Irrigation requirements of rice under shallow water table conditions

Abstract

Irrigation experiments with wetland rice ( Oryza sativa L.) paddies for 2 years under shallow water table conditions showed that intermittent submergence 3 days after water vanished from the surface of the soil produced grain yields similar to continuous submergence. Whereas irrigation was necessary every 3 days in clay loam (S 1) and silty clay loam (S 2), and every 2 days in loam (S 3) under continuous submergence of 5 ± 2.5 cm, it was necessary only every 7 days in S 1 and S 2, and every 6 days in S 3, under intermittent submergence of 7.5 cm 3 days after water vanished from the soil surface. The intermittent submergence led to a 34–43% saving of irrigation water. Percolation losses were reduced by 36, 31 and 25% in S 1, S 2 and S 3, respectively, as compared to those under continuous submergence. Average percolation rate was 6.1–6.4 mm day −1 in S 1 and S 2, and 10.1 mm day −1 in S 3. Yields were higher in the better drained S 3 than in the poorly drained S 1 and S 2. Average ET ranged from 7.4 to 9.2 mm day −1 under continuous submergence and from 6.1 to 7.1 mm day −1 under intermittent submergence. The intermittent submergence produced 7.2–14.7 kg more grain per cm of ET than continuous submergence. Regression of seasonal water requirement (WR) on percolation ( P c) and ET, and grain yield on WR and ET was highly significant. Yield was better correlated with ET ( r = 0.92) than with WR ( r = 0.86).