Optimization of furrow irrigation programs of summer maize by using the AquaCrop model and WinSRFR software

Determining a reasonable irrigation schedule for crops and a combination of irrigation technology elements is the basis for scientific management of agricultural water resources, which can effectively alleviate the contradiction of water scarcity and guarantee regional food security. In this study, the AquaCrop model was calibrated and validated based on the summer maize field experiments in Yangling (2022) and Wugong (2017), Shaanxi Province to optimize the irrigation schedule, and the irrigation schedule of summer maize under typical hydrological years (wet year, normal year and dry year) and the required irrigation depth were determined in the study area; the WinSRFR software was calibrated and validated using the Yangling (2022) irrigation experiment; and the soil infiltration parameters of F4, F7, and F5 were selected to be representative of high (k = 98.437 mm/h^α, α = 0.824), moderate (k = 85.396 mm/h^α, α = 0.659), and low (k = 55.416 mm/h^α, α = 0.617) infiltration capacities, and 1.0‰, 2.0‰ and 3.5‰ were used as representative values of typical bottom slopes in the study area, respectively to optimize values furrow irrigation technology elements (discharge and cutoff time) under different soil infiltration capacities and bottom slope by using WinSRFR. Finally, evaluation the yield increasing ability of the optimized irrigation schedule and the irrigation technology elements for summer maize by using AquaCrop model, respectively. The results indicated that the AquaCrop model can accurately simulated the maize growth. The calibration results of the coefficient of determination (R²), root mean square error (RMSE) and Nash-Sutcliffe efficiency coefficient (EF) between simulated and measured values of canopy cover (CC), aboveground biomass (B) and soil water content (SWC) were 0.99, 0.98, 0.89; 3.9%, 1.4 t/hm², 11.7 mm; and 0.97, 0.94, 0.56, respectively; the verification results were 0.98, 0.99, 0.86; 10.1%, 1.2 t/hm², 13.6 mm, and 0.76, 0.96, 0.63, respectively; The calibration and verification results of the mean absolute value of the relative error between the simulated and measured values of yield was 1.85% and 7.47%, respectively; Summer maize in the study area must be irrigated once during wet year (during the grain-filling stage) and normal year (during the jointing stage) and twice during dry year (during the jointing and grain-filling stages), with the water quantity used in each irrigation event being 55 mm; the optimised k and α values were 55.416 to 98.437 mm/h^α and 0.35 to 0.858, respectively, and the mean n value was 0.056; the optimal discharge and cutoff times were 2.2 to 3.3 L/s and 35 to 16 min, respectively, these values are suitable for meeting the requirement of the comprehensive irrigation performance indicator (C_i) being ≥ 85%. Based on the irrigation schedules of optimization and the combination of irrigation technology elements of optimization for summer maize in 2022, the yield of maize simulated by AquaCrop model is 7.819 t/hm²; compared with rain fed (5.972 t/hm²), current condition (7.424 t/hm²) and irrigation schedule of optimization (7.659 t/hm²), summer maize yield increased by 1.847, 0.395 and 0.160 t/hm², respectively; and the percentage of summer maize yield increase by 30.9%, 5.3% and 2.1%, respectively, and saved irrigation water 59 mm. Therefore, the optimization of irrigation system and irrigation factor combination can effectively improve crop yield and save irrigation water; and it can be concluded that although irrigation is only used as a supplement to crop water requirements in semiarid and semi-humid, it is important because it has substantive implications on maize yield. The research results can provide theoretical basis for furrow irrigation scheme design of the research region and technology support.