... 10
,.., 9
E 8
W 7
!;:t 6
5
0:: 4
~ 3
0 2
.--J I
I.J...
600 A
- 500
....
..c
'0 300
..c
.......
CJ>
S 200
X
=>
.--J
I.J... 100
....
..c
.......
2 10
,;)- 9
E 8
~ 7
W 6
~ 5
0:: 4
~ 3
g 2
I.J... I
400~
-.::
~ 300
o
..c
.......
CJ>
-5200
X
=>
.--J
I.J... 100
FIGURE 40.
FIGURE 41.
Terbacil Submerged (line I I)
DTL
50
-- FLUX
--- ppb
100
75
.D
50 ~
25
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, terbacil concentration, and terbacil flux
from a submerged drain in the DTL plot during a 14-day
(March 6-19, 1974) fol lowing a 16.0-cm irrigation.
in water
pe r i od
Terbacil Open (line 8)
DTL
-- FLUX
--- ppb
100
75
.D
50~
25
-------'---
. --'---...
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, terbacil concentration, and terbacil flux in water
from an open drain in the DTL plot during a 14-day period (March
6-19, 1974) following a 16.0-cm irrigation.
85
-------
FIGURE 420
FIGURE 43.
~
£.
'-
o
£.
'-
rc1
E
T~j
18J.-
10
9
8
7
6
5
4
3
2
I
w
tr
0::
~
~
-;::
£.
'-
E
'-
0'
S 200
X
::)
-.J
LL 100
50
Jl
2,4-D, Submerged (line 2)
ST
-- FLUX
-- ppb
100
75
.D
50 ~
25
2 3 4 5 6 7 8 9 10 I I 12 13 14
Days
Water flux, 2,4-0 concentration, and 2,4-0 flux in water from a
submerged drain in the ST plot during a l4-day period (March 6-
19, 1974) following a l6.0-cm irrigation.
~
£.
'-
o
£.
'-
rc1
E
~
2°i
19
18
10
9
8
7
6
5
4
3
2
I
w
tr
0::
~
9
LL
400
~
~ 300
E
'-
0'
S 200
X
::)
-.J
LL 100
50
2,4-D, Open (line 5) I
I
ST
-- FLUX
----- ppb
2
3
Water flux, 2,4-0
open drain in the
1974) following a
7 8
Days
concentration, and 2,4-0 flux in water from an
ST plot during a 14-day period (March 6-19,
16.0-cm irrigation.
86
4
5
12
13 14
6
9
10 II
150
100
75
.D
50 Q.
Q.
25
-------
FIGURE 44.
FIGURE 45.
-.::-
L
'-..
o
L
'-..
r<>
E
w
~
a::
3:
o
-.J
l.L
~
L
'-..
o
L
'-..
0'
E
x
::>
-.J
l.L 100
~
L
'-..
o
~ 10
r<> 9
S 8
7
6
5
4
3
2
I
w
~
a::
3:
o
-.J
l.L
~
L
'-..
o
L
'-..
0'
E
X
::>
-.J
l.L
7 8
Days
Water flux, 2,4-0 concentration, and 2,4-0 flux in water
from a submerged drain in the OT plot during a 14-day period
(March 6-19, 1974) following a 16.0-cm irrigation. .
10
9
8
7
6
5
4
3
2
I
2,4-0 Submerged (line 17)
DT
-- FLUX
-- ppb
50
2
3
4
5
6
9
13
14
10 II
12
2,4-0 Open {line 14)
OT
-- FLUX
-- ppb
100
75
.D
50~
25
100
75
.D
502t
25
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, 2,4-0 concentration, and 2,4-0 flux in water
from an open drain in the OT plot during a 14-day period
(t1arch 6-19, 1974) following a 16.0-cm irrigation.
87
-------
~
~
..c
"-
o
..c
"- 10
r<1 9
S 8
7
6
5
4
3
2
I
w
~
0:::
~
g
LL
~
..c
"-
o
..c
6,250
S200
X
::J I 50
-.J
LL 100
FIGURE 46.
~
..c
"-
o
..c
"-
f'")
E
w
~
0:::
~
g
LL
500
>: 400
..c
6 300
..c
"-
0'
S 200
X
::J
-.J
LL 100
'"
FIGURE 47.
2,4-0 Submerged (line II)
OTL
--- FLUX
--- ppb
50
100
75
.0
50 ~
25
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux, 2,4-0 concentration, and 2,4-0 flux in water
from a submerged drain in the OTL plot during a 14-day
period (March 6-19, 1974) following a 16.0-cm irrigation.
2,4-0 Open (I ine 8) I
OTL
10
9
8
7
6
5
4
3
2
I
11
-- FLUX
--- ppb
2 3 4 5 6 7 8 9 10 II 12 13 14
Days
Water flux. 2,4-0 concentration, and 2,4-D flux in
from an open drain in the OTL plot during a 14-day
(March 6-19, 1974) following a l6.0-cm irrigation.
88
75
.0
50 ~.
25
wate r
per i ad
-------
14 days after the 16.0-cm irrigation on March 6. For both terbaci1 and
2,4-0,peak zones of flux developed with time which coincided with the times
of peak water flux. Total discharges of 2,4-0 and terbaci1 were greatest
for ST drains, less from OTL, and least from OT. Concentrations of these
herbicides developed very broad peak zones which decreased within about a
week for 2,4-0 but did not decrease during the 14-day period for terbaci1.
Total discharges of 2,4-0 were greater in water from open outlet than from
submerged drains in ST and OTL plots. Oischarges of 2,4-0 from the OT plot
either through open or submerged drains was very small compared to that
from ST or DTL. Total discharges of terbaci1 were not greatly different
from open or submerged drains in ST, DT and OTL plots.
Concentrations of terbaci1 in drainage water from ST, DT and DTL soil
management plots are presented in Figs. 30 and 31 for a 14-day period
following an irrigation on August 22, 1973. As in the 1974 data, the con-
centrations reached broad maxima which were 2 to 10 days in duration. The
magnitudes of the concentrations did not appear to be significantly differ-
ent for open versus submerged drain outlets.
Terbaci1 concentrations and flux and water flux are presented in Figs.
48, 49, and 50 for drainage water from ST, DT and DTL plots during a 14-
day period in March 1975 that followed a 2.4-cm irrigation. Concentrations
approached peak values of about 22, 30 and 20 ~g/I in drainage from ST, OT
and OTL submerged drains, respectively.
.....
.J::
"-
C
.J::
"-
r<)
E
Terbacil Submerged (line 2)
ST
W
f-
30
-.J
LL 20
-- FLUX
-- ppb
10
100
75
.Q
30 :5:
25
FIGURE 48.
7 8
Days
Water flux, terbaci1 concentration, and terbaci1 flux in
water from a submerged drain in the ST plot during a 14-day
period (March 17-31, 1975) following a 2.4-cm irrigation.
2
3
4
5
6
9
10 II
12 13 14
89
-------
....
L
'-
o
L
'-
r<>
E
w
~
0:: 3
5: 2
o 1
Li 0
-.::
L
'-
o
L
'- 50
0>
S 40
X
::> 30
..J
LL 20
10
FIGURE '+9.
....
L
'-
o
L
'-
r<>
E
w
~
0::
5:
o
..J
LL
....
L
'-
o
L
'-
0>
E
x
:)
..J
LL 20
FIGURE 50.
Terbacil Submerged (line 17) I
OT
--------
------ FL UX
----- ppb
100
75
.D
50 a.
a.
25
2 3 4 5 6 7 8 9 10 I I 12 13 14
Days
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the DT plot during a 14-day
period (March 17-31, 1975) following a 2.4-cm irrigation.
Terbacil Submerged (line II) I
OTL
2
I
o
100
75
.D
50 ~
25
Water flux, terbacil concentration, and terbacil flux in
water from a submerged drain in the DTL plot during a 14-day
period (March 17-31, 1975) following a 204-cm irrigation.
---- FL UX
-- ppb
10
~~-----
-- -.....
.
2
3
4
5
6
7 8
Days
10 II
12
9
13
14
90
-------
In Fig. 51, the amounts of terbacil discharged within l4-day periods
following 16.0- and 2.4-cm irrigations (Table 24) are plotted versus the
sum of rainfall and irrigation. For the 2.4 cm irrigation terbacil discharge
was approximately the same for ST, DT and DTL plots; however, for the 16-
cm irrigation the amount of terbacil discharged was several fold larger for
the ST treatment than either DT or DTL. Data shown in Fig. 51 is for drains
with submerged outlets only. For the l6.0-cm irrigation in 1974, terbacil
discharge from open drains was only slightly greater than from submerged
drains; however, 2,4-D discharge from open drains was 2 to 3 times greater
than from submerged drains.
SUMMARY
Concentrations of terbacil and 2,4-D in the range of 0-130 ppb (~g/l)
were observed in subsurface drainage waters from ST, DT and DTL soil manage-
ment plots during the first few weeks following application of these herbi-
cides to the soil surface. These results were in agreement with earlier
laboratory work (Mansell et al., 1971) which showed that aqueous solutions
with 1000 ~g/l of terbacil could be miscibly displaced through water-satu-
rated columns of Wabasso sand. For the surface soil (0-10 cm profile depth)
peak terbacil concentrations were approximately 200 ~g/I and occurred about
0.5 pore volumes after the peak concentrations occurred for appl ied CI;
whereas for the subsurface (33-76 cm profile depth) soil, peak terbacil con-
centrations were 800 ~g/I and occurred at the same time as did the CI peak.
