APSIM-Oryza model for simulating paddy consumptive water footprints under alternate wetting and drying practice for Kharagpur, West Bengal, India

The alternate wetting–drying (AWD) irrigation method in paddy improves water productivity over conventional (CON) irrigation practice. However, the seasonal consumptive water footprints (CWFs) in AWD practice have not been studied extensively for different transplanting dates. In this study, the effect of transplanting date on CWFs of paddy was studied using field experimental data and a crop model for Kharagpur, West Bengal State of India. A popular medium duration of 115–120-day rice variety (IR-36) was selected and cultivated under AWD and CON irrigation practices during kharif (monsoon) and rabi (non-monsoon) seasons of 2015–2016 and 2016–2017 by adopting the existing transplanting dates (i.e. 16 July in kharif and 14 January in rabi). The crop model, APSIM-Oryza, was calibrated and validated using the field data and simulated the evapotranspiration (ETC), yield, and CWFs under AWD and CON practices. The APSIM-Oryza model was then used to simulate the effect of different transplanting dates on paddy yield, ETC, and CWFs. The seasonal water savings of AWD practice were 22–29% greater than those of CON practice, with a cost of 2–4% reduction in the yield. The APSIM-Oryza-simulated grain yield was found to be closely matched with the observed for both CON and AWD practices during calibration (R2 = 0.96, RMSE < 400 kg ha−1) and validation (R2 = 0.85, RMSE < 400 kg ha−1). The early transplanting in both kharif (i.e. 01 July) and rabi seasons (i.e. 15 December) of the study region can produce the maximum yield of 3.67 and 4.30 t ha−1, respectively, with the least CWF of 1221 and 914 m3t−1, respectively, for paddy under AWD practice. Therefore, the early transplanting in both experimental seasons was good enough for obtaining the maximum yield with minimum CWFs under AWD for this study region.