Estimation of Stress Coefficients, Plant Coefficients and Yield Response to Water in Peanut under Different Levels Irrigation

To estimate stress coefficients (Ks), plant coefficients (Kc) and plant sensitivity coefficients (Ky) to water at different stages of peanut growth, a study in the form of split plots in a randomized complete block design in three repetitions was performed in 2017 and 2018 in Guilan province. The main treatments included rainfed, and supply of 120, 100, 80, 60, and 40% of water requirement and the sub-treatments were two peanut cultivars of Jonobi and Guil. According to the results, the values of water stress coefficients in the Jonobi cultivar varied from 0.45 to 0.63 in 2017 and 2018, respectively. This coefficient, however, was in the range of 0.47-1 in 2017 and 0.64-1 in 2018 for the cultivar Guil. Plant coefficient in the initial stage (20 days), plant development (30 days), middle (45 days) and final (30 days) was 0.4, 0.37, 1.01, and 0.79 during 2017, and 0.4, 0.37, 0.98, and 0.75 in 2018 for Jonobi cultivar, respectively. These coefficients were 0.4, 0.36, 1.01 and 0.78 in 2017, and 0.4, 0.36, 0.98 and 0.74 in 2018 for Guil cultivar, respectively. Calibration of sensitivity coefficient in Guil and Jonobi cultivars was studied by Raes (2004) and Tafteh et al. (2013) methods, and it was found that in Raes (2004) method, the root mean square error of 183 kg.ha-1 and its normalized value was about 16% and the efficiency index of this method was 0.72. In Tafteh et al. (2013) method, the mean root mean square error was 188 kg.ha-1 and its normalized value was about 17% and the efficiency index of this method was 0.71. Overall, Raes (2004) with NRMSE of 0.164 and Tafteh et al. (2013) with an NRMSE of 0.168, showed an acceptable accuracy in estimating peanut yield.