Optimizing Irrigation Period and Amount of Superabsorbent in Soybean Using Response-surface Model

Soybean is considered as one of the valuable crops in terms of providing food, which has high amounts of protein and oil. This crop is sensitive to the amount of irrigation water. For this reason, it is suggested to determine the appropriate irrigation period along with the use of superabsorbent. To optimize these factors, the response-surface method was used in the present study. For this purpose, the soybean data collected from a research farm located in the Research Institute of Agricultural Engineering, in Iran, in 2018, was used. Two factors of irrigation period (with high and low levels of 4 and 7 days, respectively) and amount of superabsorbent (with high and low levels of 300 and 0 kg.ha-1, respectively) were applied. The results showed that the response surface method had an overestimation error (MBE>0) for predicting oil yield, and an underestimation error (MBE<0) for predicting other yield and yield components. The accuracy of this model for predicting all parameters were excellent (NRMSE<0.1) and its error was acceptable (RMSE<3%). The optimization results showed that seed yield, oil yield, protein yield, number of pods, plant height and water productivity were 169, 228, 227, 89, 34 and 131% higher than the average observed values of these parameters. In order to achieve optimal values, it is necessary to reduce the irrigation period to three days and use the amount of superabsorbent up to 50 kg.ha-1. Therefore, compliance with this issue is suggested for soybean cultivation.