Crop Water Stress Index for Scheduling Irrigation of Wheat Crop

The present study aimed to examine the relationship between canopy air temperature difference and vapor pressure deficit (VPD) in wheat crops under normal or nonstressfull conditions. The treatments were undertaken on five plots, having randomized block design (RBD), each maintained at different levels of soil moisture having full irrigation; no irrigation; and 10%, 30%, and 50% soil moisture. Then canopy air temperature difference was regressed against VPD to generate non-water stress and maximum water stress baselines, and the crop water stress index (CWSI) was computed using empirical approach-baseline methods at different soil moisture deficits. It was found that irrigation treatment at 30% soil moisture deficit yielded the maximum water use efficiency. The canopy air temperature difference and VPD resulted in linear relationships, and the slope (m) and intercept (c) for lower baseline of preheading and postheading stages of wheat crop were found as m=-2.371, c=-1.659; and m=-1.8952, c=-2.32, for the crop season of 2018-2019. Similarly, the non-water stress baseline equation in the season of 2019-2020 had m=-1.7184, c=-2.3009; and m=-1.8137, c=-1.9176 for preflowering and postflowering stages of wheat, respectively. The CWSI was determined by using the developed empirical equations for three irrigation schedules of different maximum allowable depletion (MAD) of available soil water (ASW). The developed CWSI may have the potential to improve irrigation scheduling of wheat in India. The study shows practical applications for enhancing wheat cultivation under varying soil moisture conditions. First, it recommends irrigating at 30% soil moisture deficit to maximize water use efficiency, aiding farmers in balancing crop yield and water conservation. Second, established relationships between canopy air temperature difference and VPD allow for the assessment of water stress. By utilizing regression equations, farmers can estimate the CWSI across soil moisture levels, guiding irrigation scheduling during critical growth stages. Third, the developed empirical equations enable real-time prediction of water stress. Monitoring the canopy air temperature difference and VPD offers insights into plant health, helping with informed decisions on irrigation and fertilization. Last, the findings are relevant for water-scarce regions like India, where tailored CWSI equations can be integrated into irrigation systems, promoting sustainable practices under a changing climate. This study may help farmers with practical tools for water-efficient wheat cultivation, fostering informed choices for sustainable agriculture, particularly in water-scarce regions.