United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/S2-86/027 May 1986
Project Summary
The Lubbock Land Treatment
System Research and
Demonstration Project
D. B. George, N. L Altman, D. E. Camann, B. J. Claborn,
P. J. Graham, M. N. Guntzel, H. J. Harding, R. B. Harrist,
A. H. Holguin, K. T. Kimball, N. A. Klein, D. B. Leftwich,
R. L. Mason, B. E. Moore, R. L. Northrup, C. Becker Popescu,
R. H. Ramsey, C. A. Sorber, and R. M. Sweazy
During the 1930s the City of Lubbock
entered into a contractual agreement with
Dr. Fred Standefer to pump all the sewage
effluent to his farm, later to be known as
the Gray farm. As Lubbock grew, the Gray
farm was able to expand to encompass
1,489 ha. Nonetheless, the Gray farm
could not adequately manage the hy-
draulic flow pumped from the City of
Lubbock. Consequently, the farm was
over-irrigated and ground-water accumula-
tion occurred beneath the farm with
associated water quality problems.
In 1981, the Lubbock Land Treatment
System was expanded to include the
Hancock farm located 25 km southeast of
Lubbock and directly north of the City of
Wilson, Texas. The expansion was de-
signed to reduce the hydraulic and nutrient
overloaded condition of the Gray farm. The
combined area of the Lubbock Land Treat-
ment system was 2,967 ha (7,330 acres).
The primary irrigation mode employed
by both farms was spray irrigation using
center pivot irrigation machines. The
Lubbock Land Treatment System Research
and Demonstration Project involved the 1)
physical expansion of the Lubbock Land
Treatment System; 2) characterization of
the chemical, biological and physical con-
ditions of the ground water, soils, and
crops prior to and during irrigation with
secondary treatment municipal waste-
water; 3) evaluation of health effects of
slow rate land application of secondary ef-
fluent; and 4) assessment of the effects
of hydraulic, nutrient and salt mass load-
ings on crops, soil and percolate.
During the period when a portion of the
treated wastewater was diverted to the
Hancock farm, a decrease in the ground-
water level beneath the Gray farm was
measured. In conjunction with the lower-
ing of the ground-water table was an in-
crease in water quality beneath most of
the farm (primarily the ground water
underlying the spray irrigated areas). The
cultivation of alfalfa in the spray irrigated
areas was probably the primary factor af-
fecting the quantity and quality of
percolate.
Chemical and nutrient constituents in
the treated wastewater applied to the
Hancock farm were removed by the soil-
crop matrix. An increase in ground water
beneath the Hancock farm resulted from
deep percolation of surface runoff col-
lected in moats surrounding the reservoirs
and excavations constructed to reduce
flooding of crop land. Deep percolation of
surface runoff leached existing nitrate and
salt deposits within the soil profile to the
ground water; thereby, causing increased
ground-water nitrate and total dissolved
solids concentrations.
An epidemiological study conducted on
the populace in and surrounding the
Hancock farm indicated that wastewater
spray irrigation produced no obvious
disease during the project period. How-
ever, the rate of viral infections was slight-
ly higher among participants who had a
high degree of aerosol exposure. The polio
virus 1 infections during spring 1982 were
probably related to this exposure.
Agricultural studies showed that cotton
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arid grain sorghum produced greater yields
with increasing annual hydraulic loading
rates up to 3m ha/ha/yr. The highest
alfalfa yields were obtained in test plots
irrigated with 365 and 434 cm ha/ha/yr.
The alfalfa test plots appeared to remove
all nutrients applied in the wastewater
stream. Salts were leached beyond 91 cm
of soil in all plots receiving 60 cm ha/ha/yr
or greater. The Lubbock Land Treatment
System Research and Demonstration Proj-
ect was conducted by Lubbock Christian
College Institute of Water Research
(LCCIWR), Southwest Research Institute
(SwRI), University of Illinois (Ul), Univer-
sity of Texas at San Antonio (UTSA),
University of Texas at Austin (UT), and
Texas Tech University (TTU). The full
report was submitted in fulfillment of
CS806204 and CR807501 by LCCIWR
under primary sponsorship of the U.S.
