Evaluating Maize Yield under Deficit Irrigation Scenarios via the SSM Model

The Gorgan Plain, despite its location on the shores of the Caspian Sea, has arid and semi-arid climate, and the available water resources are insufficient to meet the demands of its vast agricultural fields. Therefore, irrigation management methods, such as deficit irrigation, must be employed to enhance productivity. However, it is essential to determine the optimal number of irrigations and the specific phenological periods during which the least reduction in yield and the highest productivity can be achieved. The aim of this study is to utilize the calibrated version of the SSM model over a 30-year period and apply statistical tests such as the Mann-Kendall, Pettitt, and Student’s t-tests to examine the trends in climatic parameters and assess and compare the average maize grain yields under deficit irrigation. To this end, maize was planted in (April 20th), the growth stages were divided into five phases, and irrigation was applied in 1 to 5 intervals during these phases. The results showed that the average rainfall in the region did not show significant changes, but there was a significant increase in both the daily minimum and maximum temperatures. These climatic changes led to a significant reduction in maize yield. Moreover, the sensitivity of the mid and late growth stages to deficit irrigation was higher than early stages. Severe deficit irrigation could cause a significant yield loss, but by increasing the number of irrigations from 1 to 4, the coefficient of variation in yearly yields decreased, and the best average yields were obtained with 2 to 4 irrigation intervals.