Research on Summer Maize Irrigation and Fertilization Strategy in Henan Province Based on Multi-Objective Optimization Model

Identifying a water–nitrogen coupling strategy to achieve high efficiency, emission reduction, and optimal yield in summer maize under multi-objective conditions is crucial for enhancing nitrogen fertilizer utilization and promoting agricultural sustainability. This study conducted a field experiment on water–fertilizer coupling in summer maize, with three irrigation levels (60%θf, 70%θf, 80%θf, with θf representing field capacity) and four nitrogen application levels (0, 180, 270, 360 kg/ha). It analyzed variations in yield, partial factor productivity of nitrogen fertilizer (PFPN), and the soil CO2 emission flux across different water–nitrogen combinations, establishing a multi-vector optimization model. NSGA-III (non-dominated Sorting Genetic Algorithm III) was utilized to determine the most effective combination of water and nitrogen. The results indicated that maize yield initially increases and then declines as irrigation and nitrogen levels rise. PFPN showed a decreasing trend, and its decline gradually decreased with increasing irrigation levels, suggesting that water can alleviate nitrogen stress to some extent. Soil carbon dioxide exhalation intensity increased with both irrigation and nitrogen levels. The NSGA-III optimization revealed that the optimal water–nitrogen ratio is 1086.28 m3/ha for irrigation and 265.79 kg/ha for nitrogen. Compared with the best water–nitrogen combination (W2N3) from the experiment, this optimized scheme showed no significant difference in irrigation volume, yield, or soil CO2 emission flux while increasing PFPN by 13.46% and saving 1.56% of nitrogen fertilizer. In summary, the optimized water–fertilizer coupling scheme provides a scientific basis for high-efficiency, high-yield, and low-emission maize production in Henan Province, supporting sustainable agricultural development.