Field evaluation of the components of soil water balance model

A two-year field study was conducted on sandy loam and silty clay loam at Punjab Agricultural University, Ludhiana to study the effect of puddling (residual) and water management practices on crop growth and water balance components in wheat following rice. Treatments included two irrigation regimes - irrigation at IW/PAN-E ratio of 0.6 (I_0.6) and 1.2 (I_1.2) in the main plots and three residual puddling levels - P₀ (no puddling), P₂ (two discing + planking) and P₄ (four discing + planking) in subplots. Water balance model was used to access the components of field water balance in wheat. Simulated water loss from the soil [sum of soil evaporation (E), plant transpiration (T) and drainage (D) down to profile] matched well with measured values [sum of profile water depletion from seeding to harvest (DS), rain (R) and irrigation (I)] for seasonal water loss ranging between 36.6 to 43.9 cm. Root mean square of deviations (RMSD) of simulated loss from the measured values was 3.42 cm. Predicted soil water content was quite close to the measured in all layers for most of the crop season with RMSD of 4.2 and 2.6% under sandy loam and silty clay loam, respectively. Accumulated transpiration was increased and soil evaporation decreased with puddling and irrigation. Deep drainage down the root zone was more in I_1.2 irrigation treatment on both the soils during two years. Irrigation as well as puddling significantly increased the grain yield of wheat. In sandy loam water use efficiency was increased with puddling levels in two irrigation regimes during both the seasons. However, in silty clay loam increase in water use efficiency with puddling in two irrigation regimes was only during 1996–97. Harvest time, relative dry matter yield and estimated seasonal relative transpiration was fitted to a linear function.