Effect of Variability in Climate and Irrigation Regimes on Evapo-transpiration and Water Use in Spring Maize

A simple soil water balance approach was used to estimate actual evapotranspiration of spring maize under variable irrigation regimes for two years on loamy sand soil in a semi arid, subtropical region of north India. Moisture stress to crop was created through three irrigation regimes (irrigation water/open pan evaporation ratio of 1.2 (I_1.2), 0.9 (I_0.9) I_0.9 and 0.6 (I_0.6)). Depending upon the changes in climate, year 2007 was hot and dry (9.5 cm less rainfall) compared to 2008. During dry season cumulative actual evapotranspiration was greater than the potential evapotranspiration by 14.4 and 6.6 per cent under I_1.2 and I_0.9 irrigation regimes, respectively. However under I_0.6 cumulative actual evapotranspiration was lower than potential evapotranspiration by 3.6 per cent. In wet season cumulative actual evapotranspiration was increased by 14.9, 10.8 and 4.7 per cent under I_1.2, I_0.9 and I_0.6 irrigation regimes, respectively over potential evapotranspiration. During wet season irrigation regime I_0.9 was at par with I_1.2 in water use efficiency (WUE) thus, more helpful in saving irrigation water. However during dry season irrigation regime I_1.2 was beneficial for increasing WUE through increased grain yield. Rainfall favoured the crop growth and grain yield through lowering air temperature and reducing evaporation and recharging soil water storage. Crop coefficients were increased exponentially with leaf area index (LAI) in all treatments and the variability in crop coefficient was more during dry season compared to wet season.