In that same work, acarol which is a chemical analogue of chlorobenzilate
moved very little during miscible displacement through the surface and sub-
surface Wabasso soi I. In this research, chlorobenzi late was not observed
in subsurface drainage water from ST, DT and DTL soils (Table 25). A single
application of terbacil in 1974, however, was observed to increase the con-
tents of terbaci 1 in the soi I by 856, 833, and 995 ~g/kg.
Discharge of terbacil and 2,4-D in subsurface drainage water followed
closely the flux of water from the drains. Relatively large water fluxes
were observed from the ST plot and thus the herbicide fluxes were greater
from ST drains than from DT and DTL drains. Thus deep-tillage appeared
to decrease losses of terbacil and 2,4-D in drainage water from this Spod-
oso I.
Concentrations of 2,4-D were generally higher in drains with open out-
lets relative to those for submerged drains. This difference in concentra-
tion may be attributable to greater microbiological degradation of the 2,4-D
molecule in the water-saturated soil near the submerged drains. Terbacil
concentrations did not differ greatly between water from open and submerged
drains. Some of the half-l ives reported (Table 27) for 2,4-D,terbacil, and
chlorobenzilate in soil are approximately 3-14, 150-225, and 21 days, respec-
tively. Hamaker (1972) reported characteristic times of 17 days for 2,4-D
and 184 days for terbacil as time required for 50% of appl ied chemical to
disappear from a soil.
9.1
-------
FIGURE 51.
~ ~
~
'"
'"
'"
'"
'"
15 /
'"
'"
'"
~
'"
'"
/
,..., '" ST
E '"
/
~ 10 /
'"
/ . DT
Q) '"
0> '"
ro /
/
C /
ro /
'"
L.. '"
0 /
5 / DTL
/
/
/
"
/
/
/
/
/
'"
'"
5 10 15 20
Rainfall and Irrigation (cm)
ST
75
~50
i
0>
L..
ro
L:
u
.~
025 DT
DTL
u
ro
.Q
L..
~
0 10 15 2
Rainfall and Irrigation (cm)
Quantities of subsurface drainage and terbaci1 discharged
with drainage water versus the amounts of rainfall plus
irrigation received for 14-day periods following irrigation
of 5T, DT, and DTL soil management p1otso
92
-------
Quantities of 2,4-D and terbacil pesticides discharged in
subsurface drainage waters from ST, DT, and DTL soil man-
agement plots during 14-day periods following an irriga-
tion of 16.0 cm (plus 2.41 cm of rain) during March 16-19,
1974 and 2.4 cm (plus 2.93 cm of rain) during March 17-31,
1975. Data is presented for subsurface drains with open
and submerged outlets.
2,4-D Discharged
ST DT DTL
------(g/ha)------
Tab 1 e24.
Date
Drain Outlet
1974
1974
Terbacil Dis6harged
ST DT DTL
------(g/ha)----~--
open 15.26 none 20.55 82.72 26.88 37.08
submerged 7.66 3.19 8.81 80.94 24.19 20.81
submerged 5.91 7.94 1. 49
1975
Concentrations (Wg/kg) of terbacil and chloro-
benzi1ate p~~ticides in 5T, DT and DTL surface
soil prior to and immediately following an app-
1 ication of these chemicals.
Terbac i 1
DT
(Wg/kg )
11 7
950
833
Table25.
Date
5T
DTL
February 29, 1974
Ma r c h 4, 1 974
Increase
558
1,414
856
146
1,141
955
93
Ch1orobenzilate
5T DT DTL
(Wg/kg )
000
000
000
-------
Table 26.
Total quantities of terbaci1 and 2,4-D discharged in subsurface
drainage water from ST, DT and DT~ plots during 14-day periods
following sequences of herbicide application and irrigation.
Discharges were measured from single drain tubes which each
drained areas of approximately 0.1673 hectares.
Pe r i od
Sampled
So i I Treatment
Ma rch 17- 31, 1975
ST
DT
DTL
March 6-19, 1974
ST
DT
DTL
ST
DT
DTL
* Outlet for drain tube was
** Outlet for drain tube was
Table 27.
Pesticide
Terbaci1 (submerged*)
Terbacil (submerged)
Terbacil (submerged)
Terbac i I
Terbacil
Terbac i I
Terbac i I
Terbac i 1
Terbac i I
(submerged)
(open** )
(submerged)
(open)
(submerged)
(open)
Quantity of pesti-
cide discharged
(g/ha)
35.3
47.5
8.9
483.9
494.5
144.6
159.5
124.4
221.7
45.8
91.2
19. I
o
52.7
122.9
Half-lives for chlorobenzilate, terbacil, and 2,4-0 pesti-
cides incubated in several soil substrates.
2,4-D
2,4-D
2,4-D
2,4-D
2,4-D
2,4-D
submerged
open.
(submerged)
(open)
(submerged)
(open)
(submerged)
(open)
Chemi ca'l
2,4-0
Substrate
so i 1 (JOoC)
Reference
Haque and Freed (1974)
2,4-0'
so i 1 that has
been treated
with 2,4-0 for
several years
Chlorobenzilate
soi I (Leon and
Lakeland sands)
Terbaci I
so i i (J 5°C)
Terbac i I
so i I (JOoC)
Half-life
3 days
10-14 days
21 days
225 days
150 days
Hassall (1969)
Wheeler et al
(1973)
. Haque and Freed
(1974)
Haque and Freed
(1974)
94
-------
SECTION VI
DENITRIFICATION IN SHALLOW- AND DEEP-TILLED SPODOSOL
EXPERIMENTAL METHODS AND PROCEDURES
The denitrification potential for the 3 tillage treatments - ST, DT
and DTL - was investigated to help explain the observed differences in ni-
trate loss in drainage water from these treatments. Denitrification as
used herein is the microbiological conversion of the N03-N ion to nitrogen
gases, primarily N20 and N2 and possibly NH3. This conversion occurs only
in the absence of 02 and in the presence of a readily available source of
energy (Stanford et al., 1975) for the facultative microorganisms mediating
these reactions. Such conditions are usually associated with water-satu-
rated soil, but sometimes may occur in micro-environments within a we11-
drained soil. Thus denitrification may occur in a macroscopically or seem-
ingly aerobic soil.
The redox potential (Eh) of a soil can be used as a qual itative indi-
cator of the type of reactions occurring within a soil since redox reactions
usually occur sequentially (Ponnamperuma, 1972). When the level of soil
oxygen is depleted to very low values, nitrate becomes an electron acceptor
in these reactions rather than oxygen.
At a pH of 7, denitrification begins at an Eh of approximately +200 mv.
The Nernst equation indicates that each decrease in pH of 1 unit should
increase the redox potential by 59 mv; therefore, at pH 5 denitrification
should begin at about +318 mv. In real ity the dependence of Eh upon pH
varies considerably and for the normal range of soil pH, i.e., pH 5 to 7,
denitrification occurs in the Eh range of +200 to +350 mv.
Ponnamperuma (1972) states that disappearance of N03-N in flooded soil
usually fo1 lows first-order kinetics, which means that tne rate of denitri-
fication depends upon the concentration of nitrate. Rates of denitrifica-
tion were also stated to be greater in nearly neutral soils than in acid
soils. Stanford et al. (1975) measured denitrification rates for 30 soils
which differed widely in pH, organic C contents, texture, etc. They reported
apparent first-order rate constants (denQting the fractional loss of N03-N
per hour) ranging from 0.001 to 0.040 hr . The rate constants increased
with increasing levels of extractable soil carbon.
A laboratory study to determine the effect of tillage treatment on
denitrification potential of soil from the experimental site was conducted.
Soil samples were taken from profiles of ST, DT and DTL treatments to a depth
of 90 cm. Selected characteristics of the soil samples are given in Table
28. Eighty-five grams of soil and 25 ml of a 50 ug/ml N03-N solution were
95
-------
placed in a ~5 ml jar. After flushing the air in the jar with inert He gas,
the jar was sealed and incubated anaerobically for periods ranging from 3
to 25 days. At selected times, redox potential and pH measurements were
made. Redox potentials were obtained using a platinum electrode. Electrodes
were slowly moved about in the sample during measurement and minimum read-
ings were recorded. The sample was then stirred under N2 gas and an average
Table 28: Physical and chemical characteristics
of ST, DT, and DTL so i 1 samples from
the SWAP citrus grove.
Soi 1 Sample Organic
Treatment Depth pH Matter
--cm-- ---%---
ST 0-30 4.6 1068
30-66 4.2 0.31
66-81 4.3 0.22
8l-90(Spodic) 4.5 2064
DT 0-30 4.5 2064
30-60 3.9 1021
60-90 4.2 1.39
DTL 0-30 5.7 1.67
30-60 5.6 1.69
30-90 508 1.60
Eh was taken. Each sample was then filtered and the filtrate analyzed for
N03-N. Nitrate disappearance was attributed to denitrification.
