Rational Water and Nitrogen Regulation Can Improve Yield and Water-Nitrogen Productivity of the Maize ( L.)-Soybean ( L. Merr.) Strip Intercropping System in the China Hexi Oasis Irrigation Area.

The planting area of the maize-soybean strip intercropping system has been increasing annually in the Hexi Corridor oasis irrigation area of China. However, long-term irrational water resource utilization and the excessive mono-application of fertilizers have led to significantly low water and nitrogen use efficiency in this cropping system. To explore the sustainable production model of high yield and high water-nitrogen productivity in maize-soybean strip intercropping, we established three irrigation levels (low: 60%, medium: 80%, and sufficient: 100% of reference crop evapotranspiration) and three nitrogen application levels (low: maize 230 kg ha, soybean 29 kg ha; medium: maize 340 kg ha, soybean 57 kg ha; and high: maize 450 kg ha, soybean 85 kg ha) for maize and soybean, respectively. Three irrigation levels without nitrogen application served as controls. The effects of different water-nitrogen combinations on multiple indicators of the maize-soybean strip intercropping system, including yield, water-nitrogen productivity, and quality, were analyzed. The results showed that the irrigation amount and nitrogen application rate significantly affected the kernel quality of maize. Specifically, the medium nitrogen and sufficient water (N2W3) combination achieved optimal performance in crude fat, starch, and bulk density. However, excessive irrigation and nitrogen application led to a reduction in the content of lysine and crude protein in maize, as well as crude fat and crude starch in soybean. Appropriate irrigation and nitrogen application significantly increased the yield in the maize-soybean strip intercropping system, in which the N2W3 treatment had the highest yield, with maize and soybean yields reaching 14007.02 and 2025.39 kg ha, respectively, which increased by 2.52% to 138.85% and 5.37% to 191.44% compared with the other treatments. Taking into account the growing environment of the oasis agricultural area in the Hexi Corridor and the effects of different water and nitrogen supplies on the yield, water-nitrogen productivity, and kernel quality of maize and soybeans in the strip intercropping system, the highest target yield can be achieved when the irrigation quotas for maize and soybeans are set at 100% ET0 (reference crop evapotranspiration), with nitrogen application rates of 354.78422.51 kg ha and 60.2771.81 kg ha, respectively. This provides guidance for enhancing yield and quality in maize-soybean strip intercropping in the oasis agricultural area of the Hexi Corridor, achieving the dual objectives of high yield and superior quality.