Reference evapotranspiration (ETo) and crop water requirement (ETc) of wheat and maize in Gujarat
RASHMI MEHTAand VYAS PANDEY
The reference evapotranspiration (ETo) is an important agrometeorological parameter which has been used in a number of applications. In present study daily ETo was determined for 16 stations of Gujarat having long period (10-20 years) weather data following P-M approach. The Kc values for maize and wheat as given in FAO-56 was used in which Kcmid and Kcend were corrected for climatic conditions of stations. The corrected Kc values were used to calculate the daily crop water requirement (ETc) for wheat and rabi maize crops grown at different locations of Gujarat. The results revealed that during winter season (Nov. 15 to March 13) the mean daily (ETo) varies from 4.2 to 7.6 mm day-1. However the large variation in ETo across the locations (2.9 to 9.8 mm day-1) was observed, the lowest being at Khedbrahma and highest being at Targadia. The correction applied in Kcmid and Kcend suggested that at most of the stations Kcmid and Kcend for wheat crop were higher than that of FAO values while the corrected Kc values for maize were found to be less than that given by FAO. The mean water requirement (ETc) of wheat during its initial stage was found to be lower and almost constant and it increased continuously during developmental stage (from 1.9 to 5.2 mm day-1) and during the mid season stage (from 5.6 to 7.5 mm day-1) and decreased during the late-season stage (from 7.3 to 3.6 mm day-1). The seasonal water requirement across the locations varies between 400.5 mm (Khedbrahma) to 684.0 mm (Arnej). The mean water requirement of maize during initial stage is 1.3 mm day-1, during developmental stage 1.4 to 5.0 mm day-1, during the mid season stage ETc varies between 5.0 to 6.6 mm day-1 and during lateseason stage it decreases from 6.4 to 2.5 mm day-1 . The seasonal water requirement of rabi maize varies between 330.7 mm (Khedbrahma) to 520.5 mm (Bharuch).