Effect of water-saving irrigation on rice yield and water use in typical lowland conditions in Asia

With decreasing water availability for agriculture and increasing demand for rice, water use in rice production systems has to be reduced and water productivity increased. Alternately submerged-nonsubmerged (ASNS) systems save water compared with continuous submergence (CS). However, the reported effect on yield varies widely and detailed characterizations of the hydrological conditions of ASNS experiments are often lacking so that generalizations are difficult to make. We compared the effects of ASNS and CS on crop performance and water use, at different levels of N input, in field experiments in China and the Philippines, while recording in detail the hydrological dynamics during the experiment. The experiments were conducted in irrigated lowlands and followed ASNS practices as recommended to farmers in China. The sites had silty clay loam soils, shallow groundwater tables and percolation rates of 1-4.5 mm per day. Grain yields were 4.1-5.0 t ha(-1) with 0 kg N ha(-1) and 6.8-9.2 t ha-1 with 180 kg N ha(-1). Biomass and yield did not significantly differ between ASNS and CS, but water productivity was significantly higher under ASNS than under CS in two out of three experiments. There was no significant water x N interaction on yield, biomass, and water productivity. Combined rainfall plus irrigation water inputs were 600-960mm under CS, and 6-14% lower under ASNS. Irrigation water input was 15-18% lower under ASNS than under CS, but only significantly so in one experiment. Under ASNS, the soils had no ponded water for 40-60% of the total time of crop growth. During the nonsubmerged periods, ponded water depths or shallow groundwater tables never went deeper than -35 cm and remained most of the time within the rooted depth of the soil. Soil water potentials did not drop below -10 kPa. We argue that our results are typical for poorly-drained irrigated lowlands in Asia, and that ASNS can reduce water use up to 15% without affecting yield when the shallow groundwater stays within about 0-30 cm. A hydrological characterization and mapping of Asia's rice area is needed to assess the extent and magnitude of potential water savings. (C) 2003 Elsevier B.V. All rights reserved