The purpose of this study is to evaluate technical and economic feasibility of using Israeli
subsurface drip irrigation technology for growing rice in Texas. This report documents
three years of rice farming experiments conducted by Lower Colorado River Authority
(LCRA) and Netafim, an Israeli drip irrigation manufacturing company, using subsurface
drip irrigation system. This research was partially funded by the Texas-Israel Exchange
of the Texas Department of Agriculture.
Water is a key requirement for rice and traditionally irrigation meant flooding, a practice
that uses a substantial volume of water. As Texas’ economy develops, there are arising
alternative competing uses of limited water resources of the state. At some point other
water demands will create uncertainty whether the volume of water now used to irrigate
rice can be sustained. For over 20 years the LCRA has sought to develop water
conservation policies and use them to make rice irrigation more efficient, as required by
guidelines adopted by the Texas Water Commission in 1988.
As part of its water conservation effort, the LCRA investigated new technologies and
irrigation methods for rice, such as subsurface drip irrigation. For the past three years,
2001 to 2003, the LCRA, in collaboration with Netafim Texas A&M University,
experimented with sub-surface drip irrigation for rice. The results from the drip
experiment indicate that rice yield can be sustained or increased while saving at least 50
percent of the water. Economical analysis indicates that sub-surface drip irrigation is
beneficial both for rice farmers and the rest of the population of the state. From the state
perspective, adopting sub-surface drip irrigation will save irrigation water so more water
may become available to other uses. Figure 1 compares water consumption for
conventional irrigation and sub-surface drip irrigation in the Colorado, Wharton and
Matagorda counties, assuming Texas Water Development Board estimates1 to the year
2060; these numbers assume a 50 percent saving rate. The water that could be
potentially saved by installing sub-surface drip irrigation for rice, all rice farmed in the
Lower Colorado River Basin, is comparable to 2.3 times the 2000 water demand of the
City of Austin. Although this is an unrealistically ambitious expectation, implementing
such practice in only a fraction of all rice irrigated land could conserve large quantities of
water for meeting growing water needs of the state while proving reliable water supply to
more than 100 year old rice economy of Colorado, Wharton and Matagorda counties.
From the farmer’s perspective, sub-surface drip irrigation can yield net benefit for each
dollar of investment in drip equipment. Costs are based on installing subsurface drip
irrigation system at a cost of $500 per acre and assuming that the drip irrigation system
will last for 15 years. The benefits reflect only savings in water cost, assuming that
conventional water use is 5.25 acre feet per acre of farmed land and a market price of
$0.07 per pound of rice. If the savings in water and the increase in yield reflect the bestexperimental results (80 percent water reduction, 10 percent increase in yield), the total
benefits could be as much as $4.78 per dollar of investment.
In other words, drip irrigation could allow rice farmers to farm the same land, increase
production, save money, make more profit and reduce significantly the water use for rice
irrigation. Table 1 lists performance measures based on both optimistic and expected
scenarios for Texas.
The LCRA has sought to increase the availability of water for rice farming in Texas
because rice remains profitable and rice farmers continue to have reliable markets. The
rice market is growing because world rice demands are increasing while rice production
is decreasing in many countries. Texas rice continues to remain competitive because of
its good quality based on its grain size, taste and proximity to the Latin American market.
The use of subsurface drip irrigation requires the installation of infrastructure and capital
investment. Based on an economic analysis, the costs of subsurface drip irrigation may
be offset by the saving in water cost alone.
As urban activities expand and use more water, Texas water policy makers are
encouraging farmers to use irrigation methods that reduce water use and increase yield
in order to allow water to flow to other economic sectors. The LCRA, a water district that
manages the Lower Colorado River, is the owner and operator of three large irrigation
districts that have developed conservative water use technologies for rice irrigation. The
LCRA has sought to increase the reliability of irrigation water for rice farming because
irrigation is the largest single water user in the river basin today.
The LCRA water conservation policies and programs reflect the guidelines adopted by
the Texas Water Commission in 1988 for water conservation. Under the Texas Water
Code, holders of water rights permits may only apply water for beneficial uses. The
Texas state law defines “beneficial use” as use of the amount of water which is
economically necessary for a purpose authorized by law, when reasonable intelligence
and reasonable diligence are used in applying the water to that purpose.2
Any use of water in excess of “a reasonable duty of water for rice irrigation”3 can be
defined as a “non-beneficial” use of water. Any non-beneficial use of water at some point
could affect the water rights of the irrigation districts. In 1988, the Texas Commission on
Environmental Quality (TCEQ) adopted a standard of 5.25 acre-foot of water per acre of
rice cultivation as an expected volume.4 Also, the Texas Water Code states that
persons supplying state water for irrigation purposes shall charge the purchaser on a
volumetric basis. The TCEQ may direct suppliers of state water to implement
appropriate procedures for determining the volume of water delivered.5
Promoting water conservation in irrigation is a high priority for the LCRA as described in
the LCRA’s water conservation policy outlined in its document: “Board Policy Statement
WFC 505.00.”6 That policy is applied in the Water Management Plan7 and is supported
by Board policy statements.8 The 2000 LCRA agricultural water conservation policy
stated that the LCRA shall:
… support and assist public and private-sector initiatives to develop,
demonstrate, and apply cultivation and irrigation practices to improve on-farm
water use efficiency.