Environmental Protection Agency. This
report covers a summary of research ac-
tivities performed from May 1, 1980
through December 31, 1983. This work
was completed on June 30, 1985.
This Project Summary was developed
by EPA's Robert S. Ken Environmental
Research Laboratory. Ada, OK, to an-
nounce key findings of the research proj-
ect that is fatty documented in five
separate volumes (see Project Report
ordering information at back).
Introduction
Agriculture is the major user of
freshwater in the United States with ap-
proximately 99 percent of the agricultural
water demand used for irrigation. Increas-
ing water demands by agriculture, industry
and municipalities have created severe
water shortages in various regions of the
United States and worldwide. Application
of municipal wastewater to agricultural
lands has been demonstrated to be a cost-
effective treatment method. This practice
results in water conservation by reducing
withdrawal of freshwater from surface
water and ground-water sources.
The Lubbock Land Treatment System
Research and Demonstration Program,
funded by Congress in 1978 (H.R. 9375),
was designed to address the various
issues concerning the use of slow rate
land application of municipal wastewater.
The project involved the 1) physical expan-
sion of the Lubbock Land Treatment
System; 2) characterization of the chem-
ical, biological and physical conditions of
the groundwater, soils and crops prior to
and during irrigation with secondary
treated municipal wastewater; 3) evalua-
tion of the health effects associated with
the slow rate land application of secondary
effluent; and 4) assessment of the effects
of hydraulic, nutrient and salt mass load-
ings on crops, soil and percolate.
The Lubbock Land Treatment System
consists of two privately owned farms. In
past years, the Gray farm suffered from an
inadequate storage and distribution piping
network to properly manage effluent pro-
duced by Lubbock's Southeast Water
Reclamation Plant (SeWRP). Consequent-
ly, an increase in ground-water elevation
and degradation of ground-water quality
occurred beneath the farm. The system
was expanded in 1981 to include the
1,478 ha Hancock farm which is located
25 km southeast of Lubbock, Texas. The
expanded slow rate land application
system encompassed approximately
2,967 ha. From June 1980 to October
1983, both farms were monitored to
assess the impacts on ground water, soils
and crops of: 1) reducing the hydraulic,
chemical, and biological mass loading for
the Gray farm; and 2) spray irrigation of
effluent to the Hancock farm which was
primarily a dry land farm for 10 years prior
to 1982. Furthermore, an epidemiologic
study was conducted at the Hancock farm
to assess the association between human
exposure to the wastewater used for ir-
rigation and the development of new
infections.
Description of Land Application
System Expansion
Lubbock's SeWRP consists of two trick-
ling filter systems and an activated sludge
system (Figure 1). Unchlorinated effluent
from the two trickling filter plants was
pumped to the Gray and Hancock farms.
A total wastewater discharge of approx-
imately 5.5 x 104m3/d (15 mgd) was to
be divided equally between the Gray and
Hancock land application sites. Effluent
from SeWRP was conveyed to the Han-
cock land from a three-pump, pumping
station through 25 km of 0.69 m force
main.
The diurnal flow variation within the
wastewater treatment system due to the
management of water between the trick-
ling filter plants and the activated sludge
plant reduced flow through the trickling
filters from 2:00 a.m. to 10:00 a.m. each
day to 315 m3/hr (2 mgd). The pump
capacity and sump were not designed to
absorb the variations in flow from the
trickling filter plant. Consequently, the
dynamic nature of the effluent hydrograph
made it impossible to operate two pumps
for more than 16 hours each day.
At the northern boundary of the Han-
cock farm, the effluent was routed
through three 0.38 m plastic irrigation
pipelines to three separate reservoirs. The
reservoirs were constructed on natural
playa lakes. The reservoir capacity was
adequate to provide emergency storage
during rainfall events, and to prevent the
necessity of irrigating during periods of
cultivation, seeding, and harvesting of
crops. Approximately 3.5 months of stor-
age were provided by the three reservoirs.
Irrigation pump stations were provided at
each reservoir. Constant pressures were
maintained throughout the system by a
variable speed (lead) pump and a constant
speed (lag) pump located on Reservoir 1.
Both pumps were controlled by system
pressure and discharge flow rate.
