Green manure returning improves wheat yield and N utilization efficiency by minimizing N loss in Oasis irrigation area of China

Improving crop yield and N utilization while mitigating environmental pollution is a key goal in sustainable agriculture. Integrating green manure with reduced chemical N application is a promising strategy to enhance N utilization efficiency and minimize reactive N losses. However, the agronomic mechanisms through which green manure incorporation affects soil N retention and N loss under reduced N application remain unclear. This study aimed to uncover the compensatory mechanisms of green manure in improving wheat yield and N utilization under reduced N application, and to identify the principles behind reduced N loss in wheat fields. We conducted a split-plot experiment in the Hexi Oasis irrigation area of Northwest China from 2019 to 2024, using two cropping systems (W, fallow after wheat; W-G, green manure returning after wheat) combined with three N application levels (N1, local conventional N application rate; N2, N-reduction 15%; N3, N-reduction 30%). Our results demonstrated that green manure returning improved soil quality and compensated for the yield and N use efficiency losses caused by 15% chemical N reduction. Specifically, compared to the W-N1, W-GN2 increased soil organic matter content and soil water content by 6.5% and 9.4%, respectively, while reducing soil bulk density and pH by 8.9% and 6.7%. Meanwhile, W-GN2 increased soil nitrate N and total N content in the 0–40 cm soil layer by 8.4% and 8.7%, respectively. Moreover, W-GN2 reduced NH₃ volatilization by 13.8%, N₂O emissions by 8.8%, and N leaching by 9.4%. It also enhanced microbial biomass N by 50.7%, urease activity by 10.2%, and decreased nitrate and nitrite reductase activities by 19.9% and 32.6%, respectively. Additionally, W-GN2 improved soil bacterial α-diversity and increased the abundance of functional bacteria. Green manure can sustain wheat yield and improve N utilization efficiency under reduced chemical N input by improving the soil environment, enhancing soil N retention and minimizing N losses, which presents a sustainable, yield-stabilizing strategy for Oasis agroecosystems in northwestern China.