Abstract:

Increasing nitrogen (N) utilization and reducing ecological costs of farmland are key objectives for mitigating environmental pollution and advancing sustainable agricultural development. Green manure is widely used to increase crop N efficiency while replacing partial chemical N input. However, it remains uncertain whether reducing chemical N supply, combined with mix-sowing green manures, could increase N utilization and reduce ecological costs of wheatland, revealing its mechanisms of soil N regulation and bacteria diversity. A 6-year field experiment was conducted in an arid irrigation area of northwestern China, implementing wheat multi-cropping different green manures and mix-sowing green manures (F, fallow; CV, common vetch; R, rapeseed; HCV, hairy vetch and common vetch) under reduced chemical N (N3, conventional N application rate; N2, reduced N by 20%; N1, reduced N by 40%). Our results showed that reducing chemical N decreased wheat yield and N efficiency, while green manure return increased wheat yield and N efficiency. Under N2, HCV had a higher wheat yield and N efficiency than CV, R, and F. Wheat N uptake and active N loss were decreased with chemical N reduction but enhanced with green manure return. HCVN2 improved wheat N uptake by 8.3% while reducing ammonia volatilization, nitrous oxide emissions, and nitrate leaching by 12.5%, 17.2%, and 22.1%, respectively, compared to FN3. The mechanisms of HCVN2 enhanced N utilization and reduced ecological costs of wheatland, mainly including increased N contents in the 0–40 cm soil layer, improved soil enzyme activities of N metabolism, and enriched soil bacterial diversity. Therefore, mix-sowing green manures return enhanced N utilization and decreased ecological costs of wheatland under a 20% reduction in chemical N input.