&ER&
United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-82-071 Sept. 1982
Project Summary
Demonstration of Irrigation
Return Flow Water Quality
Control in the Mesilla Valley,
New Mexico
Robert R. Lansford, Peter J. Wierenga, Theodore W. Sammis, and Bobby J.
Creel
The general objective of this project
was to demonstrate the effect of
alternative water management prac-
tices on the quality of drainage return
flow and soil salinity in the Mesilla
Valley in southern New Mexico. The
project area consisted of a 4-acre test
site and a 450-acre demonstration
site. The feasibility of irrigating at or
near 100 percent irrigation efficiency
with water of medium salinity (1200
ppm), while maintaining optimum
crop yield over many years, was
demonstrated on the 4-acre test site at
the New Mexico State University Plant
Science Farm. At the 450-acre Dem-
onstration Farm, a combination of
present-day irrigation technology
showed how, through modern water
management, return flow quality and
quantity can be improved. In addition,
an economic analysis was performed
to determine the economic feasibility
of the water management practices
demonstrated. The economic analyses
were made based on the assumption
that valley-wide implementation of
demonstrated water management
practices would result in reduced
return flows and salinity at levels
found in the demonstration area.
Irrigation efficiency and irrigation
interval had a significant effect on
chloride concentration of saturation
extracts of samples taken from the
rooting depth of surface irrigated
plots. In addition, there were signifi-
cant increases in the salt content of
the soil irrigated for five years with a
trickle system, but the trickle plots
yielded six percent more lint cotton on
25 percent less water than did the
surface irrigated plots with essentially
no difference in lint quality.
The results of this study indicated
that by using irrigation scheduling,
farm irrigation efficiency can be
increased by 13 to 23 percent.
However, field irrigation efficiency
was found to vary from 80 percent
down to 35 percent regardless of type
of crop or field size. Trickle-irrigation
of a 1.3 hectare pecan orchard
resulted in irrigation efficiencies near
100 percent with apparent above
average yields.
Economic analysis of proposed
alternative water management sys-
tems for the Mesilla Valley indicated
that irrigation scheduling service
(ISS) reduced irrigation water use by
17 to 24 percent while net returns to
land risk increased by 5 to 9 percent. A
combination of ISS and sprinkler-
irrigation of vegetable crops for seed
germination resulted in the highest
net returns to land and risk with only
minor savings in irrigation water use.
ISS and trickle-irrigation management
practices only added marginal water
savings when compared with ISS, but
net returns would be reduced drasti-
cally.
ISS could reduce irrigation return
flows to the R io Grande from 30 to 36
percent and the salt load to the river by
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38,000 to 42,000 tons annually. ISS
plus sprinkler could reduce irrigation
return flows by an additional 4 to 5
percent and the salt load by an
additional 4,000 to 5,000 tons annu-
ally. ISS and trickle-irrigation could
reduce return flows 7 to 16 percent
below the ISS alternative and the salt
load in the river by 9,000 to 23,000
tons annually.
This Project Summary was developed
by EPA's Robert S. KerrEnvironmen-
tal Research Laboratory, Ada, OK, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information
at back).
Introduction
The quality of irrigation return flow
represents a major problem in the
western United States. The water of the
Upper Rio Grande has been reported as
a classic example of water quality
degradation due to irrigation. Mineral
pollution is the most serious problem in
the Upper Rio Grande Basin. The
problem is serious because the basin is
approaching, or has approached, condi-
tions of full development and utilization
of the available water resources. There
is a progressive increase in the concen-
tration of total dissolved solids and the
percent sodium from the upper to the
lower sampling stations in the Upper
Rio Grande Basin. The large increase in
dissolved solids in the river along the
irrigated areas is, to a large extent, due
to the concentrating effect of irrigation.
Almost all of the valley land in the
Upper Rio Grande Basin has a high
water table. Where irrigation exists,
drainage canals divert water from the
"near-surface aquifers" into the Rio
Grande. In the Mesilla Valley, as in
many other areas, high equilibrium
salinity concentrations are known to
exist in the near-surface aquifer. The
key to achieving a reduction in salt
loading is to lower the groundwater
levels. The most effective means for
lowering groundwater levels is to
reduce the source of groundwater
flows, which can be accomplished by
reducing seepage losses through lining
canals and laterals, or by reducing deep
percolation losses resulting from ex-
cessive irrigation by improved on-farm
water management practices.