During the intensive sampl ing periods of March and May, 1974, Eh mea-
surements were made on the tile drainage water and in the soil profile.
Water samples were taken from the tile 1 ine in a 100 ml container and Eh
was read immediately using a portable pH meter with a mill ivolt readout and
a combination pt electrode. Soil Eh values were obtained by placing con-
structed pt electrodes (18 gauge Pt wire fused to 12 gauge copper wire) at
several depths in the soil profile during the sampl ing period.
RESULTS AND DISCUSSION
In the laboratory study, redox potentials of the surface (0-30 cm) sam-
ple from ST (Table 29) showed soil microenvironments capable of supporting
denitrification developing within 3 days and persisting throughout the
experiment. Redox potentials of the microenvironments are characterized
by the minimum Eh values. Nitrate in the surface horizon was essentially
depleted by the end of the experiment (Fig. 52). In contrast, little
96
-------
Table 29: Redox potentials observed during anaerobic incubation of the 5T soil
samples.
Time, Days
Depth 0 3 6 9 19 25
avgo min. avg. min. avg. min. avg. min. avg. min.
--cm-- ---------------------------------------mv--------------------------------
0-30 520 445 185 465 165 408 70 335 105 360 195
30-66 570 545 305 525 465 470 105 435 135 470 155
66-81 585 605 605 605 535 640 585 485 485 645 595
81-90 490 405 375 505 425 458 365 435 355 455 390
depletion of N03-N occurred in the lower horizons, 1 ikely due to a lack of
an energy source as suggested by the low organic matter contents of the 30-
66 and 66-80 cm samples. The lower N03-N concentrations noted in the 5podic
samples were due to dilution of the N03-N solution by the high initial mois-
ture content of this sample. Even though the spodic layer sample contained
more organic matter than the overlying material, this organic matter is
apparently not in a readily available form (Phung, 1972)-
Mixing of the soil profile, in DT and DTL plots resulted in a redistri-
bution of the organic matter throughout the top 90 cm of the soil profile.
Redox potentials of DT samples decreased to below +350 mv at all depths but
the lowest values were obtained in the surface sample (Table 30). For soil
sampled at equivalent depths, redox potentials of DTL samples (Table 31)
were lower than for DT samples. Nitrate disappearance (denitrification)
Tab 1 e 30:
Redox potentials observed during anaerobic incubation of the DT soil
samples.
Depth
o
3
6
Time, Days
9
19
avg.
mino
avg.
min.
avg.
min.
avg.
min.
25
avg.
mino
--cm--
---------------------------------------mv--------------------------------
555
605
405
495
495
455
245
235
465
105
445
125
0-30
30-60
165
385
315
435
465
205
510
225
522
115
60-90
605
445
225
485
305
455
335
500
2~
97
-------
occurred at all depths in the mixed profiles (DT and DTL) but at a much
slower rate than in the ST surface horizon (Figs. 52-54). Also, denitrifi-
cation occurred at a faster rate in the DTL samples than in the DT samples.
At this point it is not known whether this difference was due to greater
organic content or lower acidity in DTL due to 1 iming. Rates of denitrifi-
cation obtained for the surface horizon of ST and an average of the 3 depths
in DT and DTL were 2.24, 0.44, and 0.88l0-3/hr.
During the intensive sampl ing periods of March and May 1974, Eh measure-
ments were made on subsurface drainage water and soils from each tillage
treatment (Tables 32-35). Redox potential was measured in both open and sub-
merged drain I ines. With the exception of DT drains there was I ittle differ-
ence between open and submerged drains. The submerged drains in DT initially
had Eh values lower than the open I ines, but these difference tended to
disappear with time. These differences are I ikely due to the submerged
50
ST
i . . Q-30cm
0-----0 30-66
-- 0
.... . ......... 66-81
\\ ~~
\ O''''~'''''''''O 81-90(clf'V'"'\dic) "...
......-.. \ '+"-' ,-",'....
. \ @)----------------O.8
(~. ............................,
.
,1..,..".0#"1
"
"
"
"
"
"
"
"
'0
'"
.
'"
E 40
c..
Q.
Z 30
Of')
Z
20 '.'".,
';" []
'"
#'''' .,1' I'"
"" "..,.....".......
#'" """"0 " ,..,,,
0'"
10
o
4
8
12
DAYS
16
20
24
FIGURE 52.
Concentrations of N03-N in soil-water suspensions prepared
with soil samples removed from 0-30, 30-66, 66-81, and 81-
90 cm in the ST plot and anaerobically incubated for 24
days. The concentration of the applied N03-N solution was
50]Jg/ml.
98
-------
drains keeping the water table higher than the open drains.
not occur in 5T and DTL drains is not known.
Why t his did
Redox levels in the soil were measured at 30-cm intervals to 100-cm depth
directly over the drain and equidistant between two drains except for 5T
where measurements were made only over the drain. At 30 and 60 em the Eh
differences between the two locations varied inconsistently. However, at 100
em the Eh between the drains (except on March 6) was generally lower than
at the drain. Differences ranged from 10 to 425 mv and averaged 162 mv.
The soil Eh at 100-cm tended to be close to but slightly lower than the
drainage water Eh.
Redox potential of the drainage water and soil of the 5T treatment
remained above the level that would be expected to favor conditions for
denitrification during both periods. This is consistent with the laboratory
investigation which showed that the surface horizon was the only place where
denitrification would occur in the 5T treatment. Water was apparently
40
E
~30
10
FIGURE 53.
DT
.
. ,o~
.',' ~...~o --- 0
, . . ......
. ~......
8. ~~
. . . .1. ..... .
.......... .. -- ~
-. -....
... -...
... ........
..... 0 --- - 0--
'.
'.
'.
"." .,
'.
'.
'.
'.
.....
. . 0-30 em
0---- 0 30-60
. . . .. . . . .. 60 - 90
4
8
16
20
24
12
DAYS
Concentrations of N03-N in soil-water suspensions prepared
with soil samples removed from 0-30, 30-60, and 60-90 em
in DT plot and anaerobically incubated for 24 days. The
concentration of the applied N03-N solution was 50 ~g/ml.
99
-------
moving through the ST profile fast enough to prevent 02 depletion and thus
the Eh remained high. Only if the water table approached the soil surface
would denitrification be expected to occur in the ST surface horizon. Such
conditions occurred only during periods of intense rainfall or prolonged
irrigation.
In the DT treatment, redox levels at 30 and 60 cm were above the range
in which denitrification would be expected. However, at 100 cm depth, values
were in the denitrification range. This is especially true for the Eh meas-
ured in soil between drains. Drainage water Eh from DT was in the upper
part of the denitrification range.
The Eh of the DTL soil at 30-cm was also above the range where denitri-
fication would be expected. At 60-cm Eh was borderl ine to the denitrifica-
tion range and at 100-cm it was within this range. Drainage water Eh was
again on the borderl ine of the denitrification range.
40
E
8: 30
z
I
9.M 20
FIGURE 54.
.
DTL
. 0-30 em
0----0 30-60
\' ......... 60-90
( ....
\. .........
, ...
, .-.~......
\ ... .
0___- .... .-
0..... .
-.. --------'-r------ 0...... .8
-. -... .
.... ..--... 0....
. .
. 8..8
.. .
.. ....
10
.-
--.-
4
8
20
24
12
DAYS
16
Concentrations of tWrN in soil-water suspensions prepared
with soil samples removed from 0-30, 30-60, and 60-90 cm in
the DTL plot and anaerobically incubated for 24 days. The
concentration of the appl ied N03-N solution was 50 ~g/ml.
100
-------
Table 31. Redox potentials observed during anaerobic incubation of the DTL soi 1 samples.
Time, Days
Depth 0 3 6 9 19 25
avg. min. avg. min. avg. min. avg. min. avg. min.
-cm- -------------------------------mv-------------------------------------
0-30 515 375 175 420 180 407 -15 380 15 390 145
30-60 525 455 195 365 215 380 20 445 305 400 305
60-90 495 345 235 405 135 405 135 445 345
SUMMARY
Results from this study indicate that denitrification could provide a
significant sink for applied fertil izer nitrogen when rain or irrigation is
sufficient to move N03-N to within 100-em depth in the DT and DTL treatments.
However, if the added water is sufficient to cause continuous movement of the
N03-N through the soil and into the subsurface drain, the residence time
required for denitrification to occur in any significant amount wi 11 depend
upon the period of time required for the N03-N to move with soil water along
a given streaml ine or pathway from the soil surface to the subsurface drain.
N03-N from fertilizer appl ied to the soil directly over a drain should follow
the shortest streaml ines and thus may have residence times too short for
denitrification; whereas N03-N from fertil izer appl ied to the soil furface
at a distance midway (9.14 m) between two drains would be expected to follow
streaml ines with the maximum pathlength and with residence times much great-
er than that needed for denitrification to occur. Observed drainage responses
to irrigation and rainfall suggests that denitrification loss of N03-N in
fertil ized DT and DTL plots should be greater than in the ST plot during
subsurface drainage because of the greater rates of denitrification in the
subsoil and because of the slower flux of drainage water and thus the longer
residence times of N03-N within the soil profile. During periods (summer
months) of much rainfall and in the absence of subsurface drainage, however,
Table:'J2.