The hydraulic distribution system was
designed to irrigate 1,153 ha with 1,082
ha irrigated by electric drive center pivot
irrigation machines. Each center pivot was
designed to irrigate up to 15 cm in 20 days
after allowing for 20 percent loss due to
evaporation. Without the use of the reser-
voirs, five to six center pivots could be
operated at the same time, utilizing the
flow pumped directly from Lubbock's
wastewater treatment plant. Each center
pivot had a centrifugal booster pump. The
booster pumps increased the line
pressures to an operating level of 3.1 x
106 pascals (45 psi).
Effluent Quality
During 1980 and 1981, Lubbock's
SeWRP was producing an effluent from
the trickling filter system which had a
composition equivalent to a typical
medium untreated domestic wastewater.
The City of Lubbock's wastewater dis-
charge permit for SeWRP required the
plant to produce an effluent with a 30-day-
average 5-day biochemical oxygen de-
mand (BOD) not greater than 45 mg/l. Dur-
ing the project monitoring period the ef-
fluent BOD5 quality from SeWRP ranged
from a monthly high of 260 mg/l to a
monthly low of 27 mg/l:
Average Monthly
Effluent BOD6
Produced by
Lubbock SeWRP
Month
January
February
March
April
May
June
July
August
1982
mg/l
143
260
198
139
108
128
130
76
1983
mg/l
71
120
105
65
30
39
49
27
-------
September
October
November
December
69
171
63
86
43
31
63
49
This poor quality effluent was mainly
attributable to the malfunctioning of the
anaerobic digestion process. Table 1 char-
acterizes SeWRP effluent produced in
1980 and 1981.
During the spring of 1982, SeWRP
placed on-line additional anaerobic
digesters and rehabilitated the primary
clarifiers and rotary distributors of the
trickling filter plants. A much higher quali-
ty waste stream was pumped to the Han-
cock and Gray farms in 1982 through
1983.
The sewage treated by SeWRP was pri-
marily derived from domestic sources with
less than 30 percent contributed from
industrial sources. Trace metals levels con-
tained in SeWRP effluent reflected this low
industrial wastewater flow and presented
no potential phytotoxicity problems. Table
2 summarizes the concentration ranges of
specific trace metals measured in treated
wastewaters. No significant differences (a
= 0.05) in trace metal and mineral levels
were determined between any irrigation
water source from February 1982 to Oc-
tober 1983.
The low hydraulic loading to the Gray
farm and Hancock farm (20 to 60 cm)
could contribute to the accumulation of
salts within the upper soil profile. Without
proper salt management, salts could pose
future phytotoxicity problems to farmers.
The adjusted sodium adsorption ratio
(SAR) of the effluent stream from the
trickling plant averaged 21.6. Irrigation
water with an adjusted SAR above 10 may
create severe water penetration problems
and development of alkali soils.
Proper management of salts contained
in the irrigation water was viewed as the
most important task which would govern
the long-term success of the land applica-
tion system.
Since agriculture is the major industry
in the Lubbock area, herbicides (e.g.,
strazine and propazine) and byproducts
produced from the decomposition of her-
bicides (e.g., 2,3-dichloroaniline and
3,4-dichloroaniline) existed in the
SeWRP's effluent. Carbon tetrachloride,
chlorobenzene, and diethylphthalate levels
exceeded the respective organic concen-
tration range in municipal wastewater
treatment plants. A mean anthracene con-
centration of 6.1 ng/\, 4.0 ^g/l and 8.4
ng/l was contained in the effluent from
the trickling filter plant; wastewater
pumped to the Gray farm; and effluent at
the terminus of the force main,
respectively.
Aeration
Lime n Treatment
Supernatant
Gray
Farm
Trickling Secondary
Filters Clarifiers
Hancock Hancock
Lagoons Farm
Power
Utility
{ _ _» SuJdgeJnickener^ _ Digesters-^
"'Landfill
Supernatant
Digested Sludge
Figure 1. Southeast Water Reclamation Plant flow diagram.
