Crop straw incorporation alleviates overall fertilizer-N losses and mitigates N2O emissions per unit applied N from intensively farmed soils: An in situ 15N tracing study.

A thorough elucidation of the coupled effects of N fertilization and straw incorporation on N2O emissions and N losses is crucial for alleviating negative environmental impacts in intensively farmed regions. Here, we conducted an in situ 15N tracing experiment to assess the source of N2O emissions and fate of fertilizer-N in soil intensively farmed with summer maize (Zea mays L.). Four treatments, i.e., no N fertilization and no straw incorporation (N0S0), straw incorporation only (N0S1), N fertilization only (N1S0), and N fertilization plus straw incorporation (N1S1), were established in the study. Compared with straw removal, straw incorporation increased the seasonal N2O emissions by 22.3% but reduced the N2O emissions per unit of applied N by 6.22% (P > 0.05). The emission of fertilizer-derived N2O occurred mainly in the 13-17 days after fertilization; thereafter, the ratio of fertilizer-derived N2O fluxes would be less than 5%. N fertilization significantly stimulated non-fertilizer-derived N2O emissions and soil CO2 fluxes, especially when straw was incorporated (P < 0.05), indicating that N fertilization might have triggered the mineralization of straw-N and/or native soil organic N. The soil NO3--N concentration in straw-incorporated plots tended to be lower than that in straw-removed plots, especially after N fertilization events. Straw incorporation sequestered 52.5% (27.4 kg N ha-1) more fertilizer-N in 1 m of soil than straw removal (P < 0.05) while significantly increasing the fertilizer-N harvest index and maintaining grain yield. Overall, compared with straw removal, straw incorporation significantly reduced total fertilizer-N losses (by 12.8%, i.e., 14.58 kg N ha-1; P < 0.05). Our study highlights the benefits of straw incorporation for increasing in-season and multiseason fertilizer-N use efficiencies and alleviating fertilizer-N-induced environmental costs in intensively farmed regions.