Field water management to save water and increase its productivity in irrigated lowland rice

Rice production in Asia needs to increase to feed a growing population wher eas water for irrigation is getting scarcer. Major challenges are to (i) sa ve water; (ii) increase water productivity and (iii) produce more rice with less water. This study analyzes the ways in which water-saving irrigation can help to meet these challenges at the field level. The analyses are cond ucted using experimental data collected mostly in central-northern India an d the Philippines. Water input can be reduced by reducing ponded water dept hs to soil saturation or by alternate wetting/drying. Water savings under s aturated soil conditions were on average 23% (+/- 14%) with yield reduction s of only 6% (+/-6%). Yields were reduced by 10-40% when soil water potenti als in the root zone were allowed to reach -100 to -300 mbar. In clayey soi ls, intermittent drying may lead to shrinkage and cracking, thereby risking increased soil water loss, increased water requirements and decreased wate r productivity. Water productivity in continuous flooded rice was typically 0.2-0.4 g grain per kg water in India and 0.3-1.1 g grain per kg water in the Philippines. Water-saving irrigation increases water productivity, up t o a maximum of about 1.9 g grain per kg water, but decreases yield. It ther efore does not produce more rice with less water on the same field. Field-l evel water productivity and yield can only be increased concomitantly by im proving total factor productivity or by raising the yield potential. Total rice production san be increased by using water saved in one location to ir rigate new land in another. IF this is not dent, a strategy of saving water at the field level potentially threatens total rice production at large. ( C) 2001 Elsevier Science B.V. All rights reserved.