-------
The average fecal coliform concentra-
tion in the waste stream pumped to the
center pivot irrigation machine exceeded
EPA guidelines throughout the study
period. The 1981 guidelines state:
"Biological treatment by ponds or
inplant processes plus control of
fecal coliform count to less than
1,000 MPN/100 ml — acceptable for
controlled agricultural irrigation ex-
cept for human food crops to be
eaten raw."
The actual flow-weighted average fecal
coliform concentrations of the applied
wastewater during the four major irriga-
tion periods were:
Fecal Coliform
Concentration
Colony Forming Units
|cfu)/100 ml
Table 1. Characterization of Effluent Produced by Southeast Water Reclamation Plant
in 1980 and 1981
Concentration
Spring 1982
Summer 1982
Spring 1983
Summer 1983
4,300,000
840,000
5,200
120,000
The most prevalent Enterobacteriaceae
species encountered in wastewater from
Lubbock included Citrobacter, Entero-
bacter, Escherichia and Klebsiella.
Aeromonas hydrophila was the most abun-
dant non-Enterobacteriaceae member
recovered, followed by Pseudomonas
species. The effectiveness of ponding for
the reduction of microbial numbers was
evident both by the lower levels and the
reduced diversity of organisms seen in a
single bacterial screen completed on a
sample from the Hancock reservoir. Since
microorganism densities were much
higher in the wastewater from the pipeline
than from the reservoirs, the exposure
which most of the study population
received to most microorganisms via the
wastewater aerosol was greater in 1982
than in 1983.
During system operation, the fecal col-
iform concentration of the waste stream
from SeWRP and the discharge from the
storage reservoirs greatly exceeded EPA
guidelines, especially in 1982. The effluent
BOD5 concentration produced by SeWRP
did not satisfy Texas permit requirements
until May 1983. The system, however, was
operated below hydraulic design capacity
in 1982 and 1983.
System Operation
Hancock Farm
The Hancock slow rate system had the
following alternative operational modes:
Parameter
Alkalinity (mg CaC03/l)
Specific Conductance (iunhos/cm)
Total Dissolved Solids Img/l)
PH
Chloride Ion Img/l)
Sulfate Ion (mg/l)
Total Kjeldahl Nitrogen (mg N/l)
Nitrite plus Nitrate Nitrogen (mg N/l)
Ammonia Nitrogen (mg N/l)
Total Phosphorus (mg P/l)
Orthophosphate Phosphorus (mg P/l)
Organic Phosphorus (mg P/l)
Chemical Oxygen Demand (mg/l)
Total Organic Carbon (mg/l)
Average
337
2216
1695
7.54
468
315
38.59
0.29
25.95
14.43
8.36
5.15
302
118
Standard
Deviation
34
290
537
0.21
55
43
15.23
0.30
6.69
4.27
2.03
4.20
136
45
Table 2. Concentration of Trace Elements in Treated Wastewater
Wastewater Effluent Median Concentration (mg/l)
Element
As
B
Cd
Cr
Cu
Hg
Mo
Ni
Pb
Se
Zn
Range*
(mg/l)
< 0.005-0.023
0.3-2.5
< 0.005-0. 2 2
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not crop requirements. Cotton was
the primary crop grown at the Hancock
farm prior to 1982. Rainfall and associated
hail during the months of May and June
1982 which were the 24th and 25th
months of the study monitoring period
destroyed over 8.09 x 105 ha (2 x 106
acres) of the cotton crop in the South
Plains of Texas. Only 16.2 ha (40 ac) of
cotton remained on the Hancock farm.
The majority of the farmers planted grains
to partially recuperate financial losses.
Tenant farmers at the Hancock farm
planted approximately 552 ha (1365 ac)
of grain sorghum, 162 ha (400 ac) of
sunflowers, and 257 ha (635 ac) of
soybeans.
During the summer of 1983, less than
2.5 cm (1 inch) of rain was recorded from
the end of June through mid-October.
Gray Farm
Secondary treated effluent from SeWRP
was delivered to the Gray farm through
three pipelines to three storage reservoirs.
The estimated hydraulic retention time of
the ponds was 10 days.
Prior to 1982, with 75 to 80 percent of
the farm planted in cotton, water was ap-
plied to the cotton areas in early spring,
February through April (prewater); and in
the summer from June through August.
