Crop straw incorporation interacts with N fertilizer on N2O emissions in an intensively cropped farmland

Nitrogen (N) fertilization and straw incorporation strongly influence nitrous oxide (N2O) emissions from agricultural fields. An in-situ micro-plot experiment on intensively farmed winter wheat (Triticum aestivum L.) was conducted to investigate the source and rate of N2O emissions from soils following labeled 15N fertilization with and without straw incorporation. Four treatments, i.e., no N fertilizer and no straw incorporation (N0S0), straw incorporation only (N0S1), N fertilizer only (N1S0), and N fertilization plus straw incorporation (N1S1), were established in the experiment. The N2O emissions mainly occurred after N fertilization and lasted for approximately 1–2 weeks, accounting for 60%–67% of the wheat seasonal N2O emissions. Within the 6 days after basal fertilization and 2–4 days after top-dressing, most of the N2O fluxes (>50%) were derived from fertilizer. Thereafter, soil-derived N2O dominated the total N2O emissions and within 10–20 days after N fertilization, fertilizer-derived N2O became negligible. Fertilizer N and soil N both accounted for 40%–60% of the seasonal N2O emissions, which may be explained by the high soil N stock due to long-term high N fertilization in the region. This implies the similar roles of soil N pool and fertilizer N in N2O generation under intensively farmed soils. The N fertilization had a significant priming effect on the turnover of soil N, which contributed 21.02%–50.47% of the total N2O emissions. During the basal fertilization/first irrigation event, straw incorporation significantly (P < 0.05) stimulated CO2 fluxes both in N-fertilized and non-N-fertilized plots; however, after the top-dressing/second irrigation event, the significant increase of CO2 fluxes induced by straw incorporation was only observed in the N-fertilized treatment. Straw incorporation interacted with N fertilization, and tended to enhance N2O emissions in the basal fertilization and lower N2O emissions in the top-dressing period. In N-fertilized plots, the seasonal N2O emissions from straw-incorporated and straw-removed treatments were similar, indicating that straw incorporation enhanced the N supply without increasing the N2O emissions. Our study highlights that there are significant benefits of straw incorporation to soil fertility improvement; however, the long-term impacts of straw incorporation on greenhouse gas emissions should be further examined.