Optimizing the summer maize irrigation schedule in North Henan Province based on the DSSAT model

Henan Province is the main summer maize production area in China; however, the yield of maize in this region has been seriously threatened by water scarcity. It is important to improve maize yield and stability by appropriate irrigation allied to high water-use efficiency(WUE). In this study, we applied the Decision Support System for Agrotechnology Transfer(DSSAT) to determine the optimal irrigation schedules for summer maize in different hydrological years in the northern region of Henan Province. The GLUE procedure together with normalized root mean square errors(nRMSE), root mean square errors(RMSE), and index of agreement(d) showed that DSSAT-maize can be used to correctly predict maize yield, phenology, aboveground biomass, and soil water content. A calibrated model was used to simulate the effects of different irrigation treatments on the yield potential of summer maize in different hydrological years, and to evaluate the water shortages during the summer maize growing season. The optimal irrigation period was determined by comparing yield responses with different irrigation amounts and times, thereby enabling optimization of the irrigation schedule with yield and WUE. The results showed that water shortage in the summer maize growing season has varied significantly for the period of 1988-2017, averaging 38.91 mm, with a variation of 0 to 193.03 mm. In wet years, irrigation was unnecessary. Irrigation of 30 mm at the flowering stage should be applied in normal years and 50 mm at the flowering and grain-filling stages in dry years. In extraordinary dry years, irrigation of at least 180 mm should be applied at the emergence, jointing, and flowering stages of summer maize. Under the optimized irrigation schedule, when WUE reached the highest level in wet, normal, and dry years, the yield obtained accounted for 100%, 99.72%, and 97.89% of the maximum yield, respectively. The optimized irrigation schedule would produce a higher summer maize yield with the highest WUE.