Supplementary irrigation and reduced nitrogen application improve the productivity, water and nitrogen use efficiency of maize-soybean intercropping system in the semi-humid drought-prone region of China

Maize-soybean intercropping systems are widespread in North China. However, the combined effects of supplementary irrigation and different nitrogen (N) application rates on the productivity, water use efficiency (WUE), and N use efficiency (NUE) of such systems remain unclear. A field experiment was conducted in a semi-humid drought-prone region in Northwest China in 2022 and 2023 to assess the interaction effects of supplemental irrigation and different N application rates on the crop yields, WUE, and NUE of a maize-soybean intercropping system and a monoculture system. Three cropping systems were used: maize-soybean intercropping, maize monoculture, and soybean monoculture, with two irrigation treatment scenarios (rainfed and supplementary irrigation at 30 mm) and three N fertilizer rates for maize (240, 180, and 120 kgN ha⁻¹). The land equivalent ratio (LER), $∆\text{water productivity}$ ($\text{WP}$), $∆\text{N harvest index}$ ($\text{NHI}$), and $∆\text{N partial factor productivity}$ ($\text{NPFP}$) of the maize-soybean intercropping system ranged from 1.06 to 1.11, 1.03–1.11, 1.17–1.34, and 1.16–1.28, respectively, demonstrating higher yields and resource of the intercropping system Supplementary irrigation significantly improved yield and resource use by improving the N complementarity effect and increased the economic by 17.24–31.16 %. A 25 % reduction in the N application rate (180 kgN ha⁻¹) for maize increased the NPFP without decreasing the crop yield and WP whereas, a 50 % reduction (120 kgN ha⁻¹) significantly decreased the crop yield and the economic benefits. In summary, supplementary irrigation can improve the productivity and resource use efficiency, and appropriate reduction of N fertilizer will not reduce the yield of intercropping system. This study provides practical insights for enhancing sustainable agriculture by improving water and N use efficiency in maize-soybean intercropping systems in the semi-humid arid-prone regions of China.