Recent research questions whether drip irrigation is the most water-efficient way to irrigate crops. A New Mexico State resource economist's against-the-grain conclusion almost seems to defy logic by finding that drip irrigation ends up consuming more water than using a less efficient irrigation technique.

Frank Ward's research showed that drip irrigation increases crop yield but at a long-term water cost. Analyzing agricultural water use in the Upper Rio Grande River Basin, Ward found that drip irrigation consumes about half the amount of water as flood irrigation. Plants, however, use more of the water delivered via a drip system resulting in increase yields, with more water lost to evaptransporation. Also the increased yields encourage farmers to plant additional acreage further increasing water demand.

The biggest drawback, however, is that the efficiency of drip irrigation results in less overflow seeping back into aquifers or draining into area rivers or streams. Aquifers then receive less recharge, and less water is available to downstream users.

Ward does not deny the benefits of drip; he just doesn't count conservation among them. According to Ward a more accurate calculation of water use would look at the amount depleted from a basin and not just focus on the amount of flow from an irrigation pump.

Ward's conclusions question the efficacy of subsidies and policies adopted to encourage drip irrigation to conserve water. Water use might actually increase.

Published by the Proceedings of the National Academy of Sciences, the study was co-written by Manuel Pulido-Velazquez of the Polytechnic University of Valencia in Spain.