Determination of Crop Water Stress Index for Irrigation Scheduling of Chickpea (Cicer arietinum L.)

Abstract

This field experiment evaluated the relationship between canopy–air temperature difference and vapour pressure deficit (VPD) in chickpea (Cicer arietinum L.) to determine the crop water stress index (CWSI) for irrigation scheduling. The lower baseline showed a linear relationship with VPD, whereas the upper baseline was relatively independent of VPD. The upper baseline was dTᵤ = 6 °C, and the lower baseline was dTₗ = −1.9755 VPD + 2.1035. Under climatic and soil conditions similar to those of the study, irrigation could be scheduled at approximately CWSI 0.78 without farmyard manure (FYM) and 0.75 with 10 t ha⁻¹ FYM to avoid water stress. Seasonal mean CWSI was inversely related to seed, biomass and straw yields. Seed yield showed a negative linear relationship with seasonal mean CWSI (R² = 0.63), indicating the potential of CWSI for yield prediction. Yield attributes, including number of pods per plant, seed weight per plant, number of branches per plant and test weight, declined as CWSI increased. A strong negative correlation (−0.88) was observed between CWSI and soil moisture during the growing season. The relationship between CWSI and soil moisture was described by CWSI = −0.0932x + 1.4092 (R² = 0.77). These results indicate that canopy-air temperature based CWSI can support irrigation timing and crop water-stress assessment in chickpea under comparable conditions.