Maize/soybean intercropping with nitrogen reduction: A pathway for improved nitrogen efficiency and reduced environmental impact in Northwest China

Soybean intercropping holds promise for improving maize productivity and nitrogen use efficiency; however, comprehensive studies on the impacts of reduced nitrogen topdressing on system productivity, nitrogen dynamics, and environmental outcomes are still limited. In this study, field experiments were conducted from 2023 to 2024 in Northwest China, comparing traditional maize and soybean monoculture with maize/soybean intercropping that included reduced nitrogen topdressing at 25 %, 50 %, 75 %, and 100 % of the conventional rate (240 kg ha^–1) for maize. The study revealed that while maize/soybean intercropping reduced crops yield due to decreased planting density, it significantly improved maize nitrogen status (nitrogen nutrient index closer to 1) compared to traditional monoculture. Although soybean nitrogen fixation and accumulation were inhibited, the intercropping maintained a yield advantage (land equivalent ratio > 1). Notably, intercropping reduced soil nitrate nitrogen residue by approximately 10 % and NH₃ volatilization by over 20 % compared to maize monoculture. The intercropping improved nitrogen balance and environmental sustainability, enhancing maize nitrogen partial factor productivity by 26.76 % (2023) and 23.63 % (2024). Furthermore, reducing nitrogen topdressing effectively minimized nitrogen residue and ammonia volatilization without compromising intercropping yield or nitrogen efficiency, despite partial inhibition of soybean nitrogen fixation. These findings suggest that maize/soybean intercropping combined with moderate reduction of nitrogen topdressing can support more sustainable nutrient management practices in Northwest China.