The U.S. Senate Select Committee
(1961) and a U.S. Water Resources
Council Study (1968) reports estimated
that the Upper Rio Grande and Pecos
Basins were the shortest on water in
relation to projected future demands of
any basin in the continental United
States. The Water Resources Council
study identified the major problems as
water deficiencies, groundwater storage
depletion, and poor water quality
because of mineral pollution. The past
15-year average inflow to Elephant
Butte Reservoir is only about 65 to 70
percent of the long-term average
inflow. Thus, a program for reduction of
mineral pollution loading is urgently
needed in order to protect existing
water uses from mineral quality degra-
dation during low-flow periods, and to
prevent the serious restriction of future
basin-wide economic development.
Conclusions
Field Plot Demonstration
In 1976 and 1977 irrigation treatment
(efficiency and irrigation interval) had a
significant effect on the electrical
conductivity (EC) and chloride concen-
tration of saturation extracts of samples
taken from the rooting depth jn the
surface-irrigation plots. ECe and chloride
concentrations were significantly higher
for the plots irrigated near 100 percent
efficiency. However, irrigation treat-
ments did not have a significant effect
on ECe and chloride concentration of
soil below 150 cm, indicating that
improving irrigation efficiency has no
immediate effect on the quality of
percolation water.
Based on the chloride concentrations
of soil water percolating below the root
zone in the surface-irrigated plots,
leaching fractions of 0.14, 0.11 and
0.09 were obtained for the planned 80,
90 and 100 percent efficiency treat-
ments, respectively.
Surface-irrigation treatments had no
significant effect on cotton yield at the
five percent level of probability during
1972 through 1977. However, yields
decreased with increased irrigation
efficiency, except in the 50 percent
depletion (two weeks irrigation interval)
treatment. For the conditions of the
experiment, less frequent irrigations
with some leaching provided the highest
cotton yields.
There was a significant increase in
the salt content of the soil irrigated for
five years with a trickle system, espe-
cially in the 30 to 130 cm depth range. The
salinity increase was 25 percent for the
plots irrigated at 0.2 bar and 100
percent for the plots receiving 25
percent less water than the 0.2 bar
treatment.
Salt contents were significantly
higher in the soil between the trickle
lines than below the trickle lines to a
depth of 50 cm. Below 50 cm, there
were no significant differences in salt
content below or between the trickle
lines.
Averaged over five years and all
treatment, the trickle-irrigated plots
yielded six percent more lint cotton than
the surface-irrigated plots, with no
difference in line quality. An average of
35 percent more water (irrigation and
rain) was applied to the surface-
irrigated plots than to the trickle-
irrigated plots.
There was a strong inverse correlation
between flow of water in the Del Rio
Drain and its quality. The average EC of
the water in the Del Rio Drain from
1972 to 1978 was very close to the
average EC of the water from 1921 to
1936, indicating a near equilibrium of
the valley along the Del Rio Drain.
Demonstration Farm
Using irrigation scheduling on the
450-acre Demonstration Farm, the
yearly irrigation efficiency was 63
percent, a 13 to 23 percent increase
over the 40 to 50 percent irrigation
efficiency considered normal for the
Mesilla Valley.
The results show that the overall
irrigation efficiency of the Demonstration
Farm (63 percent) was above average
with irrigation scheduling, although
large variations from field to field were
noted ranging from 80 percent to 35
percent. Field irrigation efficiencies did
not correlate with the type of crop being
grown or field size.
The canals at the measurement sites
had very low seepage losses. In the
main canal, the maximum loss per 1000
meters of canal ranged from 3 percent
down to 0.2 percent, depending upon
the flow in the canal. Seepage losses
from the farm ditches measured were
1.1 to 5.6 percent of the total applied
water over the growing season.
Trickle-irrigation of the pecan orchard
resulted in irrigation efficiencies of
nearly 100 percent.. Additional mea-
surements are necessary to determine
if any detrimental effects would occur
from salt accumulation due to the
continued use of trickle-irrigation with
efficiencies approaching 100 percent.
There was a negative correlation
between groundwater height on the
Demonstration Farm and a drain flow
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increase through the farm during 1977.
During 1975 and 1976, drain flow
measurements at two locations did not
show a statistical increase or decrease
in the flow through the Demonstration
Farm. Consequently, changes in drain
flow did not correlate to changes in
groundwater height. Short-term changes
in flow rates during the growing season
may be influenced more by the amount
of excess surface water being returned
into the drains than by the height of the
groundwater table.
