Effect of field of view of canopy temperature observations on crop water stress index for irrigation scheduling

The monitoring of canopy temperature (Tc) helps to establish appropriate watering methods. This study calculates the crop water stress index (CWSI) for four irrigation regimes in semi-arid region, India. Plots 1, 2, 3, and 4 had soil moisture depletion of 50% (drip system), 25% (drip system), unregulated (farmer replicated flood system), and 50% (flood system) with irrigation. In this work, we examined the value of employing a portable infrared thermometer (IRT) to measure wheat canopy temperature (Tc) at two geographical locations. The IRT field of view is 51.28–5,128 cm2, or 10–100 cm from the canopy crown. The field of view change from 10 to 100 cm affects Tc and CWSI in the four irrigation treatments, ranging from 0.65 to 2.71% and 9.2 to 36.4%, respectively. The research found that increasing the IRT from 10 to 100 cm reduced slope by 5.7% and intercept values by 20.6% in lower baselines. The R2 for CWSI and soil moisture was 0.78 (10 cm) and 0.77 (100 cm). Drip-irrigated plots are more sensitive to IRT spatial resolution than flood-irrigated plots. The findings suggest that CWSI studies may benefit from specific sample methods for Tc evaluation.