Simulating response of wheat to timing and depth of irrigation water in drip irrigation system using CERES-Wheat model

Conventionally wheat is irrigated at 4-5 growth stages with an irrigation water depth of 7.5 cm (conventional irrigation practice, CP) in North-Western India, resulting in wastage of water. An alternate yield sustaining cum water saving irrigation strategy is required. So, an experiment was conducted during 2014-15 and 2015-16 in split plot design at Punjab Agricultural University, Ludhiana, keeping three irrigation timings [three irrigations at crown root initiation, booting and milking (CBM); four irrigations at crown root initiation, tillering, booting and milking (CTBM) and five irrigations at crown root initiation, tillering, booting, milking and dough (CTBMD)] in main plots and four irrigation depth [50 mm at each stage in 2 splits (2SP); 75 mm at each stage in 3 splits (3SP); 100 mm at each stage in 4 splits (4SP); 75 mm at each stage conventionally (CP)] in sub plots, replicated four times. Five irrigations at CTBMD recorded significantly higher grain yield than 4 and 3 irrigations at CTBM and CBM, respectively. Four splits of 100 mm produced significantly higher grain yield than 2, 3 splits and CP (in pooled data). Crop evapotranspiration (ETc) and grain yield reduced by 14.5 and 13.4% in CBM than CTBMD. The reduction in ETc from 4SP to 2SP was 7-23% (15% for pooled data) with the highest (347-406 and 328-396 mm) in 4SP and lowest (319-374 and 258-298) in 2SP during 2014-15 and 2015-16, respectively. Similarly, 10.4% grain yield was decreased when irrigation applied at CP instead of 4SP. Though grain yield in 2SP and CP was similar, but there was water saving of 33.3% in 2SP as compared to CP. Therefore, application of 50 mm of irrigation water with drip can be recommended as a yield sustaining and water saving strategy and application of 100 mm of irrigation water at five growth stages using drip as a yield enhancing practice. The DSSAT model performed well (indicated by high correlation coefficient as well as low RMSE and MAPE) in simulating the days to anthesis (RMSE = 2.06 and 4.96 days; MAPE = 1.5 and 4.4%) and maturity (RMSE = 3.83 and 4.52 days; MAPE = 2.03 and 2.43%), LAI (r = 0.89 and 0.92; RMSE = 0.37 and 0.47; MAPE = 8.10 and 9.50%), grain yield (r = 0.92 and 0.97; RMSE = 154.60 and 160.90 kg; MAPE = 2.80 and 2.80%), biological yield (r = 0.67 and 0.58, RMSE = 584.9 and 691.0 kg; MAPE = 4.40 and 5.10%) and crop evapotranspiration (r = 0.95 and 0.96; RMSE = 9.20 and 16.20 mm and MAPE = 2.30 and 4.20%) during 2014-15 and 2015-16, respectively.