Cover crops and in-season nitrogen (N) management are promoted as key conservation practices for reducing nitrate leaching losses from agricultural fields. However, their combined effects on soil nitrous oxide (N₂O) emissions per unit of crop productivity remains uncertain. These practices might contribute to high N₂O emissions by providing N and C substrates for microbial denitrification activity, especially when in-season N application coincides with cover crop decomposition. The objective of this study was to evaluate the effects of N application timing and cereal rye (CR, Secale cereale L) cover crops on area- and yield-scaled soil N₂O emissions in continuous maize (Zea mays L.) over 3-yr (2018–2020). Treatments were: Pre-Season-N: 224 kg N ha^-1 split-applied in fall + pre-plant in 2018, or as single pre-plant applications in 2019 and 2020; In-Season-N: pre-plant + side-dress (growth stage V6-V7); In-Season-N + CR: ; and a zero N plot as the Control. We found that shifting from pre-season to in-season split N application did not significantly affect area- or yield-scaled N₂O emissions in any year. Despite high N₂O spikes for the In-Season-N + CR following side-dress N application in all years, this did not translate to consistently higher cumulative N₂O emissions. Compared with Pre-Season-N and In-Season-N, In-Season-N + CR significantly increased area- and yield-scaled N₂O emissions by approximately 50% in 1 of 3 years. These results suggest the combination of high soil N supply, warm and wet soil conditions, and cover crop decomposition contributes to elevated N₂O emissions, but the cumulative effects of side-dress N application with a CR cover crop are variable across years. With increasing adoption of these practices to reduce nitrate leaching losses from croplands, future work should simultaneously assess effects on N₂O emissions and crop yield to account for potential tradeoffs in N loss pathways.

覆盖作物和当季氮 (N) 管理被推广为减少农田硝酸盐浸出损失的关键保护措施。然而，它们对每单位作物生产力土壤一氧化二氮 (N ₂ O) 排放的综合影响仍不确定。这些做法可能通过为微生物反硝化活动提供 N 和 C 底物而导致高 N ₂ O 排放，尤其是当季节性施氮与覆盖作物分解同时发生时。本研究的目的是评估氮肥定时和黑麦的谷物的影响（CR，黑麦 L）上面积-和产量缩放的土壤氮覆盖作物₂ O排放量在连续的玉米（玉蜀黍L.) 超过 3 年（2018-2020）。处理方法是： 季前-N：224 kg N ha ^-1在秋季 + 2018 年种植前分批施用，或在 2019 年和 2020 年作为单一的种植前施用；In-Season-N：种植前+侧装（生长阶段V6-V7）；季内 N + CR: ; 和零 N 图作为控制。我们发现，在任何一年中，从季前向季内施氮转变都不会显着影响面积或产量规模的 N ₂ O 排放。尽管在所有年份施氮肥后，季节性氮 + CR 的N ₂ O 峰值很高，但这并没有转化为持续较高的累积 N ₂ O 排放。与 Pre-Season-N 和 In-Season-N 相比，In-Season-N + CR 显着增加了面积和产量尺度的 N ₂O 排放量在 3 年中有 1 年减少约 50%。这些结果表明，高土壤氮供应、温暖和潮湿的土壤条件以及覆盖作物分解导致 N ₂ O 排放量增加，但侧施氮肥与 CR 覆盖作物的累积效应随年份变化。随着越来越多地采用这些做法来减少农田的硝酸盐浸出损失，未来的工作应该同时评估对 N ₂ O 排放和作物产量的影响，以考虑 N 损失途径中的潜在权衡。