On-farm strategies for reducing water input in irrigated rice; case studies in the Philippines

Traditional transplanted rice with continuous standing water in Asia has relatively high water inputs. Because of increasing water scarcity, there is a need to develop alternative systems that require less water. This paper reports results of on-farm experiments in the Philippines to reduce water input by water-saving irrigation techniques and alternative crop establishment methods, such as wet and dry seeding. With continuous standing water, direct wet-seeded rice yielded higher than traditional transplanted rice by 3-17%, required 19% less water during the crop growth period and increased water productivity by 25-48%. Direct dry-seeded rice yielded the same as transplanted and wet-seeded rice, but can make more effective use of early season rainfall in the wet season and save irrigation water for the subsequent dry season. Direct seeding can further reduce water input by shortening the land preparation period. In transplanted and wet-seeded rice, keeping the soil continuously around saturation reduced yields on average by 5% and water inputs by 35% and increased water productivity by 45% compared with flooded conditions. Intermittent irrigation further reduced water inputs but at the expense of increased yield loss. Under water-saving irrigation, wet-seeded rice out-yielded transplanted rice by 6-36% and was a suitable establishment method to save water and retain high yields. Groundwater depth greatly affected water use and the possibilities of saving water. With shallow groundwater tables of 10-20 cm depth, irrigation water requirements and potential water savings were low but yield reductions were relatively small. The introduction of water-saving technologies at the field level can have implications for the hydrology and water use at larger spatial scale levels. (C) 2002 Elsevier Science B.V. All rights reserved.