…assist with the transfer of information and technology for improving on-farm
water use efficiency from research to the producer.
… undertake maintenance, rehabilitation and management practices to minimize
water losses from LCRA irrigation water delivery systems.9
The LCRA has conducted rice water conservation studies for over 15 years. In 1987, the
LCRA initiated the “Less Water-More Rice” project to identify ways that farmers could
conserve water without reducing yields. This research determined that yields could be
increased by as much as 17 percent and water use reduced between 25 and 30 percent
by maintaining a shallow level of water in the fields and improving the methods of water
delivery into and through fields. A conversion to a volumetric pricing system started in
1990. The system went through trial years before it was adopted at the end of 1993.
In 2001, the LCRA began three experimental seasons testing subsurface drip irrigation
for rice farming. The section below describes that effort.
The Drip Irrigation Experiment
LCRA water conservation measures adopted for rice farming during the 1980’s and
1990’s allowed rice farmers to increase yield while reducing the average per acre water
use by around 25 percent. Further water use efficiencies might enhance the reliability of
irrigation water. In 2001 the LCRA began to examine the possibility of using subsurface
drip irrigation for rice. This research was conducted in collaboration with Netafim, an
Israeli drip irrigation manufacturing company. It involved experiments conducted at the
Texas A&M University Agricultural Research and Extension Center in Beaumont, Texas.
The Texas Department of Agriculture’s Texas-Israel Exchange program partially funded
this research. The research compared water uses and yields for conventionally flooded
and subsurface drip irrigation treatments.
Flood irrigation is the conventional method for rice irrigation and generally demands
more water than other irrigation practices. For example, in one recent study of the LCRA
rice irrigation districts, farmers used around 5.2 acre-feet of water per year per acre for
flood irrigation.11 One of the reasons farmers have used flood irrigation is that it
accomplishes multiple tasks. Flooding provides water for plant growth. It controls weeds
which can thus substitute for chemical herbicide and mechanical weeding. Flooding can
substitute for mechanical land leveling.
One of the rationales for considering subsurface drip irrigation is that such a system can
save water lost in direct evaporation, runoff and seepage. A well-designed drip system
will lose little water to runoff, deep percolation or evaporation. For such a drip system,
irrigation scheduling can be precisely managed to meet crop demands. In other words,
subsurface drip irrigation holds the promise of increased crop yields and quality while
reducing water use significantly. Also, by eliminating irrigation return flow all together;
sub-surface drip irrigation may help water quality of receiving water bodies.
Flood irrigation also produces methane, a greenhouse gas, as organic material in the
soil decomposes anaerobically. Methane gas produced from rice field contributes to the
global warming as shown in Table 2. Subsurface drip irrigation provides water to the
roots of the rice plant without cutting the oxygen supply from the atmosphere to the soil,
thus reducing anaerobic decomposition of soil organic matter. As in a natural wetland,
flooding a rice field cuts off the oxygen supply from the atmosphere to the soil, which
results in anaerobic decomposition of soil organic matter. Methane is a major end
product of anaerobic decomposition. It is released from submerged soils to the
atmosphere by diffusion and through roots and stems of rice plants.12
Subsurface drip irrigation has the potential to increase the rice crop yield while reducing
evaporation, runoff and seepage water losses, methane production, improved water
quality of receiving water bodies and reducing energy consumption by reducing the
amount of water pumped. Table 3 lists potential advantages of subsurface drip irrigation.
The section below describes three years of subsurface drip irrigation experiments during
the farming seasons of 2001, 2002 and 2003. These experiments were conducted byLCRA at the Texas A&M University Agricultural Research and Extension Center at
Beaumont, Texas. For the three years of the experiment, the approach was to establish
replicates for rice farming, use different irrigation methods in these replicates, and
compare yields of rice and water use among the different replicates. Table 4
summarizes the results from the experimental years. The experiments seek to isolate
the effect of factors other than drip irrigation such as planting time, presence of weeds,
use of pesticides, etc. so the only difference between the compared plots is the irrigation
method. Two categories of irrigation methods are used: conventional flooding, which
consists of flooding the field many times per season, versus subsurface drip irrigation,
which consists of supplying water to the plant near its roots and based on the plant need
for water. The experiments considered spacing options between drip lines for the
subsurface drip irrigation method.