Redox potentials measured in subsurface drainage water during the March, 1974
sampl ing period.
Treatment
Ti 1e2
Time1, hrs
17 19 21 24 30 40 46 53 64 Avg.
--------------------------------mv--------------------------------
ST 0 490 395 420 420 455 485 505 460 460 455
S 505 445 445 475 490 445 555 520 505 485
DT (\ 340 270 290 320 380 350 400 385 400 350
S 235 215 235 275 330 340 375 380 375 305
DTL 0 725 280 265 305 295 300 290 310 315 345
S 370 290 285 295 280 300 275 300 310 300
1 5, 1976
0 hr = Start of irrigation, March
20 = Open drain; S = submerged drain
101
-------
denitrification losses could easily occur more rapidly in the surface ST
soil than in the surface DT and DTL soils since the residence times required
for denitrification (with imposed conditions of no net soil water flow) were
2.55 and 5.10 times greater in surface DTL and DT soil than in surface ST
so i 1 .
Tab 1 e 33. In situ redox potentials of ST, DT and DTL soi Is
during the March, 1974 sampling period.
Electrode Ma rch 5 March 6 March 7 March 8
depth A", B", A B A B A B
inches
ST
12 660 495 475 455
24 630 575 505 535
36 435 465 465 545
DT
12 790 475 605 465 540 555 625 515
24 750 470 555 540 455 535 540 465
36 365 305 295 325 295 230 415 185
DTL
12 545 590 345 455 445 505 345 400
24 750 550 355 485 335 505 330 310
36 695 410 225 335 325 190 335 105
",A = electrodes placed over the drain.
B = electrodes placed between two drains.
102
-------
Table 34. Redox potentials measured in subsurface drainage water
from ST, DT and DTL plots during the May, 1974 sampl ing period
Time', hrs
Treatment Ti Ie -8 6 16 21 26 39 45 63 66 avg.
---------------------mv------------------------
ST 02 415 430 435 500 458 455 480 453 520 460
s3 445 455 475 505 505 515 495 490 520 490
DT 0 395 390 380 390 375 425 435 410 425 400
S 340 340 305 340 375 410 385 350 380 358
DTL 0 330 325 305 365 410 355 395 340 370 355
S 290 320 250 350 425 410 395 310 395 350
10 hr = start of irrigation, May 21, 1976
2
Open drains
3Submerged drains
Table 35. In situ redox potentials of ST, DT and DTL so i 1 s
during the May, 1974 sampling period. 24
Electrode May 20 May 22 May 23 May
depth A", B;~ A B A B A B
inches
ST
12 555 400 430 460
24 365 335 335 335
36 580 495 505 520
DT
12 635 710 530 615 485 600 420 565
24 505 460 350 505 345 555 275 420
36 280 -20 :310 -25 370 -55 335 220
DTL
12 460 690 350 565 355 530 365 515
24 505 430 235 415 255 345 255 305
36 280 255 305 265 255 245 265 190
*A = electrodes placed over drain.
B = electrodes placed between two drains.
103
-------
SECTION VII
DISTRIBUTION OF N03-N CONCENTRATION
AND WATER PRESSURE IN A DEEP-TILLED SPODOSOL
EXPERIMENTAL METHODS AND PROCEDURES
The simultaneous transport of water and nutrients in subsurface-drained
Spodosols is particularly important to phenomena such as nutrient uptake by
plant roots, leaching loss of nutrients into nearby canals, and the overall
consideration of the use-efficiency of applied fertil izer. During June of
1975 spatial (2-dimensions) distributions of soil water pressure and concen-
tration of N03-N were measured in DTL soil surrounding a subsurface drain.
These distributions were determined for selected times following a sequence
of fertil izer and ir~igation water appl ications and wer~ used to analyze
water and NOrN movement in t he so i 1 .
Soil water tensiometers comprised of porous ceramic cups, each hydraul-
ically connected to a separate mercury manometer, and soil solution samplers
comprised of slightly larger porous ceramic cups connected to a plastic pipe
were installed in the soil at selected horizontal and vertical distances from
a subsurface drain. Tensiometer cups were placed at vertical depths of 15,
30, 60, and 100 cm in the soil directly over the drain and at 0.91, 4.57 and
9.14 m distances on both sides of the drain. The solution sampler cups were
placed at similar locations in the soil but were placed approximately 30 cm
from the tensiometer cups. All tensiometers and solution samplers were loca-
ted within a row of citrus trees which was perpendicular to the drain. Soil
water pressure was determined from readings of tensiometers, and soil solu-
tion samples were removed from the soil solution samplers. A small electri-
cal vacuum pump was used to establ ish a partial vacuum within the air-space
of the sampler. Six hours later the vacuum was released and a sample of the
extracted water within the sampler was removed. These samples were later
analyzed for N03-N concentration.
Soil water pressure and N03-N concentration data was used to determine
2-dimensional graphs of water pressure and N03-N contours in the soil effect-
ed by the subsurface drain. On the morning of June 10, 1975 a quarterly
appl ication of 530 kg/ha of an 8-2-8 fertil izer was made. This appl ication
contained 42.42 kg/ha of N (19.07 kg/ha of N03-N and 23.31 kg/ha of NH4-N).
Between the period of 3:30 PM on June 10 and 1:00 AM on June 11, 3.86 cm of
irrigation water was appl ied to the plot. On June 12, 0.41 cm of rain
occurred.
RESULTS AND DISCUSSION
Soil water pressure distributions are given in Figs. 55-62 for 3:00 PM
on June 10, 9:50 Pt1 on June 10,1:10 AM on June 11,2:15 PM on June 11, 4:00
104
-------
PM on June 12, 7:45 AM on June 13, June 16, and June 18. These distributions
show that a water table (h=O) occurred in the soil between 65 to 75 cm depth
even prior to initiation of the irrigation. Soil above those depths were
water unsaturated. Contours of equal soil water pressure can be converted
to contours of soil water content using the characteristic water data from
Hammond, Carl isle, and Rogers (1971). Prior to initiation of irrigation the
DTL soil was slowly undergoing drainage as indicated by the larger vertical
gradients for soil water directly above the drain. However, the water table
was relatively flat at horizontal distances greater than 1.5 m from the
d ra in.
Distance to Drai n(m)
0 -8 -6 -4 -2 0 2 4 6 8
IDTL
20
-40
~
E
~ 40 -20
..c:
+-"
Q.
Q) 0
0
80
100
Drain~0
13:00 PM. June 10 I
rlGURE 55.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 3:00 PM on June 10, 1975.
Lines of equal water pressure are shown.
105
-------
o
-8
-6
Distance to Drain(m)
-4 -2 0 2 4
20
-
E 40
u
'-"
£
+-'
~60
o
80
100
FIGURE 560
6
8
lOTL SOLU--h= Oem 01 water
~
106
+20
I 9:50PM, June101
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 9:50 PM on June 10, 1975.
Drain-..8
Six hours after initiation of the irrigation at 3:30 PM, the water
table (h=O) had risen to the top 15 cm of the soil profile and ten minutes
after terminating the irrigation at 1:00 AM on June 11 the entire soil pro-
file was water-saturated. During the first 13.25 hours of the post-infiltra-
tion period the soil underwent sufficient drainage to lower the water table
to a depth of 25 to 30 cm from the surface by 2:15 PM on June 11. By 4:00
PM on June 12, which was 39 hours after cessation of irrigation, the water
table was still located at a depth of 35-40 cm, indicating a very slow
drainage rate for this deep-tilled sandy soil. The relatively larger gradi-
ents of hydraul ic head in the soil near the drain compared to those away
from the drain suggests the presence of a local ized resistance to water flow
in the immediate vicinity of the drain (Roger, Simmons and Hammond, 1971).
Drainage is also relatively slow in this deep-tilled soil because of the
relatively small values of hydraul ic conductivity (Hammond, Carl isle, and
Rogers, 1971) at water-saturation.
-------
By 7:45 AM on June 13, or 2.25 days after cessation of irrigation, the
water table was located at 40-45 cm depth, and by 5.5 days (June 16) after
cessation of irrigation the water table was located at 55-65 cm depth. By
June 18 or 7.5 days after cessation of irrigation the water table had re-
turned to the pre-irrigation depth of 65-75 cm. Even after 7.5 days the soil
was still undergoing a slow rate of drainage and water contents in the soil
(Hammond, Carl isle and Rogers,1971) ranged from saturation (34.0% by volume)
to approximately 27% by volume at 15 cm depth. Thus this soil water pressure
data clearly illustrate the relatively slow drainage of the DTL soil and the
corresponding high soil water contents in this deep-tilled soil. The slow
decrease of the water content in the surface 60 cm of this sandy soil is
largely responsible for better growth of citrus trees on DT and DTL plots
relative to the ST plot which drains very rapidly to give a corresponding
rapid decrease of soil water content. The slow drainage of the DTL soil
should also result in slower velocities of soil water movement which in turn
should provide slower rates of N03-N leaching in the soil.
o
-8
-6
Distance to Drain(m)
-4 -2 0 2 4
6
8
20
I DTL Soil I
h= +20cm of water
-
E 40
u
..........
