Using pan evaporation method to estimate the maize evapotranspiration by dual crop coefficient approach

Prediction of crop evapotranspiration is important in irrigation scheduling and water resource management. The values of potential crop evapotranspiration are estimated by reference crop evapotranspiration (ETo) and crop coefficient. In this research, maize evapotranspiration (ETc) was measured by lysimeter in agricultural fields of Karkaj located in Tabriz University and was measured by water balance method in Bajgah Agricultural Experiment Station of Shiraz University. The values of ETc were estimated by considering ETo values and dual crop coefficient method. The values of ETo were estimated by using pan evaporation and Penman-Monteith methods. The measured seasonal values of ETc in agricultural fields of Karkaj and Bajgah in first and second year were 829, 814 and 818 mm, respectively. The estimated seasonal values of ETc by considering the estimated values of ETo by Penman-Monteith method in agricultural fields of the Karkaj and Bajgah in the first and second experimental years were 723, 693 and 700 mm, respectively. The estimated seasonal values of ETc by considering the estimated values of ETo from pan-evaporation method in agricultural fields of the Karkaj was 852 mm and in the Bajgah were 736 and 796 mm in first and second experimental years, respectively. The results confirmed that the calculation of ETo by considering pan-evaporation in dual crop coefficient method, improved the accuracy of crop evapotranspiration estimation.