During the first experimental season in 2001, two plots were established, each
consisting of three different fields: one conventionally flooded field, and two other fields
irrigated with subsurface drip lines at 16 and 32-inch spacing, respectively. When
subsurface drip lines are used, they were installed at a depth of seven inches. To
eliminate water stress on the rice plant, the treatment plots were monitored daily for
dryness. Approximately half inch of water is applied to the plot when the soil is dry for
two inches below the surface. The average volume of water used in 2001 in the
conventionally flooded treatment was 2.13 acre-feet of water per acre of rice cultivation.
The calculated amounts of water used were 0.35 and 0.39 acre-feet of water per acre of
rice cultivation for the 32-inch and 16-inch spacing treatments, respectively,
corresponding to about 16 percent and 18 percent of the water used in conventional
system, respectively.13 Mean yields were 2,895, 2,535, and 2,157 lb of rice per acre of
land for the 32-inch spacing, 16-inch spacing, and conventionally flooded treatment,
respectively. This indicates a higher yield of rice for the treatments where subsurface
drip irrigation is used for the experiment in 2001. Figure 2 illustrates the distribution of
the plots among the different irrigation treatment methods for 2001, 2002 and 2003
growing seasons. The plots established at year 2001 include the 16-, 32-inches and
flooding treatment methods. The same applies to the plots established in 2002. Some of
the plots established in 2003 have a 48-inches treatment method. The plots established
in prior years of the experiment were used subsequent years until the end of the
For the 2002 experiment, the experimental area was doubled, resulting in four
replications of each treatment as shown in Figure 2. The area included the 2001 two
replicates, referred to as the “old replicates”, and the two “new replicates.” A chemical
injector was added in year 2002 to fertilize the drip treatments. The amount of water
applied for the 16 and 32-inch drip treatments during 2002 were 1.45 and 1.56 acre-feet
of water per plot of rice cultivation, respectively. In 2002, Cypress, a medium season rice
variety required 2.72 acre-feet of water per acre of rice cultivation for the crop in
conventionally flooded plots.14 The flooded control showed the highest yields for 2002,
6,056 pounds of rice per acre of land, followed by 5,032 lb of rice per acre of land for the
32-inch treatment and 4,865 lb of rice per acre of land for the 16-inch treatment. The two
newer replications that were established for the 2002 season showed higher yields than
the replications which were established during the 2001 season. Rice farmers do not
usually farm the same plot for three years. The usual pattern is to farm a piece of land
one year and let it rest for two years. The reason is that rice farming tends to strip
nutrients from land, so that yields in subsequent years drop if lands are not left fallow.
One of the reasons for this yield drop is observed in the 2002-2003 experiments, couldbe such loss of nutrients from the land from the previous year’s experiment. In other
words, it is likely that the 2002 and 2003 yields would have been larger if plots were
farmed according to current fallowing practice.
Six replications were planted in 2003. Four of these, replications 1, 2, 3, and 4, were
planted on April 2, while remaining two were planted on April 16. Replication 6 consisted
of a 32-inch and a 48-inch drip treatment in addition to the conventionally flooded control
plot. Replications 1, 2, 3, 4 and 5 each consisted of a 16- and a 32-inch drip treatment in
addition to the conventionally flooded control plot.
This analysis considered replications 1, 2, 3 and 4 and replications 5 and 6 as two
separate sets because of the difference in planting dates. The mean water use in
replications 1, 2, 3 and 4 was 1.34 and 1.22 acre-feet per acre for the 16- and 32-inch
treatments, respectively. The mean water use per plot in replications 5 and 6 was 1.21,
1.31 and 1.38 acre-feet per acre for the 16-, 32-, and 48-inch treatments, respectively.
Conventionally flooded plots required 2.72 acre-feet of water per acre to bring rice to
maturity. The corresponding water savings exceed 50 percent for both the 16 and 32-
inch drip treatment plots.
Analysis of the 2003 yield data showed a slight difference among 16- and 32-inch
treatments and the control plot for replications 1, 2, 3 and 4. For these replications, the
16-inch treatment showed the highest yields of 3,721 lb of rice per acre of land followed
by the 32-inch treatment of 3,684 lb of rice per acre of land and the least yields
correspond to the flooded control 3,639 lb of rice per acre of land. A much larger
difference was observed between the 16-, 32- and 48-inch treatments and the flooded
control plot in replications 5 and 6. The flooded control showed the highest yields 4,785
lb of rice per acre of land, followed by the 16-inch of 4,293 lb of rice per acre of land, the
32-inch treatment of 4,066 lb of rice per acre of land, and the 48-inch of 3,794 lb of rice per acre of land.Experimental Conclusions
Preliminary results suggest that drip irrigation has the potential for large water savings
compared with conventionally flooded rice production. The results from the three years
suggest that at least a 50 percent water saving can be achieved while maintaining a
comparable rice yield.