£.
+J
~60
o
...40
+60
80
m
~
11:10AMJ June 11 I
100
Drain ---,.,.8
FIGURE 57.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 1:10 AM on June 11, 19750
107
-------
o
-8
-6
Distance to Drain(m)
-4 -2 0 2 4
6
8
DTL Soi I
20
-
E 40 +20
u
'-"
.£
+-'
~60
0
80
100
Ora i n-,..0
12:15 PMJ June 111
FIGURE 58.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 2:15 PM on June 11, 1975.
Distributions of N03-N concentrations in the DTL soil are presented
in Figs. 63-67 for noon on June 10, midnight on June 10, 9:30 AM on June
11, 2:00 PM on June 11, and 10:00 PM on June 12. Prior to initiation of
irrigation (3:30 PM on June 10) N03-N concentrations were relatively high in
the top 60 cm soil located at horizontal distances greater than 2 m from the
drain. THese concentrations were as high as 22 ~g/ml as compared to concen-
trations generally less than or equal to 2 ~g/ml in soil beneath 60 cm depth
and in all of the soil directly above the drain. Initial concentrations of
nitrate in the soil probably originated either as NH4-N or N03-N from pre-
vious quarterly applications of fertil izer (the last appl icatlon was 3 months
prior to this time). Since the water table at this time was approximately
at the 65-70 cm depth, the observed distributions of N03-N may be attributed
to loss of nitrogen by denitrification in the water-saturated lower portion
of the soil profile and gain of N03-N by nitrification of NH4-N previously
108
-------
adsorbed to soil particles in the water-unsaturated (and aerobic) upper 60
cm of the soil profile. The low concentrations of N03-N in soil above the
drain coincides with the soil which usually has the largest gradients of
hydraul ic head and thus the largest velocities for soil water flow for per-
iods of drainage following rainfall or irrigation events. Thus the relative-
ly rapid soil water movement in the soil above the drain during previous
rainfall events probably resulted in greater leaching of appl ied nitrogen
and thus the lower observed concentrations of N03-N.
By midnight on June 10 or exactly 8.5 hours after initiation of irriga-
tion at 3:30 PM, the contour for 10 ~g/ml of N03-N in the soil solution had
moved downward from the pre-irrigation location of 40-50 cm on either side
of the drain to the 50-70 cm depth. Concentrations greater than 100 ~g/ml
were located at approximately 30 cm depth at 9.14 m to the left of the drain
and at 15 cm depth between 3-7 m to the right of the drain. N03-N concentra-
tions in the vicinity of the drain were considerably less than 10 ~g/ml, how-
ever. Although the N03-N distribution clearly indicates the influence of the
Distance to 0 rai n(m)
0 -8 -6 -4 -2 0 2 4 6 8
IDTL Soill h=-20cm of water
- -
20
0
~
E 40
u +20
'-"
.s::::.
+-'
~60
0 +40
80
+60
100
Drain~. 14:00 PMj JUne12\
FiGURE 59.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 4:00 PM on June 21, 1975.
109
-------
o
-8
-6
-4
Distance to Drain(m)
-2 0 2 4
IDTL Soill
h = -20cm of wate
6
8
-
,-....
E 40
u
.........
o
20
80
+20
..c
+-1
g. 60
o
+40
D r a i n -,.. (/f/J
/ :-60
r 7:45AM) JUne131
~
100
FIGURE 60.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain at 7:45 AM on June 13, 1975.
infiltrating water moving the appl ied N03-N downward into the soil, the
right-hand side distribution clearly was not a mirror image of the left-hand
side as were the soil water pressure distributions.
By 9:30 AM on June 11 or 8.5 hours after cessation of irrigation, the
N03-N concentration distribution indicates a gradual downward movement of
the N03-N. By 13 hours (2:00 PM on June 11) after cessation of irrigation,
the concentration distributions show that the 10 ~g/ml contours had progressed
to the 80-85 cm depth on both sides of the drain but was located at the 30-
35 cm ~epth in.soil directly a~ove the ~rain. Concentrations of N03-N in
the sOil solution near the drain-was still much less than 10 ~g/ml. Approx-
imately 3 days (10:00 PM on June 12) after cessation of irrigation, the dis-
tribution of N03-N was essentially the same as that on June 11 at 2:00 PM.
Thus these N03-N distributions suggest that concentrations of N03-N in sub-
surface drainage water from DTL were low ( < < 10 ~g/ml) compared to maximum
concentrations observed in the top 60 cm of surface soil greater than 2 m
distance from the drain.
110
-------
Water flux and concentrations of N03-N in water from the submerged drain
for the DTL plot are presented in Fig. 68 for the period June 10-24, 1975.
The water flux increased to a maximum value at 4:00 PM on June 11 and then
slowly decreased with time thereafter. Concentration of N03-N in the sub-
surface drainage was initially 0.37 ~g/ml on June 10 and increased to a max-
imum value of 7.02 ~g/ml on June 16 at 8:00 PM. A comparison between Fig.
68 and Figs. 63-67 indicates that changes in concentration of N03-N in sub-
surface drainage followed changes in concentration in the soil solution
immediately surrounding the drain tube.
SUMMARY
Spatial distributions of soil water pressure and N03-N concentration in
DTL soil were determined for a period of days fol lowing a sequence of fert-
il izer and irrigation-water applications. Relatively slow drainage occurred
after the 3.86 cm of irrigation and water flow from the drain tube had not
ceased even after 7.5 days following cessation of water appl ication. The
o
-8
-6
-4
Distance to Orain(m)
-2 0 2 4
IOTL Soil! h=-40cm
~
6
8
of water
20
-20
..........
E 40
u
'-'
.c
+-'
~60
o
o
+20
80
100
Ora i n'-+ .
FiGURE 61.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain on June 16. 1975.
111
-------
slow drainage provided three beneficial effects: (1) water contents in the
top 60 cm of soil remained relatively high even after 7.5 days, thus pro-
viding an optimum soil water environment for growth of citrus trees, (2)
slow drainage resulted in relatively slow changes in soil water content and
thus low flow velocities for leaching of N03-N, and (3) during the entire
7.5 day period a water table was located at some depth in the soil, providing
an aerated zone of soil for nitrffication of appl ied NH4-N above the water
table and a denitrification sink for N03-N in the lower portion of the soil
near the subsurface drain.
Although N03-N concentrations in soil solution samples extracted from
the upper portion of the soil drainage field were as high as 120 ~g/ml, con-
centrations of N03-N in the subsurface drainage water were always less than
8 ~g/ml.
o
-8
-6
-4
Distance to Drain(m)
-2 0 2 4
IDTL Soill
h = -40cm of wa
6
8
20
100
~
Drain-"..8
-20
..........
E 40
u
'-'"
..c
+-'
~60
o
o
"
80
+20
I June 18 I
FIGURE 62.
Spatial distribution of soil water pressure (h) in DTL soil
surrounding a subsurface drain on June 18, 1975.
112
-------
-
E 40
u
.........
..c
+-'
g- 60
o
100
o
-8
Distance to Drain(m)
-4 -2 0 2 4
61 DTL Soil I
6
6
8
-6
20
80
(\2
Drain~~
I Noon, June10 I
FIGURE 63.
Spatial distribution of N03-N concentration in the solution
of DTL soil surroundin~ a subsurface drain at noon on June
10, 1975. Lines of equal concentration are shown.
113
-------
'"'
E 40
u
'-"
.£:
+"
~60
o
80
100
20
o -8
-6
Drain-
--. ~ I Midnight June 10 I
FIGURE 64.
Spatial distribution of N03-N concentrations in the solution
of DTL soil surrounding a subsurface drain at midnight on
June 10, 1975.
114
-------
o -8
-6
Distance to
-4 -2 0
IDTL
Drain(m)
2 4
6
8
20
.........
E 40
u
'-"
.r.
+-' 10
~60
o
80
100
Drain ~~
19:30 AMJ June 111
FIGURE 65.
Spatial distribution of N03-N concentrations in the solution
of DTL soil surrounding a subsurface drain at 9:30 AM on
June 11, 1975.
11,
-------
'"'
E 40
u
'-'
.s:::
+oJ
~60
o
100
o -8
Distance to Drain(m)
-4 -2 0 2 4 6 8
I DTL Soil I Nitrate-NCjJg/ml)
~ 50
-6
20
80
Drain '-~
12:OOPMJ June11 I
FIGURE 660
Spatial distribution of N03-N concentration in the solution
of DTL soil surrounding a subsurface drain at 2:00 PM on
June 11, 1975.
116
-------
-
E 40
u
.........
.£
+-'
~60
o
100
o -8
Distance to Drain(m)
-4 -2 0 2 4 6 8
I DT L Soi I I Nitrate-N(jJQ/ml)
~ 50
-6
20
80
Drain~~
11000 PMJ Ju ne 12\
Spatial distribution of N03-N concentration in the solution
of DTL soil surrounding a subsurface drain at 10:00 PM on
June 12, 1975.
FIGURE 67.
117
-------
FIGURE 68.
30
.........
L
.c.