An estimated 70 cm of water was applied
to the land designated for cotton planting.
Any other irrigation (the remaining six
months), with no storage, had to be put
on winter crop or grazing area. From two
to 4.5 m/yr was applied to these areas in
order to keep the main economic crop
(cotton) at maximum production. In the
spring of 1982 over 506 ha (1,250 ac) of
alfalfa, 304 ha (750 ac) of wheat, and 121
ha (300 ac) of soybeans were planted on
the Gray farm.
Conclusions
The findings of the project indicated
that the major recharge of ground water
beneath the Gray farm was from flood ir-
rigated wheat areas. Deep percolation of
irrigation water and precipitation con-
tinued in 1982 and 1983 in the flood ir-
rigated areas. Physical limits of irrigation
equipment, hydraulic distribution system,
water storage, and crop cultivation
eliminated the capabilities for proper water
management. With adequate winter
storage and the hydraulic capability to
distribute more water on the alfalfa in
1982 and 1983, minimal deep percolation
would have occurred through the soil
throughout the farm. Comparison of 1981
and 1983 ground-water elevation data in-
dicated that the ground-water levels
beneath the Gray farm decreased.
During the period from February 1982
to October 1983, an increase in the
ground-water quality also occurred
beneath most of the Gray farm. Mass
balances conducted on nutrient and
minerals indicated continued leaching of
constituents through a soil depth of 183
cm beneath the flood irrigated area,
whereas most of the chemical consti-
tuents applied by sprinkler irrigation were
retained and/or removed through crop up-
take beneath the spray irrigated areas.
Statistically significant decreases in
NO3-N levels were measured in five of 27
monitoring wells from February 1982 to
October 1983. In general, 17 of 27 wells
experienced a decrease in ground-water
NQ3-N levels. A comparison of baseline
data (June 1980 to February 1982) and
data collected after February 1982 in-
dicated a decrease in the frequency of
ground-water N03-N concentrations
equaling or exceeding drinking water stan-
dards in nine of 27 wells monitored.
Wastewater treated by SeWRP was
primarily derived from domestic sources
with less than 30 percent contributed by
industrial sources. Consequently, trace
metals posed no potential toxicity pro-
blems to humans or plants.
Total irrigation at the Hancock farm
varied from 16 cm to 20 cm in 1982 and
36 to 49 cm in 1983. An overall increase
in ground-water elevation occurred
beneath the Hancock farm. A maximum
rise of three to five meters was experi-
enced in ground-water wells in close prox-
imity to surface runoff collection areas.
Increases in ground-water elevation
beneath the Hancock farm were primarily
due to percolation of surface runoff
through coarse material contained in
moats surrounding the reservoirs and ex-
cavations constructed to reduce flooding
of cropland and migration of percolate
through material surrounding poorly
sealed well casings. Increases in ground-
water elevation commenced approximate-
ly two months after heavy precipitation
events.
Chemical constituents contained in the
treated wastewater applied to the Han-
cock farm were removed by the soil-crop
matrix from percolate water. Increases in
ground-water chemical parameters ap-
peared to be associated with deep per-
colation of surface runoff contained in
moats and excavation pits constructed to
contain surface runoff. Existing salt and
nitrate deposits within the soil profile were
leached with percolate to the ground
water; thereby causing increases in nitrate
and total dissolved solids (TDS) levels in
several wells.
In general, no significant changes in
trace metals or priority organic pollutants
occurred in the ground water during the
monitoring period. Based on values cited
in literature, trace elements posed no
public health problems.
Salt accumulation occurred in the upper
183 cm of the soil profile. As expected,
salt accumulations were directly propor-
tional to mass loadings from irrigation.
Insufficient water was applied (less than
21 cm in 1982 and less than 50 cm in
1983) to leach salts below the root zone.
Exchangeable sodium percentage in-
creased from two to six percent in the top
30 cm of soil during the period from
February 1982 to October 1983.