The Effect of irrigation scheduling on
drain flow quantity was not detectable.
However, irrigation scheduling at the
Demonstration Farm increased the
irrigation efficiency by approximately
13 percent.
Salinity of the drain water showed a
negative correlation with flow, decreas-
ing as drain flow increased in all years.
Groundwater quality at the sampling
points on the Demonstration Farm
indicated an increase in nitrate content
and a decrease in total salinity with
depth below the water table.
Economic Analysis
For the three water supply periods
(1967, 1973, and 1976) significant
quantities of groundwater could have
been saved (17 to 24 percent) while the
returns to land and risk could have been
increased by 4.8 to 9.2 percent by the
incorporation of irrigation scheduling
service (ISS). Irrigation return flows
could have been reduced by 30 to 36
percent and the salt load on the Rio
Grande reduced 38,000 to 43,000 tons
with the implementation of ISS.
The combination of ISS and sprinkler-
irrigation for vegetable crop seed
germination could add an additional
reduction of two to three percent in
irrigation water savings. Net returns to
irrigated agriculture would be expected
to decrease below that expected for ISS
in two of the three water supply periods
by 1.4 to 3.1 percent and only increase
by about 0.4 percent in above average
surface water supply period. Irrigation
return flows would decrease by an
additional four to five percent and the
salt load on the Rio Grande only be
reduced by 4,000to 5,000tonsannually.
The combination of ISS and trickle-
irrigation for orchards could significantly
reduce surface water use (6 to 15
percent) with increases in groundwater
(0.4 to 9 percent) above the ISS
alternative. However, significant de-
creases in net returns would be en-
countered. Irrigation return flows
would decrease by 7 to 16 percent
below the ISS alternative which trans-
lates to 9,000 to 23,000 tons of salt to
the Rio Grande annually.
A combination of ISS, sprinkler- and
trickle-irrigation management practices
would reduce surface supplied irrigation
water use by 6 to 16 percent and
groundwater use by 16 to 18 percent
below that of current irrigation practices.
The impact on net returns would vary
from a reduction of nine percent to an
increase of about one percent annually.
The reduction in irrigation return flows
could be 40 to 50 percent and the salt
load on the Rio Grande reduced 50,000
to 70,000 tons annually.
Recommendations
1. For maximum benefit of water
supplies in the Mesilla Valley, farm
irrigation systems should be de-
signed for minimum leaching.
2. Increased efforts are needed to
better define the actual water use
of crops in the Mesilla Valley, in
particular of pecan orchards.
3. Trickle-irrigation, though not eco-
nomical at present, can be used to
maintain or improve yields of cotton
with 25 percent less water. Demon-
stration projects on the use of
trickle-irrigation for vegetable pro-
duction in the Mesilla Valley are
recommended. Trickle systems
may be economically justified for
quality and marketing considera-
tions.
4. Increased efforts are needed to
further encourage the utilization of
irrigation scheduling service and
sprinkler-irrigation of vegetable
crops for seed germination in the
Mesilla Valley.
5. A combination of irrigation systems
should be investigated for seed
germination, i.e. trickle or sprinkler
and flood.
6. Equipment to measure applied
water to each field should be
incorporated in farm irrigation
systems to improve field irrigation
efficiencies.
7. Continued monitoring of the salinity
in the soil beneath the field sites
where irrigation scheduling is
practiced would help to determine
the long-range effect of increased
efficiency on salinity buildup.
8. Future studies should be directed
toward predicting the long-term
effects on the salt load in the Rio
Grande resulting from improve-
ments in irrigation efficiency in the
irrigated areas along the.Rio Grande
in New Mexico, and taking into
account continued use of ground-
water as well as increased urban
and industrial developments.
9. A detailed study of the hydrology of
the Mesilla Valley should be under-
taken to determine the effect of
mixing on the quality of ground-
water.
Robert R. Lansford. Peter J. Wierenga, Theodore W. Sammis, and Bobby J. Creel
are with the New Mexico State University, Las Cruces. NM 88003.
Arthur G. Hornsby is the EPA Project Officer (see below).
The complete report, entitled "Demonstration of Irrigation Return Flow Water
Quality Control in the Mesilla Valley, New Mexico," (Order No. PB82-255316;
Cost: $15.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada. OK 74820
4 US GOVERNMENTPfllNTINQOFFICE: 1982-559-017/0824
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Environmental Protection
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