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 in major rice growing areas is being threatened by water and energy related constraints. With these constraints in view, a 2 year field study was conducted to assess the effects of soil and water management practices on crop growth and water balance components in rice on sandy loam and silty clay loam soils of a semiarid subtropical environment of north India. Treatments included two irrigation regimes - continuous submergence (I-1) and intermittent submergence 2 days after drainage (I-2) in main plots, and three puddling intensities - no puddling (P-0), two discing + one planking (P-2), and four 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 puddling intensity from P-0 to P-2 or P-4 significantly increased leaf area index and dry matter production. There was no difference in these parameters in 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 water storage and daily water loss (ET + percolation). Coefficient of determination 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) and increased puddling intensity significantly decreased percolation loss on both the soils. Minimum percolation losses occurred in I2P4 treatment. Puddling intensity and intermittent flooding in combination resulted in higher water use efficiency. Early transplanted (10th June, high evaporativity) rice crop evapotranspired 11 cm more water than late transplanted (25th June, low evaporativity) crop without any significant change in grain yield. This study demonstrates that intermittent irrigation coupled with increased puddling intensity and shift of transplanting date toward low evaporativity period may help to check decline in water table and make the system energy-efficient. (C) 2001 Elsevier Science B.V. All rights reserved.