Cotton and grain sorghum (milo) were
the primary crops grown on the Hancock
farm in 1980, 1981 and 1983. Due to
severe weather in 1982, sunflowers, soy-
beans and grain sorghum were planted as
alternative crops to cotton. While milo
yields were low due to late planting and
trifluralin damage, sunflower and soybean
yields were average for the High Plains
area of Texas. An improvement in cotton
crop production occurred in 1983. With
irrigation of effluent, the cotton yields for
the farm were 48 percent greater than the
Lubbock County average. Cotton yields for
1983 may have been limited by possible
nutrient shortages, bollworm infestation,
and cool weather during late growing
season. Cotton production in 1983 ranged
from 353 to 740 kg/ha.
Amortized system construction cost
over a 20-year period at ten percent an-
nual interest rate would be §167/1,000
m3 per year ($0.63/1,000 gal). With 85
percent federal cost sharing, amortized
construction cost would have been re-
duced to $25/1,000 m3/yr ($0.10/1,000
gal). Inclusion of land cost would have in-
creased annual capital cost by 24 percent.
Total operation and maintenance (O & M)
costs associated with the Lubbock Land
Treatment System Expansion were
$156/1,000 m3 ($0.59/1,000 gal) in 1982
and $139/1,000 m3 ($0.53/1,000 gal) in
1983. The City of Lubbock bore $71/1,000
m3 of the total 0 & M cost in 1982 and
$58/1,000 m3 in 1983. The farmer's por-
tion of the 0 & M was $85/1,000 m3
($0.32/1,000 gal) and $81/1,000 m3
($0.31/1,000 gal) in 1982 and 1983,
respectively. The economic balance of
cost expended and revenues received
showed a net negative balance each year
during the project period (1980 through
1983) ranging from $701,661.81 (1981) to
$1,103,687.57 (1982). Net costs were
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$267.35/1,000 m3 ($1.00/1,000 gal) in
1982 and $161.28/1,000 m3 ($0.61/1,000
gal) in 1983. Crop revenues offset costs
by 18 and 47 percent of total costs in
1982 and 1983, respectively.
Spray irrigation of unchlorinated
wastewater piped from the treatment
plant was a more substantial source of
aerosolized microorganisms than spray ir-
rigation of wastewater stored in reservoirs.
Enteroviruses were regularly recovered in
the aerosol at 44 to 60 m downwind of
irrigation with piped treatment plant
wastewater. The geometric mean
enterovirus density in the downwind air
was 0.05 pfu/m3, although a much higher
density (17 pfu/m3) was sampled in
August 1982. In addition, fecal strep-
tococci levels were detected at least 300
m downwind, and levels of fecal coliforms,
mycobacteria and coliphage were isolated
at least 200 m downwind. Organism levels
downwind were also significantly higher
than background levels in ambient air out-
side of participants' homes: fecal coliform
levels were higher beyond 400 m down-
wind, mycobacteria and coliphage levels
to at least 300 m and fecal streptococci
levels to at least 200 m.
The results indicate that a general
association between exposure to irrigation
wastewater and new infections existed,
especially for 1982 when there was ex-
posure to higher levels of microorganisms
via wastewater aerosol. Poliovirus 1 sero-
conversions were probably related to
wastewater aerosol exposure during the
spring of 1982, even when the effects of
polio immunizations were controlled.
However, even during 1982, the strength
of association remained weak and fre-
quently was not stable. Wastewater of
poor quality from the pipeline, comprised
much of the irrigation water in 1982. Of
the many infection episodes observed in
the study population, few appear to have
been associated with wastewater aerosol
exposure, and none resulted in serious
illness.
The lack of a strong, stable association
of clinical illness episodes with the level
of exposure to irrigation wastewater in-
dicates that wastewater spray irrigation
produced no obvious disease during the
study period. However, when more sen-
sitive indicators of infection were used, the
evidence indicates an association existed,
especially for 1982. A particular concern
from a public health standpoint is the
evidence that the poliovirus 1 seroconver-
sions were related to wastewater aerosol
exposure during the spring of 1982, even
when the effects of polio immunizations
were controlled. Because of the low
prevalence of poliovirus antibody observed
during the baseline period, the study
population was immunized, and thus was
probably better protected against polio
than other rural populations. High concen-
trations of both bacteria and enteric
viruses were observed in the 1982 poor
quality wastewater applied as received via
pipeline directly from the Lubbock sewage
treatment plant. Exposure would have
been reduced by using wastewater from
the reservoirs for irrigation rather than ir-
rigating directly from the pipeline.
