Modelling the effects of soil and water management practices on the water balance and performance of rice

Rice is a major food grain crop of the world. However, its sustainability i n major rice growing areas is being threatened by water and energy related constraints. With these constraints in view, a 2 year field study was condu cted to assess the effects of soil and water management practices on crop g rowth and water balance components in rice on sandy loam and silty clay loa m soils of a semiarid subtropical environment of north India. Treatments in cluded two irrigation regimes - continuous submergence (I-1) and intermitte nt submergence 2 days after drainage (I-2) in main plots, and three puddlin g intensities - no puddling (P-0), two discing + one planking (P-2), and fo ur discing + one planking (P-4) in subplots. Increase in puddling intensity significantly increased depth of puddle and decreased saturated hydraulic conductivity (K-s) of the puddled layer in both the soils. Increase in pudd ling intensity from P-0 to P-2 or P-4 significantly increased leaf area ind ex and dry matter production. There was no difference in these parameters i n P-2 and P-4 However, grain yield increased significantly with increase in puddling intensity. The modified SAWAH model satisfactorily simulated seasonal change in soil w ater storage and daily water loss (ET + percolation). Coefficient of determ ination between predicted and measured values of daily water loss was 0.96 in sandy loam and 0.86 in silty clay loam. Intermittent irrigation (I-2) an d increased puddling intensity significantly decreased percolation loss on both the soils. Minimum percolation losses occurred in I2P4 treatment. Pudd ling intensity and intermittent flooding in combination resulted in higher water use efficiency. Early transplanted (10th June, high evaporativity) ri ce crop evapotranspired 11 cm more water than late transplanted (25th June, low evaporativity) crop without any significant change in grain yield. Thi s study demonstrates that intermittent irrigation coupled with increased pu ddling intensity and shift of transplanting date toward low evaporativity p eriod may help to check decline in water table and make the system energy-e fficient. (C) 2001 Elsevier Science B.V. All rights reserved.