Choosing and Managing an Irrigation System for Sustainability

Larry Schwankl

Highly efficient irrigation is a major component of sustainable irrigated agriculture. Irrigating efficiently means applying only the amount of water that can be beneficially used. The major beneficial use is satisfaction of the crop’s water needs (evapotranspiration = ET). Other beneficial water uses can include salinity control or frost protection.

Efficient irrigation is achieved by: 1) applying the correct amount of water at the correct time, and 2) applying the water uniformly across the field. Inefficiencies in irrigation result when water is lost to deep percolation (water passing below the crop’s root zone) or to runoff from the field which is not reused. Determining the correct amount of water to apply and when to apply it is referred to as irrigation scheduling. The management tools available for irrigation scheduling include evapotranspiration (ET) scheduling, soil-based scheduling, and plant-based scheduling. Any or a combination of these methods can be very effective, but they all require a commitment to manage irrigation water applications.

Knowing when and how much water to apply is important, but irrigation uniformity is the key to high irrigation efficiency. If the irrigation system applies water non-uniformly, the irrigation water manager is faced with: 1) over-irrigating portions of the field to ensure that even the field section receiving the least amount of water is adequately irrigated, or 2) under-irrigating portions of the field. The first option obviously leads to irrigation inefficiency, while the second option appears efficient on a field average basis – but can still result in deep percolation at the high application portions of the field. There is simply no way of getting around the need for a uniform irrigation system in order to achieve high irrigation efficiency.

How do we get a uniform irrigation system? One way is to pay for it. Well-designed microirrigation and sprinkler irrigation systems use hardware (pipes, tubing, sprinklers, and microirrigation emitters) to deliver irrigation water uniformly to all portions of the field. These systems can achieve high irrigation efficiencies when combined with high quality irrigation water management, but these systems are expensive, often costing $1000/acre or more and requiring energy to pressurize the water. In the case of microirrigation systems, they may also require a high degree of management and maintenance to keep them operating properly.

Achieving high irrigation uniformity and efficiency with flood irrigation systems (furrow, border, and basin irrigation) can be difficult. Ideally, water should be applied to the soil for the same amount of time at all spots in the field. This is very difficult to do with a flood irrigation system, and it is most difficult to do on soils with a high infiltration rate (e.g. sandy textured soils). On soils with low infiltration rates (e.g. heavier textured soils), it may be possible to achieve high irrigation uniformities when field lengths are kept relatively short. The flood irrigation system must be designed to allow the irrigator to apply the correct amount of water (determined from irrigation scheduling) and still irrigate the entire field adequately.

In summary, a major component of making irrigation sustainable is to be as efficient as possible with the application of irrigation water. Irrigation water applications should match as closely as possible beneficial water requirements - crop water requirements being the major beneficial water use. To achieve high irrigation efficiency, the irrigation water manager must do a good job of irrigation scheduling, have a highly uniform irrigation system available, and then manage that irrigation system to apply the correct amount of irrigation water uniformly throughout the field.

Larry Schwankl, Irrigation Specialist
Cooperative Extension
University of California
235 Veihmeyer Hall – One Shields Ave.
Davis, CA 95616
Tel: (530) 752-0453

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