Nitrogen Reduction Combined With Organic Fertilizer: Key Practices to Enhance Soil Quality and Crop Productivity While Mitigating <scp> N ₂ O </scp> Emissions

ABSTRACT Partial substitution of chemical fertilizers with organic alternatives can reduce reliance on synthetic nitrogen (N) fertilizers, yet its comprehensive effects on soil quality, productivity, and environmental sustainability remain unclear. A winter wheat–summer maize rotation experiment was conducted to investigate variations in soil properties, crop productivity, N uptake, N 2 O emission, and N cycle functional genes under sufficient N (NF), N reduction (RN), N reduction combined with low (RNM1) and high (RNM2) amounts of organic fertilizer treatment. Compared with RN, NF, RNM1, and RNM2 markedly improved soil quality index (SQI) (59.29%–243.19%), productivity (5.06%–79.42%), crop N uptake (5.05%–32.04%), and N 2 O emissions (2.29%–109.45%). These benefits were primarily driven by increases in soil organic carbon, available phosphorus and N, dissolved organic carbon, and microbial biomass carbon and N, which enhanced SQI and promoted crop performance. RNM1 and RNM2 markedly reduced annual N 2 O emissions by 17.98%–51.16% and 13.69%–23.93%, respectively, compared with NF. This mitigation was associated with lower soil available N, reduced abundances of nitrification and denitrification genes ( amoA , amoB , amoC , narG , narH , norB ), and higher nosZ abundance, which promotes N 2 O reduction to N 2 . Synthesizing current and prior results suggests that reducing synthetic N by less than 45% while applying organic fertilizer can maintain productivity without increasing emissions. Among all treatments, RNM1 emerged as the most balanced strategy, simultaneously enhancing N uptake, soil quality, and yield while mitigating N 2 O emissions. Although yield gains under organic fertilizer treatment were comparable to NF, the additional environmental benefits highlight the need for further research to optimize organic–inorganic fertilizer ratios and application rates to maximize agronomic and ecological outcomes.