Mitigation potential of soil carbon management overestimated by neglecting N2O emissions

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) cycle(2), meaning that variation in soil nitrous oxide (N2O) emissions may offset or enhance C sequestration actions(3). Here we use a biogeochemistry model on approximately 8,000 soil sampling locations in the European Union(4) to quantify the net CO2 equivalent (CO(2)e) 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.