Evaluation of Crop Water Stress Index (CWSI) for Irrigation Scheduling of Wheat in Sub- Humid Conditions of India

This research explores the use of the Crop Water Stress Index (CWSI) for planning irrigation in wheat (Triticum aestivum L.) under field conditions in Roorkee, India, during the 2018–19 and 2019–20 growing seasons. Five different irrigation treatments were applied: T1 (no water stress), T2 (maximum stress), T3 (10% soil moisture depletion), T4 (30% depletion), and T5 (50% depletion). The difference between canopy and air temperature (Tc – Ta) and the vapor pressure deficit (VPD) were utilized to create baselines for estimating CWSI. Regression analysis showed strong negative correlations, with R² values of 0.95 and 0.88 for the pre- and post-heading stages in 2018–19, and 0.99 and 0.96 in 2019–20, respectively. Average CWSI values ranged from 0.07 (T1) to 1.00 (T2). Grain yield varied significantly, with a peak of 2375 kg ha⁻¹ (T3) and a low of 325–375 kg ha⁻¹ (T2), while the amount of irrigation applied ranged from 390.5 mm (T1) to 150.5 mm (T2). The highest water use efficiency (WUE) of 2.71 and 2.65 kg ha⁻¹ mm⁻¹ was recorded under T3 in both years. A quadratic relationship between WUE and CWSI suggested an optimal range at CWSI ≈ 0.3–0.4, where yield sustainability and water productivity were maximized. Beyond this point, both yield and WUE decreased sharply. These findings confirm that CWSI is an effective tool for monitoring crop stress and can be used to optimize irrigation scheduling for wheat, allowing for water savings of up to 30% without significant yield losses.