During the first year of the study, both drip treatments produced more rice per acre than
the conventionally flooded rice treatment. Water use amounted to approximately 16
percent and 18 percent of the water used in conventional systems for the 32 and 16-inch
treatments, respectively. In other words, drip saved between 82 and 84 percent of the
water even as yield increased by 10 percent.
Lower yields were produced in the subsurface drip treatment plots in the 2002 season.
Water use amounted to approximately 47 percent and 43 percent of the water used in
conventional systems for the 32 and 16-inch treatments, respectively. Both the 16- and
32-inch treatments out-yielded conventional flooded rice production during the 2003
season in replications 1, 2, 3 and 4 while the reverse was observed for replications 5
and 6. In replications 5 and 6, the 48-inch treatment had the lowest yield. Water use
varied between 49 and 56 percent of the conventional use for the different treatmentsRecent experience is that a subsurface drip irrigation system costs in the order of $500
per acre to install. Netafim’s experience is that a subsurface drip irrigation system is
likely to last for 15 years. At these costs, with water savings either 50 or 80 percent, and
with yield either flat or increasing at 10 percent, economical analysis result in a cost
benefit-ratio could range from 0.88 to 4.78. Water price is assumed to be $33 per acrefeet
for rice irrigation and $105 per acre-feet for municipal and industrial use. The lower
benefit-cost ratio of 0.88 reflects a 50 percent water saving, a stable crop yield and
conserved water is marketed for rice irrigation. Increasing the assumed water savings to
80 percent, rice yield increase by 10 percent, rice price is assumed to be $0.07 per
pound and conserved water marketed to municipal and industrial customers may result
in benefit-cost ratio of as much as 4.78. Table 6 shows benefit cost ratios of various
scenarios of water conservation, yield impact and water markets. The analysis did not
take into account problems in implementing subsurface drip irrigation, such as many of
the farmers are tenant farmers and have little incentive to finance the system installation.
These figures do not incorporate the practice of leaving a field fallow for up to two years
due to nutrient depletion. The economic value of the use of subsurface drip irrigation
would be affected by the increase demand for water from many sectors of the economy.The following section discusses projected savings in cost of water for rice farming inview of the change in rice acreage due to changes in water availability and the rice
Conclusions and Future Work
Evidence from the experiment shows that subsurface drip irrigation can save water for
rice farming, while producing at least stable yield. Water savings of at least 50 percent
versus conventional method might loosen the pressure exerted now on rice farmers
because of water scarcity. The future of rice farming in Texas depends on the wise and
economical use of water. If the subsurface drip irrigation experiments continue, they can
be designed to provide more definitive answers to questions about cost effectiveness,
water efficiency and crop yields. Future work can address the potential reduction in
methane production and also can isolate the factors that affect yield. A larger-scale
experiment and the separation of factors, such as the effect of weeds, late planting,
pesticides, and farming the same plot year after year, should give better answers and
improve the prospect of rice farming in Texas. Although the LCRA’s three years of
experiment demonstrated economic feasibility of drip technology, it unanswered the
question of whether farmers would implement drip systems. Efforts should be made to
move from the “laboratory” scale of the current experiment to a full field trial of rice
farmed by drip irrigation. Such experiments would go far in resolving farmer’s
uncertainties regarding the value of investment in sub-surface drip irrigation for rice.
Advantages of Drip Irrigation
1 Subsurface drip irrigation may require less water since only a portion of
the soil surface is wetted. Thus evaporation losses can be reduced and
water use efficiency can be improved.
2 Subsurface drip irrigation may lead to increased crop yields which are
attributed to reduced fluctuations in soil water content and well aerated
plan root zone. Crops subjected to fewer water deficit conditions may also
3 Subsurface drip irrigation may reduce agrochemical application because
drip irrigation can deliver agrochemicals precisely in the wetted area
where active roots are distributed. Fertigation and chemigation via drip
irrigation facilitate the relatively uniform distribution of fertilizer and other
chemicals, thus reducing the amounts applied.
4 Subsurface drip irrigation may eliminate anaerobic decomposition of plant
materials and thus substantially reduce methane gas production. Methane
gas is considered one of the most potent global warming gases.
5 Since irrigation return flow will be totally eliminated, water quality of the
receiving water bodies could improve.