Optimal green manure application reduces nitrogen losses, enhances wheat grain yield, and improves nitrogen use efficiency

1. Incorporating green manure increases wheat grain yield and nitrogen use efficiency. 2. Increasing the amount of green manure incorporation decreases soil nitrate leaching risks. 3. Chemical N fertilizer combined with green manure reduced N 2 O emission, but increased NH 3 volatilization. Green manure application is an effective, eco-friendly method for improving crop yield and nitrogen use efficiency (NUE). However, the impact of varying green manure (GM) incorporation rates on nitrogen (N) loss, wheat grain yield, and NUE remains unclear. So, a long-term field experiment was conducted in an oasis region from 2020 to 2023. The experiment aimed to study the effects of different GM application rates on N loss in wheat fields and to elucidate the underlying mechanisms. The experiment tested two N levels (N0, 0 kg ha -1 ; N1, 180 kg ha -1 ) and four green manure application rates (G0, 0 kg ha -1 ; G1, 15,000 kg ha -1 ; G2, 30,000 kg ha -1 ; G3, 45,000 kg ha -1 ). The study evaluated the impact of synthetic N fertilizer combined with varying green manure levels on N losses, NUE, and wheat productivity. Relationships between N input, N losses, N use efficiency, and grain yield were also analyzed. Results showed that green manure application significantly increased soil nitrate-N storage (0-100 cm), reduced the risk of N leaching into deeper soil layers, lowered N 2 O emissions, and simultaneously boosted wheat grain yield (GY), although it also increased NH 3 emissions; however, NUE was improved. The N 2 O emissions from different amounts of green manure retention were decreased by 14.1 to 19.0%, compared to N1G0. Whereas in the N0, GM retention amendment increased the N 2 O flux by an average of 12.2%, compared to N0G0. The NH 3 emission in the N0 and N1 treatments was first enhanced then stabilized as the amount of green manure increased. The highest grain yield and N use efficiency were achieved with the N1G2 treatment. Simulations indicated that an optimal N input of 180 kg ha -1 synthetic N combined with 30,000 kg ha -1 green manure was required to maximize both wheat yield and NUE, while minimizing apparent N losses. Therefore, the green manure application strategy of N1G2 in this study could achieve higher wheat yield, improve NUE, reduce N losses, and mitigate soil nitrate leaching. This management strategy provides key insights for achieving high crop productivity with minimal N loss, offering a practical solution for sustainable agriculture.