--
~ 25
--
(")
E
~ 20
a>
+-'
CU
~ 15
a>
CJ)
g! 10
CU
L
0
-- 5
0
>(
.;1 0
LL
0 2 4
L
a>
+-'
CU
~
a>
Q')
CU
c
CU
L
a
.s .........
14
12
10
8
DTL Soil
6 8 10
Time (days)
12
14
16
DTL Soil
C E
.Q 01 6
+-':J..
CU.........
L
+-'
C
a>
u
C
o
U
z
,
(")
o
z
4
2
4
6 8 10
Time (days)
16
12
14
Flux of subsurface drainage and N03-N concentration in the
drainage water from the DTL plot with time during the 14-
day period from June 10-24, 1975.
ll8
-------
SECT I ON V I I I
PHOSPHORUS ADSORPTION-DESORPTION AND TRANSPORT IN SOIL COLUMNS
LABORATORY EXPERIMENTS
Selim et al. (1975) and Mansell et al. (1976) examined the dynamics of
processes which remove phosphorus from the soil solution during miscible dis-
placement of a phosphate solution through undisturbed cores of Oldsmar sand
(Spodosol). These cores were removed from an unfertilized and untilled area
adjacent to the SWAP citrus grove near Fort Pierce. Experimental methods and
procedures are recorded elsewhere (Selim et al., 1975 and Mansell et al., 1976).
Adsorption isotherms plotted as phosphorus sorbed, S, (~g/g of soil) ver-
sus phosphorus concentration, C, (~g/ml) in solution were linear for the AZ
subsoil and highly nonl inear for the surface Al and subsurface BZh or Spodic
horizons. The isotherms extended over a C range from 0-100 ~g/ml for Al and
AZ horizon materials and from 0-800 ~g/ml for the BZh horizon.
Phosphorus breakthrough curves (relative concentration, C/Co, versus rela-
tive volume of effluent, VIVo) were examined for miscible displacement of aque-
ous solutions of P and Cl anions from undisturbed cores of AI' AZ' and B2h soil
materials. The relatively inert Cl anion was observed to move more rapidly
than the more chemically active P anion through all three soil materials.
Although sorption processes resulted in some retardation of the P breakthrough
curves for the AZ soil, the curve shape was very similar to that for the Cl.
Breakthrough curves for P in effluent from Al and BZh soils were assymetrical
and extensive tail ing was observed for the desorption phase of the miscible
d i sp 1 acement.
Mansell et al (1976) used a transport equation for transport
solutes through soil to simulate P breakthrough curves for the AZ
and Al (Fig~_7e) soil cores. Reversible instantaneous as well as
adsorption-desorption processes gave relatively good descriptions
port through these soils.
of reactive
(Fig. 69)
kinetic
of P trans-
A MATH ~ODEL FOR TRANSPORT AND TRANSFORMATION OF PHOSPHORUS IN SOIL
With increasing residence time in the soil, orthophosphate-P appl ied to
the soil undergoes a progressive decrease in water-solubility and availability
to plants growing in the soil. Since several simultaneous chemical and phys-
ical reactions are known to transform applied P to several less-soluble forms,
Mansell et al. (1976) developed a mechanistic, multistep kinetic model to
describe both the transformations and transport of applied P during water
flow through soil.
119
-------
Phosphorus transformations were governed by reaction kinetics and con-
vective-dispersion theory was used to describe P transport in soil. Six
kinetic reactions - adsorption, desorption, mobil ization, immobilization,
precipitation, and dissolution - were considered to control P transformations
between soluble, adsorbed, immobilized (chemisorbed), and precipitated
phases. A schematic diagram of the P transformations is presented in Fig. 71.
1.0
0.8
0.6
o
~0.4
U
0.2
00
FIGURE 69.
7 .,
: "1
,. ,
'. I
, I
:. I
I I
~ I
I I
: I
.. I
, I
~ ,
: I
I ,
J
2
6
4
8
V/~
\
,
I ,
~ \
I ,
: \
I I
~. \
I ,
~. \
I .
~ \
I I
I . \
I . ,
\ .~..
.
A2 soil
v = 34.82 cm/hr
:i=005(23C-S]
--- 05=0. 5=0.23C
ot I
---- 05= O' 5=0.023C
ot I
.
10
12
14
16
Experimental data and predicted breakthrough curves (Mansell
et al. 1977) for phosphorus concentrations in aqueous efflu-
ent eluted from a water-unsaturated core of subsurface (A2)
01dsmar sand.
120
-------
The model was used to simulate P movement in a 100 cm long soil column
to which a 100 ~g/ml solution of soluble P was appl ied for a period of 2
hours at a steady water flux of 2.857 cm/hr. Water was then appl ied for the
next 98 hours at the same steady flux. Distributions of P in solution and
sorbed phases for a selected standard combination of values for the kinetic
rate coefficients is shown in Fig. 72. The striking feature of the solution
phase P is the very rapid attenuation of concentration with time and depth.
After the first 2 days (approximately 50 hrs.), the maximum concentration of
P in solution was only I ~g/ml and no appreciable P in either solution or
sorbed phases occurred beneath the 36 cm depth. The time-dependency of the
kinetic reactions provided a very distinct time lag between solution and
sorbed phases of P. In Fig. 73 the total quantity of solution phase P in
the soil was observed to decrease very rapdily with time as the adsorbed,
precipitated and immobil ized phases increased. Thus the kinetic transforma-
tions for PappI ied to this soil tends to decrease the downward movement and
thus the leaching loss of P from the column. Laboratory and field experi-
ments will be needed in the future to val idate and verify the assumptions
used in this model.
1.0 I ,
'( I A, soil
"
0.8 r
.
p. - - v= 9.27 cm/hr
0.6 ..-
a --
U
~ ( 0.345 )
kd 17C -5
0.4
0.2
00
4
8
12
16
20
24
28
32
vivo
FIGURE 70.
Experimental data
et. a 1. 1977) for
ent eluted from a
01 dsmar sand.
and predicted breakthrough curves (Mansell
phosphorus concentrations in aqueous efflu-
water-unsaturated core of subsurface (Al)
121
-------
,Sin k '*"tl
ILEACH I NGI
L_____~
k, - k3 -
:-si~k-.2i k 1l k5
Lf!-A~T_S_J 6 Phase ~
~ A Water-Sol uble
B Adsorbed
D C Immobilized
D Precipitated
Transformations
of
P Applied to Soil
F I GU RE 71.
A schematic diagram of a mechanistic multistep mathematical
model U~ansell, Selim and Fiskell, 1977) for transformations
of P applied to soil.
122
-------
P in
o
1I1
40
-2 -1
k1=10 k3=10 kslO
-3 -2 -1
k=1 k=lO k=10nr
2 4 '"6
50
16
100
o
1I1
-2 -1
k1=10 k3'l0 ~10
-3 -2-1
k =, k =10 k=10 hr
2 4 '"6
50
Distributions of solution and sorbed phases of appl ied P
during miscible displacement through a 100 cm long column of
a theoretical soil using a mechanistic, multistep kinetic
model (Mansell, Sel im, and Fiskell, 1977).
FIGURE 72.
123
-------
0> 160
E
.........
Q)
-
~120
Q...
----
o
tf)
c 80 I
,
,
,
Q...
~ 40
o
I-
FIGURE 73.
k=10 k =102 k =101
1 3 5
k= 1 k =103 k =1 02hr1
2 ~ 6
,--...... B phase
I """'- ~
--
D --
---
~ --
--
--
....- - - - - - ---..- .... --
~~ ~----
" - - -
" ---.
,
,
,
,
,
,
,
,
. ,
,
,
,
,
,
OQ
20
40 60
Tim e (h rs)
80
100
Total quantities of soluble, adsorbed, immobil ized, and ;'re-
cipitated phase P in a 100 cm column of theoretical soil with
time during miscible displacement as predicted by the model
of Mansell, Selim, and Fiskell, (1977).
124
-------
REFERENCES
1.
Alberts, R.R., E.H. Stewart, and J.S. Rogers. 1971. Ground water
recession in modified profiles of Florida flatwood soils. Soil and
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2.
Ayers, R.S. and R.L. Branson, Editors. 1973. Nitrates in the Upper
Santa Ana River Basin in relation to groundwater pollution. Bulletin
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3.
Biggar, J.W. 1970. Pesticide movement in soil water. Pages 107-119
in Pesticides in The Soil: Ecology, Degradation, and Movement,
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4.
Biggar, J.W. and R.B. Corey. 1969. Agricultural drainage and eutro-
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Correctives, National Academy of Sciences, Washington, D.C.
5.
Bingham, F.F., S. Davis, and E. Shade. 1971. Water relations, salt
balance, and nitrate leaching losses of a 960-acre citrus watershed.
So i 1 Sc i. 112: 41 0-418.
6.
Bolton, E.F., J.W. Aylesworth, and F.R. Hore. 1970. Nutrient losses
through tile drains under three cropping systems and two fertility
levels on a Brookston clay soil. Can. J. Soil Sci. 50:275-279.
7.
Brasfield, J.F., V.W. Carl isle, and R.W. Johnson. 1973. Spodosols
soils with a spodic horizon. Pages 57-60 of Soils of the Southern
States and Puerto Rico, Bulletin No. 174, Agricultural Experiment
Stations of the Southern States and Puerto Rico and the Soil Conser-
vation Service of the United States Department of Agriculture.
