Development of Improved Crop Coefficients for Precise Estimates of Wheat Evapotranspiration

Wheat is an important crop of India. Precise estimates of evapotranspiration can be obtained by multiplying crop coefficients to reference evapotranspiration using readily available climatic data. PenmanMonteith equation is adopted world wide as the most reliable and accurate method for computing reference evapotranspiration. The Food and Agriculture Organization (FAO) presented crop coefficients for estimation of evapotranspiration of different crops based on Penman-Monteith equation. The crop coefficient curves can be developed by plotting the ratios of crop evapotranspiration and reference evapotranspiration with respect to time. The crop coefficient curves developed by the FAO method are designated as FAO-56 curve method. The evapotranspiration values of wheat crop were measured with the help of electronic weighing lysimeter at Udaipur. The crop coefficient curves were developed for wheat by FAO-56 curve method and modified FAO56 curve method. The FAO-56 curve method underestimates wheat evapotranspiration by 28.17 per cent. Therefore, FAO-56 curve method does not appear to predict wheat evapotranspiration accurately. The modified FAO-56 curve method underestimates wheat evapotranspiration only by 5.55 per cent. Therefore, performance of modified FAO-56 curve method was found better than FAO-56 curve method for estimation of wheat evapotranspiration.