Farmers in West India and Pakistan face a conundrum. The decades-old warabandi (fixed turns) surface irrigation system, which supplies set amounts of water at predetermined times, does not always provide water when crops need it most. However, pumping groundwater, which offers farmers more control over when and how they irrigate, is expensive. IWMI is using laser and computer modeling technology to help farmers make more effective use of the water resources available to them.
“When you use more high-tech sprinkler or drip irrigation systems, you use pipes to convey water to the crops, and you apply it in a way that the soil is used to store water like a sponge,” says Arif Anwar, leader of IWMI’s Agricultural Water research group. “With surface irrigation, you use the field to both transport the water and store it. Trying to apply a constant depth of water over an area akin to a football pitch that is sloping and uneven, is the challenge many farmers face.”
The application of science and mathematics to make surface irrigation water more precise has been going on for decades; the stumbling block has been making it simple enough to project it out of academia and into practical use. There has been some success with using laser-guided land-leveling technology to improve the efficiency of water use in rice paddies irrigated with groundwater. However, less research has gone into applying similar technologies to gently sloping lands using gravity-fed surface irrigation methods, especially those constrained by the warabandi irrigation management.
High tech made easy
For several years, Anwar and his colleagues have researched how existing warabandi irrigation management in the Indus Basin might be used with the same precision as more high-tech irrigation methods. In a 2016 paper, they concluded that it would be relatively easy to achieve an improvement in irrigation performance, within current irrigation services, by smoothing soil surfaces and making changes to field layouts.
The researchers first used laser-guided grading to remove undulations from fields, while retaining their natural topographic slopes. They then entered field variables into the computer model WinSRFR, developed by the United States Department of Agriculture. These included field length, width and slope; properties of the soil, including the ease with which water could penetrate it; and the volume of water provided by the warabandi system, for how long and how often. The model then presented options on how farmers could control particular variables to optimize water use, for example, by increasing or decreasing the number of border strips or furrows.
“If you apply 50 millimeters of water, depending on crop type and weather, the crop will use it in 5 to 10 days; the farmer will need to replenish it after that,” says Anwar. “If you have lots of undulations or you don’t have the right slope, or the soil and geometry don’t match up, they’ll end up applying something like 150 millimeters of water to obtain the required minimum of 50 millimeters. So, they end up applying much more water, because it gets stuck in ponds and doesn’t travel. That’s what precision irrigation overcomes.”
More with less
Where farmers are relying solely on surface irrigation, using more of their allocation on one field means they have to leave more land fallow, thereby growing fewer crops than they otherwise could. Meanwhile, those using groundwater end up spending considerably more money than they need to on diesel to run their pumps. So, increasing the precision with which water is used has the potential to increase farm outputs and improve farmers’ livelihoods.
Laser levelling and grading equipment is widely available in Asia and can be hired relatively cheaply. Anwar and colleagues subsequently undertook research into the longevity of each grading action and concluded that the surface would remain smooth for 3 to 4 years before returning to its original condition. “The approach is very generic and can be applied in any place where surface irrigation prevails,” says Anwar. “But it is particularly appropriate for West India and Pakistan because of the inflexible nature of water supply under warabandi irrigation management.”