8.
Calvert, D.V. 1975. Nitrate, phosphate and potassium movement into
drainage 1 ines under three soil management systems. J. Envir.
Qual. 4:183-186.
9.
Calvert, D.V. and H.T. Phung. 1971. Nitrate-nitrogen movement into
drainage 1 ines under different soil management systems. Soil and
Crop Sci. Soc. of Florida Proc. 31:229-232.
10.
Calvert, D.V., J.G.A. Fiskell, R.S. Mansell, J.S. Rogers, L.C. Hammond,
L.H. Allen, D.A. Graetz, E.H. Stewart, and W.M. Castle. 1976.
Water and Soil Management For Citrus Production On Poorly-Drained
Soils. Project Statement No. 01778, Florida Agricultural Experiment
Stations, University of Florida, Gainesvil1~.
125
-------
23.
(References Con1t.)
11.
Erickson, A.E. and B.G. Ell is. 1971. The nutrient content of drain-
age water from agricultural land. Research Bulletin No. 31, Agri-
cultural Experiment Station, Michigan State University, East Lan-
sing, Michigan.
12.
Fausey, N.R. 1975. Numerical Model Analysis and Field Study of Shal-
low Subsurface Drainage. Ph.D. Dissertation, Department of Agronomy,
Ohio State University, Columbus.
13.
Fiske1 I, J.G.A. 1971. The effects of deep mixing and liming on cation
selectivities of a Spodosol. Soil and Crop Sci. Soc. of Florida
Proc. 31:223-228.
14.
Fiskell, J.G.A. and D.V. Calvert. 1975. Effects of deep tillage,
I ime incorporation, and drainage on chemical properties of Spodosol
profiles. Soil Sci. 120:132-139.
15.
Fiske11, J.G.A. and R.S. Mansell. 1975. Dependence of P sorption in a
Spodoso1 upon P rate, contact time, and deep tillage. Soi 1 and Crop
Sci. Soc. of Florida Proc. 34:34-38.
16.
Fiskell, J.G.A., E.H. Stewart, and D.V. Calvert. 1970. Control of
mobil ity of soil organic matter after trenching. Soil and Crop Sci.
Soc. of Florida Proc. 30:122-130.
17.
Frink, C.R. 1971. Plant nutrients and water quality.
Science Review (2nd quarter), pages 11-25.
Agricultural
18.
Forbes, R.B., C.C. Hortenstine, and E.W. Bistline. 1974. Nitrogen,
phosphorus, potassium and soluble salts in solution in a Blanton
fine sand. Soil Crop Sci. Soc. Fla. Pro. 33:202-205.
19.
Graetz, D.A., L.C. Hammond and J.M. Davidson. 1974. Nitrate movement
in a Eustis fine sand planted to millet. Soil Crop Sci. Soc. Fla.
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20.
Hamaker, J.W. 1972. Decomposition: quantitative aspects. Pages 253-
340 of Organic Chemicals in the Soil Environment, Vol. 1, edited by
C.A.J. Goring and J.W. Hamaker, Marcel Dekker, Inc., New York, N.Y.
21.
Hammond, L.C., V.W. Carlisle, and J.S. Rogers. 1971. Physical and
mineralogical characteristics of soils in the SWAP experimental
site at Fort Pierce, Florida. Soil and Crop Sci. Soc. of Florida
Proc. 31 :210-214.
22.
Hague, R. and V.H. Freed. 1974. Behavior of pesticides in the environ-
ment: "Environmental chemodynamics". Residue Reviews 52:89-116
(see page 108).
Hassall, K. 1969. World Crop Protection 2.
Rubber Company, Cleveland, Ohio.
Chemical
Pesticides.
126
-------
(References Con't.)
24.
Johnson, W.R., F. Ittihadieh, R.M. Daum, and A.F. Pi llsbury. 1965.
Nitrogen and phosphorus in ti Ie drainage effluent. Soil Sci. Soc.
Amer. Proc. 29:287-289.
25.
Jolliffee, V.A., B.E. Day, L.S. Jordon, and J.D. Mann.
of determining bromacil in soils and plant tissue.
Chern. 15:174-177.
1967. Method
J. Agr. Food
26.
Jury, W.A. 1975. Solute travel-time estimates for tile-drained fields.
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27.
Kaddah, M.F. 1976. Deep ti llage enhances crop growth in a stratified
sandy soil. Paper No. 75-1556 presented at the 1975 Winter Meeting
of the American Society of Agricultural Engineers, Chicago, Illinois.
28.
Kirkham, Don, Sadik Toksoz, and R.R. Van Der Ploeg. 1974. Steady flow
to drains and wells. Pages 203-244 of Drainage For Agriculture,
Monograph No. 17, American Society of Agronomy, edited by Jan Van
Schilfgaarde, Madison Wisconsin.
29.
Knipl ing, E.B. and L.C. Hammond. 1971. The SWAP study of soil water
management for citrus on flatwood soils in Florida. Soil and Crop
Sci. Soc. of Florida Proc. 31:208-210.
30.
Mansell, R.S., W.B. Wheeler, Lita Elliott, and Mark Shaurette. 1971.
Movement of Acarol and Terbacil pesticides during displacement
through columns of Wabasso fine sand. Soil and Crop Sci. Soc.
of Florida Proc. 31:239-243.
31.
Mansell, R.S., H.M. Selim, and J.G.A. Fiskel1. 1977. Simulated trans-
formations and transport of phosphorus in soi 1. Soi 1 Sci. (in press).
32.
Mansell, R.S., H.M. Sel im, P. Kanchanasut, J.M. Davidson, and J.G.A.
Fiskell. 1977. Experimental and simulated transport of phosphorus
through sandy soils. Water Resources Research 13:189-194.
33.
1972. Agricultural chemicals in relation to environmental
chemical fertilizers, present and future. J. Envir. Qual. .
Nelson, L.B.
quality:
1: 1-6.
34.
Nelson, L.B. 1975. Fertilizers for all-out food production. Pages
15-28 in All-Out Food Production: Strategy and Resource Imp1ications.
Special Publication No. 23, American Society of Agronomy, Madison,
Wisconsin.
35.
Pease, H.L. 1966.
Chern. 14:94-96.
J. Agr. Food
Determination of bromacil residues.
36.
Phung, H.T. 1971. Dissolved oxygen in tile-drain outflow water-measure-
ment and affecting factors. Soil and crop Sci. Soc. of Florida Proc.
31:233-237.
127
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49.
(references con't.)
37.
Phung, H.T. 1972. Reduction processes in modified Spodosol systems
and their effect on some plant responses. Ph.D. Dissertation,
University of Florida, Gainesville, 209 p.
38.
Ponnamperuma, F.N. 1972.
in Agronomy 24:29-90.
The chemistry of submerged soils.
Advances
39.
Powell, N.L. and Don Kirkham. 1974. Flow patterns of rain water
through sloping soil surface layers and the movement of nutrients
by runoff. Completion Report No. ISWRRI-64, Iowa State Water
Resources Research Institute, Iowa State University, Ames, Iowa.
40.
Reitz, Herman J. 1961. Why citrus needs nutrition. Better Crops With
Plant Food Magazine, American Potash Institute, Washington, D.C.
41.
Rogers, J.S. and E.H. Stewart.
in modified soil profiles.
33:148-150.
1974. Hydraulic gradients near drains
Soil and Crop Sci. Soc. of Florida.
42.
Rogers, J.S., C.L. Simmons, and L.C. Hammond. 1971. Drainage charac-
teristics of Oldsmar sand simulated on a resistance network. Soil
and Crop Sci. Soc. of Florida Proc. 31 :218-220.
43.
Selim, H.M., P. Kanchanasut, R.S. Mansell, L.W. Zelazny, and J.M. David-
son. 1975. Phosphorus and chloride movement in a Spodosol. Soil
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44.
Sites, J.W., L.C. Hammond, R.A. Leighty, W.O. Johnson, and K.D. Butson.
1964. Information to Consider in the Use of Soils of Flatwoods and
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45.
Stanford, G., R.A. Vander Pol, and S. Dzienia. 1975. Denitrification
rates in relation to total and extractable soil carbon. Soil Sci.
Soc. Amer. Proc. 39:284-289.
46.
Stewart, E.H. and R.R. Alberts. 1971. Rate of subsurface drainage as
influenced by groundwater levels in modified profiles of Florida
flatwood soils. Soi 1 and Crop Sci. Soc. of Florida Proc. 31:214-215.
47.
Tal sma, T. 1 967 .
Res. 5:37-46.
Leaching of tile-drained sal ine soils.
Aus. J. Soil
48.
Van Schilfgaarde, Jan. 1974. Nonsteady flow to drains. Pages 245-270
of Drainage for Agriculture, Monograph No. 17. American Society of
Agronomy, edited by Jan Van Schilfgaarde, Madison Wisconsin.
Wesseling J. 1973. Subusrface flow into drains. Pages 1-58 of Drain-
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(Reference con't.)
50.
Wheeler, W.B., H.A. Moye, C.H. Van Middlelem, N.P. Thompson, and W.B.
Tappan. 1969. Residues of endrin and DDT in turnips grown in
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51.
