Crop water stress index for scheduling irrigation of Indian mustard (Brassica juncea) based on water use efficiency considerations

The study was conducted to determine the feasibility of canopy temperature based crop water stress index (CWSI) for scheduling irrigation of Indian mustard (Brassica juncea). Field crop experiments were conducted in Hamirpur, Himachal Pradesh (India) during three consecutive cropping seasons (2015, 2016 and 2017). The experimental field was divided into five plots with different levels of irrigation treatments based on depletion of total available soil water (TASW) in the crop root zone. The maximum soil moisture depletion (SMD) of TASW at 10%, 30% and 50%, full irrigated (non-stressed) and extremely dry (full stressed) conditions were maintained in respective plots. Relationships were developed between canopy-air temperature differential (T_C-T_A) and vapour pressure deficit (VPD) for non-stressed and fully stressed conditions to generate non-water-stressed baseline (NWSB) and maximum water-stressed baseline (MWSB) baselines for Indian mustard crop. The CWSI was computed for different SMD of TASW by using a proven empirical approach based on the baselines. The irrigation treatment corresponding to 30% SMD with a mean CWSI of 0.4 resulted in optimal yield and maximum water use efficiency. Results of the study suggest that established CWSI value can be used to detect stress and schedule irrigations for Indian mustard.