Determination of crop water stress index for Kharif pearl millet in semi-arid environment

Achieving high grain yield depends on the ability to avoid water stress by continuous monitoring the crop during the growing season. This study investigates the use of infrared thermometry for monitoring water stress. A field experiment was conducted during kharif season of 2018 on pearl millet crop under rainfed condition. The experiment involved nine treatments composed of three dates of sowing (at onset of monsoon, after 10 d of onset of monsoon and after 20 d of onset of monsoon) and three cultivars (GHB 538, GHB 558 and GHB 744). Canopy temperature (T_c) was measured using infrared radiometer-IS 131 (Apogee instrument, USA) on daily basis in the afternoon hours (1400 h to 1430 h) along with psychrometric observations. Soil temperature, soil moisture, dry biomass, plant water content and plant height were also measured regularly. Pearl millet is drought tolerance crop but water stress condition during critical growth stage led to yield reduction. In CWSI, Upper base line (dT_u) was dT_u = 2.9°C which was relatively independent of vapour pressure deficit (VPD) and lower baseline was dT_l = -3.0468 (VPD) + 2.6409. Throughout season CWSI value remain between -1.47 to 1.26. A strong and negative correlation was observed between CWSI and soil moisture up to 30 cm depth in all treatments. The results revealed that pearl millet crop in similar climate and soil condition, should be irrigated at CWSI values 0.52 to avoid water stress. The relationship between percent available soil moisture (PASM) and CWSI was linear and useful to farmers for irrigation scheduling.