Wheeler, W.B., D.F. Rothwell, and D.H. Hubbell. 1973. Persistence and
microbiological effects of Acarol and Chlorobenzilate in two Florida
so i 1 s . J. Env iron. Qua 1. 2: 115-118.
52.
Wheeler, W.B., N.P. Thompson, B.R. Ray, and Merrill Wilcox.
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Science 19:307.
Ana'
1971.
Weed
53.
Zelazny. L.W. and V.W. Carl isle. 1971. Mineralogy of Florida Aeric
Haplaquods. Soil and Crop Sci. Soc. Florida Proc. 31:161-165.
129
-------
Appendix:
TITLES AND ABSTRACTS FOR PUBLISHED PAPERS RESULTING FROM THIS
RESEARCH
(1)
Sel im, H.M., P. Kanchanasut, R.S. Mansell, L.W. Zelazny, and J.M. David-
son. 1975. Phsophorus and chloride movement in a Spodosol. Soil and
Crop Sci. Soc. of Florida Proc. 34:18-23.
Phosphate (p) and chloride (Cl) movement was determined in an 01ds-
mar fine sand using miscible displacement techniques for undistrubed cores
from Al, A2' and B2h horizons.
Cl mobility exceeded that of P in the Al
and B2h soils.
In the A2 soil, the shape of the breakthrough curves for P
and Cl were similar.
Phosphorus adsorption caused much higher retardation
in P movement in the highly sorptive Al and B2h soils than in the A2 soil.
Asymmetry and excessive tail ing of P breakthrough curves for the Al and B2h
soils suggest nonsingular as well as nonequil ibrium adsorption of phosphorus.
These soils showed nonl inear adsorption isotherms.
Decreasing the pore
water velocity in B2h resulted in less elution of appl ied P but the effect
of pore velocity had negl igible effects upon P breakthrough curves for A2'
For the Al soil, less P was eluted from water-unsaturated than saturated
soil.
Calculated results did not adequately describe P movement; however,
good agreement was obtained for Cl movement in all soils.
(2)
Fiskel 1, J.G.A. and R.S. Mansell. 1975. Dependence of P sorption in
a Spodosol upon P rate, contact time, and deep tillage. Soil and Crop
Sci. Soc. of Florida Proc. 34:34-38.
Hectare-size plots of 01dsmar fine sand
(Alfic arenic haplaquod)
were previously surface tilled (ST), deep til led unl imed to 105 cm (DT), or
deep tilled with dolomite incorporation (DTL) prior to tile drainage.
Sam-
ples were taken at 10 depths in 15-cm intervals.
The samples were sieved
130
-------
and subjected to phosphate appl ications from 1 to 480 ~g Pig soil in 0.01 M
CaC 12'
Langmuir adsorption isotherms were made on four depths from each
soil modification and also P sorption was studied at 200 ppm Pig soil level
for periods of 3 minutes, 10 minutes,2 .hours, 1 day, and 14 days.
In the 5T
soil, 7, 87. and 89% of 200 ppm P were retained after 24 hours by the A, Bh,
and B22 horizons, respectively; in DT and DTL soils at corresponding depths,
P sorption ranged from 64 to 91%.
Most of the P sorption was attributed to
s pod i c so i 1 .
With B22 soil, P sorption was 1 inearly proportional on a semi-
log scale to contact time; however, with Bh soil and both DT and DTL (0-105
cm) soil, P sorption was not 1 inear with increase in contact time.
Phos-
phate loss to drainage was probable in 5T soil because of low P retention in
the A horizon and very low permeability of the Bh and B22 horizons; in DT
and DTL, incorporation of the latter horizons provided good P sorption in the
depths.
(3 )
Mansell, R.5., H.M. 5el im, P. Kanchanasut, J.M. Davidson, and J.G.A.
Fiske 11. 1977. Exper imenta 1 and s imul ated transport of phosphorus
through sandy soils. Water Resources Research (in press).
Reversible equil ibrium adsorption-desorption relationships were inad-
equate for describing the transport of orthophosphate through water-saturated
and unsaturated cores from surface (Al) and subsurface (A2) horizons of Olds-
mar fine sand.
Using a kinetic model with nonl inear reversible adsorption-
desorption improved descriptions of phosphorus transport through these soils.
Phosphorus effluent concentrations were described best using an irreversible
sink for chemical immobil ization or precipitation with a nonlinear reversible,
kinetic adsorption-desorption equation.
131
-------
(I.. )
Mansell, R.S., H.M. Selim, and J.G.A. Fiskel!.
formations and transport of phosphorus in soil.
1977. Simulated trans-
Soil Sci. (in press).
A mechanistic, multistep model was developed using chemical kinetics
and mass transport theory to describe transformations and movement of ortho-
phosphate in soil.
Soil phosphorus was assumed to occur simultaneously in
any of four primary phases:
water-soluble, physically adsorbed, immobil ized
(or chemisorbed) , and precipitated.
The kinetics of reactions which control
the transformation of phosphorus between any two of the four phases were
considered to be reversible and of Nth order.
A range of values for the
reaction rate coefficients were used in the model to describe the transport
of appl ied phosphorus in the solution phase during steady water flow through
a soil initially devoid of phosphorus.
(5)
Kanchanasut, Pimpan. 1974. Iniiluence of soil water content and flow
velocity upon miscible displacement of phosphate and chloride in undis-
turbed cores of a Spodosol. M. Sci. Thesis, Soil Science Department,
University of Florida, Gainesville.
Excessive tailing of the desprption slope of the P breakthrough
curves indicated that desorption process was very slow at low concentration
of P for soil cores from Al and BZh horizons.
In water-unsaturated condi-
tions, the breakthrough curves showed that P was less mobile than for satur-
ated cond it ions.
The behavior of P movement in undisturbed soil cores was investigated
using miscible desplacement techniques.
Undistrubed cores of 5.4 cm diameter
and 10 cm length were collected from the AI' AZ' and BZh horizons of non-
cultivated Oldsmar fine sand.
Three flow rates were used in studies of water'
saturated flow through the Al and AZ horizons.
Unsaturated flow was main-
tained with 15 and 30 cm soil water pressure in cores of Al and AZ horizons
13Z
-------
located in a specially designed air pressure chamber.
Aqueous solutions of
100 ppm P as Ca(H2P04)2 were displaced through aqueous 0.01 ~ CaS04 saturated
cores obtained from the Al and A2 horizons and 1000 ppm P was passed through
cores obtained from the B2h horizon.
Chloride-36 was used as a tracer of
water movement in the soil.
Analyses of the breakthrough curves indicated that rates of P move-
ment in Oldsmar fine sand were in the order of A2 > Al > B2h horizon.
The
movement of P in the A2 horizon was similar to that for 36Cl- indicating that
P was not retained by the soil.
133
-------
"-- -. -----:: "",",,,,,,,...,.....'-'-~=------,~-
1, REPORT NO,
EPA-600/Z-77-177
4, TITLE AND SUBTITLE
Fertilizer and Pesticide Movement from Citrus Groves in
Florida Flatwood Soils
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
2, 3, RECIPIENT'S ACCESSION-NO.
7, AUTHOR(S)
. . 8, PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
University of Florida
Gainesville, Florida
32611
1HB617
11. CONTRACT/GRANT NO.
R800517
12, SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory - Athens, GA
Office of Research and Development
U.S. Environmental Protection Agency
Athens Geor ia 30605
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPAj600jOl
15. SUPPLEMENTARY NOTES
16. ABSTRACT oncentratlOns an lSC arge amoun s 0 3-, ,+-, er lCl e,
terbacil herbicide, and chlorobeniilate acaricide were determined in surface and sub-
surface drainage waters from a citrus grove located in an acid, sandy flatwood soil of
southern Florida. The influence of fertilizer and pesticide upon water quality
was examined for citrus growing in three soil management treatments: ST (shallow-
tilled plowed to 15 cm); DT (deep-tilled and soil mixed within the top 105 cm); and
DTL (deep-tilled to 105 cm and 56 Mtjha of dolomitic limestone mixed with the soil).
Average annual losses of N03-N in both surface and subsurface drainage from ST,
DT, and DTL plots were equivalent to 22.1, 3.1, and 5.4% of total N applied as
fertilizer. Average annual losses of PO,+-P in both surface and subsurface drainage
from ST, ST, and DTL plots were equivalent to 16.9, 3.6, and 3.5% of total P applied
as fertilizer. Deep tillage was thus observed to greatly decrease leaching loss of N
and P nutrients. Loss of nutrients in surface runoff was very small for all three
plots. Although the magnitudes were less, deep tillage also decreased leaching
losses of terbacil and 2,4-0 herbicide. Discharges of these herbicides in subsurface
drainage were usually in the order: ST>DTL>DT. Discharge of 2,4-0 was greater from
drains with open outlets than from drains with submerged outlets. Discharge of
terbacil did not differ for open or submerged drains. Chlorobenzilate pesticide was
not detected in drainage water from either of the three soil treatments.
17.
a,
DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
b.IDENTIFIERS/OPEN ENDED TERMS
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c. COSATI Field/Group
Agricultural Chemistry~ Citrus Trees,
Herbicides, Irrigation, Pesticides
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