Spatially explicit estimates of N2 O emissions from croplands suggest climate mitigation opportunities from improved fertilizer management

With increasing nitrogen (N) application to croplands required to support growing food demand, mitigating N₂O emissions from agricultural soils is a global challenge. National greenhouse gas emissions accounting typically estimates N₂O emissions at the country scale by aggregating all crops, under the assumption that N₂O emissions are linearly related to N application. However, field studies and meta-analyses indicate a nonlinear relationship, in which N₂O emissions are relatively greater at higher N application rates. Here, we apply a super-linear emissions response model to crop-specific, spatially explicit synthetic N fertilizer and manure N inputs to provide subnational accounting of global N₂O emissions from croplands. We estimate 0.66 Tg of N₂O-N direct global emissions circa 2000, with 50% of emissions concentrated in 13% of harvested area. Compared to estimates from the IPCC Tier 1 linear model, our updated N₂O emissions range from 20% to 40% lower throughout sub-Saharan Africa and Eastern Europe, to >120% greater in some Western European countries. At low N application rates, the weak nonlinear response of N₂O emissions suggests that relatively large increases in N fertilizer application would generate relatively small increases in N₂O emissions. As aggregated fertilizer data generate underestimation bias in nonlinear models, high-resolution N application data are critical to support accurate N₂O emissions estimates.