Annual hydraulic loading rates up 3 m
ha/ha yr did not adversely affect cotton,
grain sorghum, and alfalfa crop produc-
tion. Highest alfalfa yields were obtained
in test plots irrigated with 365 and 434
cm ha/ha yr. Total dissolved solids and
associated sodium salts were leached
beyond 91 cm soil depth within plots ir-
rigated with 61 cm of treated sewage per
year or greater. Bermuda yields were
limited by transport of macro and micro
nutrients past the root zone.
Soybeans with a relatively shallow root
system, produced highest yields with
more frequent irrigation (i.e., one irrigation
per week). Soybeans were unable to
develop a deep root system to utilize
deeper soil moisture during periods of
water stress (one irrigation every four
weeks or one irrigation every eight weeks);
consequently, crop yields were reduced.
During long periods between irrigation
events, the deep root system developed by
grain sorghum enabled the plant to utilize
available soil moisture and inorganic
nitrogen at greater depths. Highest grain
sorghum production was achieved in plots
irrigated 61 and 122 cm/yr at application
frequencies of once every four weeks and
once every eight weeks.
Increasing the quantity of water applied
to a crop transports sodium salts deeper
into the soil profile. Soybean seed and
stalk analysis indicated leaching of sodium
from the root zone commenced almost im-
mediately at the 122 cm/yr hydraulic
loading. At the 61 cm/yr loading, irrigation
events must occur at intervals of two
weeks or longer to promote leaching of
sodium. Practically no leaching occurred
even at the one application per eight
weeks frequency at the effluent loading of
31 cm/yr. With the shorter growing season
experienced in 1982, soybeans may have
had a higher water consumption rate than
the grain sorghum due to the crop's
maturity. Higher water requirement of soy-
beans in conjunction with its shallow root
system may have caused higher sodium
accumulations in the upper 61 cm than
observed in grain sorghum test plots.
-------
D. B. George, N. A. Klein, and D. B. Leftwich are with Lubbock Christian College
Institute of Water Research. Lubbock. TX 79407; D. E. Camann, H. J. Harding, K.
T. Kimball, and R. L. Mason are with Southwest Research Institute. San
Antonio, TX 78284; N. L. Altman, P. J. Graham. R. L. Northrup. and C. Becker
Popescu are with University of Illinois at Chicago, Chicago. IL 60680; M. N.
Guntzel is with University of Texas at San Antonio, SanAntonio, TX79285;B. E.
Moore and C. A. Sorber are with University of Texas at Austin. Austin, TX
78712; R. B. Harrist and A. H. Holguin are with University of Texas School of
Public Health, Houston. TX 77025; and B. J. Claborn, Ft. H. Ramsey. andR. M.
Sweazy are with Texas Tech University, Lubbock, TX 79409.
Lowell E. Leach. Jack L. Witherow, H. George Keeler. Curtis C. Martin, and
Walter Jakubowski are the EPA Project Officers (see below).
The complete report consists of five volumes entitled "The Lubbock Land
Treatment System Research and Demonstration Project:"(Set Order No. PB
86-173580/AS; Cost $128.50, subject to change).
"Volume I. Demonstration/Hydrogeologic Study," (Order No. PB 86-173598/
AS; Cost $46.95. subject to change).
"Volume II. Percolate Investigation in the Root Zone," (Order No. PB 86-
173606/AS; Cost $16.95. subject to change).
"Volume III. Agricultural Research Study." (Order No. PB 86-173614/AS;
Cost $22.95, subject to change).
"Volume IV. Lubbock Infection Surveillance Study (LISS)," (Order No. PB
86-173622/AS; Cost $46.95, subject to change).
"Volume V. Executive Summary," (Order No. PB 86-173630/AS; Cost
$16.95, subject to change).
The above reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
. S. GOVERNMENT PRINTING OFFICE:1986/646 116/20815
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $30O
EPA/600/S2-86/027
0000329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 & DEARBORN STREET
CHICAGO IL 60604
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