Development and application of crop water stress index for scheduling irrigation in cotton (Gossypium hirsutum L.) under semiarid environment

Studies were conducted to determine the crop water stress index (CWSI) for irrigation scheduling of cotton crop under irrigated semiarid environment. The investigations were carried out at the Post Graduate Agriculture Research Station (PARS), University of Agriculture, Faisalabad (UAF), Pakistan (latitude 31 degrees 25'N, longitude 73 degrees 09'E and altitude 184.4 m from sea level), during summer season 2006. Five treatments with different irrigation conditions were managed under randomized complete block design (RCBD). These treatments included T-0 no irrigation except rainfall (NI); T-1 irrigation at vegetation stage (VS-1); T-2 irrigation at vegetation and flowering stage (VS-1 + FS-1); T-3 irrigation at vegetation, flowering and boll formation stage (VS-1 + FS-1 + BF-1) and T-4 irrigation at vegetation, flowering, boll formation and at late stage (VS-1 + FS-1 + BF-1 + LS-1). Lower and upper baselines were developed for the cotton crop. For developing upper baseline (fully water-stressed), cotton was grown as a separate treatment where irrigation application was restricted. Lower baseline was developed by using canopy and air temperatures attained on clear sky days with 5-8 days of irrigation and rainfall application to field. The seasonal CWSI values for each irrigation treatment were calculated as the average for the entire season. The mean value of CWSI for treatment T-0, T-1, T-2, T-3 and T-4 were 0.76, 0.60, 0.42, 0.28 and 0.24, respectively. The trends in CWSI were consistent with moisture content in the soil. The relationship between yield and seasonal mean CWSI values was primarily linear: Y = -2320.3CWSI + 3048.5 (r(2) = 0.95, r = 0.97, SE = 0.05, P<0.01). This relation can be used to predict the yield of cotton, and data thus generated will be beneficial for further research.