Abstract

R B Singandhupe *, A Manikandan, D Blaise and S Chattaraj

Moisture stress at the critical stage is a major constraint in rainfed cotton. Assessment of reference evapotranspiration (ETo) and its utilization strategy is imperative to boost rainfed cotton production. To overcome, daily meteorological parameters of 10 cotton growing districts of Gujarat, India were recorded from 2001 to 2011 and multiple regressions between lint yields and various climatic variables, crop evapotranspiration (ETc) at four critical stages of cotton were done. Water deficit, surplus, actual evapotranspiration, soil storage, change in soil water storage was calculated for different non-Bt. and Bt. cotton-growing years. The results revealed that ETo was 662-947, 414-687, and 1076-1596 mm, and rainfall was 490-1150, 5.5-35, and 442-1210 mm from June to December, January-April and overall crop growth period, respectively. The impact of rainfall, ETc on lint yield was 51 to 92 % (R2) and was highly significant at the critical growth stage. The ETc was 670 to 936 mm and the water use efficiency (WUE) was 0.13 to 0.83 kg /hamm. Low WUE was recorded in non-Bt growing years. Based on the meteorological parameters, it is concluded that under rainfed situation the supplemental irrigation is essential after the withdrawal of monsoon rain and in extended cotton (January-April). The conserved rainwater could be effectively used during the cotton boll development stage, which intern increases the lint yield as well as WUE.