International initiatives such as the ‘4 per 1000’ are promoting enhanced carbon (C) sequestration in agricultural soils as a way to mitigate greenhouse gas emissions¹. However, changes in soil organic C turnover feed back into the nitrogen (N) cycle², meaning that variation in soil nitrous oxide (N₂O) emissions may offset or enhance C sequestration actions³. Here we use a biogeochemistry model on approximately 8,000 soil sampling locations in the European Union⁴ to quantify the net CO₂ equivalent (CO₂e) fluxes associated with representative C-mitigating agricultural practices. Practices based on integrated crop residue retention and lower soil disturbance are found to not increase N₂O emissions as long as C accumulation continues (until around 2040), thereafter leading to a moderate C sequestration offset mostly below 47% by 2100. The introduction of N-fixing cover crops allowed higher C accumulation over the initial 20 years, but this gain was progressively offset by higher N₂O emissions over time. By 2060, around half of the sites became a net source of greenhouse gases. We conclude that significant CO₂ mitigation can be achieved in the initial 20–30 years of any C management scheme, but after that N inputs should be controlled through appropriate management.

“千分之四”等国际举措正在促进增强农业土壤中的碳（C）固存，以减轻温室气体的排放¹。但是，土壤有机碳周转的变化会反馈到氮（N）循环^2中，这意味着土壤一氧化二氮（N ₂ O）排放量的变化可能会抵消或增强C的固存作用³。在这里，我们在欧盟^4的大约8,000个土壤采样位置上使用生物地球化学模型来量化净CO ₂当量（CO ₂e）与代表性的缓解C的农业实践有关的通量。只要保持碳积累（直到2040年左右），基于综合作物残渣保留和较低土壤扰动的实践都不会增加N ₂ O排放，此后到2100年导致适度的碳固存抵消，大部分低于47％。固氮覆盖作物在最初的20年中允许较高的C积累，但是随着时间的推移，N ₂ O排放量的增加逐渐抵消了这一增长。到2060年，约有一半的场地成为温室气体的净来源。我们得出结论，大量的CO ₂ 任何碳管理方案的最初20–30年都可以实现减排，但此后应通过适当的管理来控制N项投入。