California scientists have developed a low-cost, high-tech system that predicts when flood irrigation will approach the end of an alfalfa field, then signals to turn it off – an innovation its developers say could save large amounts of water.

Grown on 1.1 million acres, alfalfa is the largest consumer of water among all crops in California, accounting for up to 27% of the state’s irrigation water use. It’s usually flood irrigated, often leading to overirrigation. Water is pumped in at the top of fields and flows down to the end. If the flow isn’t turned off before it reaches the bottom, some of it runs off.

The new system employs sensors to track the advance of water down a field, a model that predicts when water will reach the tail end of the field, and a cellular communications system that sends a cell-phone alert to the irrigator to turn off the water. In two seasons of field testing at the University of California, Davis, zero tailwater drained from trial fields compared with thousands of gallons of runoff from control fields.

“Under current practice, the alfalfa irrigator makes several trips to the field to determine when the wetting front has reached a certain distance from the bottom end of the check (irrigation channel) before turning off the irrigation,” writes Rajat Saha, assistant engineer for MBK Engineers in Sacramento, in the October-December issue of California Agriculture. “Even making several trips, the irrigator may miss the wetting-front advance, which results in excessive tailwater drainage.”

The system, developed by Saha and colleagues at UC Davis while he was a graduate student, was demonstrated last year at an alfalfa field day. The components are relatively inexpensive. The sensors (three per check) cost about $25 each; the data logger and modem, which can be moved from one location to another to reduce the initial investment, cost about $500 and $200, respectively.

If the new system, which may be commercially available in early 2012, were used for the typical five irrigations per season, up to 15,000 gallons of water per acre could be saved, Saha reports.

The research article, and the entire October-December issue, can be downloaded at californiaagriculture.ucanr.org.