Comparison of calculation methods for determining evapotranspiration under drip irrigation

The accuracy of calculation methods for determining the evapotranspiration (ET) of corn for grain under drip irrigation in the steppe of Ukraine was established. A comprehensive assessment of calculation methods for soil optimal water regime formation during different growth phases of maize plants was carried out. The accuracy of the estimated value of evapotranspiration was determined by the mean absolute percentage error (MAPE). It has been proven that the use of calculation methods without taking into account the climatic conditions of Southern Ukraine leads to a significant error in determining the actual evapotranspiration. By the Penman-Monteith method, the MAPE of 16.3-26.9% corresponds to the good and satisfactory accuracy of the chosen calculation model. Using the methods of A.M. and S.M. Alpatyev as well as D.A. Stoyko the MAPE increased to 22.2-39.7% and 20.8-29.1%, respectively, which proved their satisfactory accuracy. The calculation method of M.M. Ivanov ensured the MAPE of 48,7-76,8%; that is unsatisfactory calculation accuracy. Adapted crop coefficients Kc for the conditions of the South of Ukraine increased the accuracy of calculating ET by the Penman-Monteith method by an average of 2,2 times, D.A. Shtoyko and A.M. and S.M. Alpatiev by 1,9 and 2,2 times, and M.M. Ivanov by 4,4 times. An analysis of the MAPE using various calculation methods for determining the evapotranspiration of corn for grain under drip irrigation showed that the Penman-Monteith method provides the smallest error (MAPE = 9.1%), which corresponds to high prediction accuracy. In a wet year, the accuracy of ET determination decreases by all methods, which indicates an increase in the MAPE: by Penman-Monteith and D.A. Shtoyko - up to 11.9% and 18.7%, respectively, and the determination accuracy decreases to category “good”. When calculating using the methods of A.M. and S.M. Alpatiev and M.M. Ivanov the MAPE increased to 23,3% and 21,5%, respectively, and the accuracy of ET determination was satisfactory.