Crop water stress index for devising water efficient irrigation schedules for wheat crop

Development of irrigation schedules that lead to efficient use of water is imperative. For his, crop experiments were conducted in the humid sub-tropical climate region of western Uttar Pradesh, India where a plant-based index, Crop Water Stress Index (CWSI), has been derived for a crop season of wheat crop. Four irrigation regimes, two equipped drip irrigation and two with flood irrigation, of 25% MAD (drip), 50% MAD (drip), 50% MAD (flood) and a farmer’s field replication (flood) were experimented in the study. MAD is maximum allowable deficit that represents the soil moisture depletion at which irrigation was applied. Research-grade infrared thermometers were used for field measurements of crop canopy temperature. The empirical approach of CWSI is applied to formulate lower and upper baselines utilizing the air temperature humidity parameters and CWSI values for wheat crop for the pre-heading and post-heading stages are derived. Mean CWSI values for irrigation regimes are found out as 0.3, 0.12, 0.29 and 0.32 for 25% MAD (drip), 50% (drip), 50% (flood) and a farmer’s field replication (flood), respectively during the crop period with the higher values of CWSI representing more crop water stress. The highest water use efficiency (WUE) of 19.36 kg/ha-mm is observed for 50% (drip) irrigation treatment with a mean CWSI value of 0.12. The farmer’s field replication, which corresponds to the lowest WUE, has by-far the highest value of mean CWSI during the post-heading stage. The use of a plant based index rather than the conventional soil moisture method can be a more effective method to determine water-efficient irrigation schedules.