Thermal Unit Consumption of Cotton under Different Sowing Conditions in South Western Punjab

To understand the impact of weather variability on phenological development and cotton yield efficiency, a field experiment was conducted during kharif 2015, 2016 and 2017, comprising three sowing dates (April 20, May 10 and May 30) in main plots and four diverse cotton cultivars [two Bt hybrids (NCS 855 BGII and RCH 650 BGII) and two non Bt genotypes (F 2228 and F 1861)] in sub plots of the split plot design with three replications. Results indicated that April sown crop acquired more growing degree days (2548-2664°C day), better heat use efficiency (1.09-1.15 kg ha^-1°C day^-1), and the pheno-thermal index (15.04-15.95°C) having significantly higher above ground biomass (7308-7985 kg ha^-1) as well as seed cotton yield (2887-3054 kg ha^-1) as compared to late sowing. Due to earlier completion of phenological duration, the Bt hybrids (NCS 855 BGII and RCH 650 BGII) exhibited superiority in thermal units conversion and economic yield over both non Bt cultivars. Thus, for effective utilization of the available thermal resources and to mitigate the adverse effects of harsh weather conditions on cotton productivity, the sowing of cotton should be done in April month in southwestern Punjab.