Global cropland nitrous oxide emissions in fallow period are comparable to growing‐season emissions

Abstract Croplands account for ~ one‐third of global anthropogenic nitrous oxide (N 2 O) emissions. A number of recent field experiments found substantial fallow‐period N 2 O emissions, which have been neglected for decades. However, the global contribution of the fallow‐period emissions and the associated drivers remain unclear. Based on 360 observations across global agroecosystems, we simulated the ratio of the fallow to the whole‐year N 2 O emissions (R fallow ) by developing a mixed‐effect model and compiling cropping‐system‐specific input data. Our results revealed that the mean global gridded R fallow was 44% (15%–75%, 95% confidence interval), with hotspots mainly in the northern high latitudes. For most cropping systems, soil pH was the dominant driver of global variation in R fallow . Global cropland emission factors (i.e., the percentage of fertilizer N emitted as N 2 O, EFs) in EF‐based models doubled to 1.9% when the fallow‐period N 2 O emissions were included in our simulation, similar to EFs estimated by process‐based and atmospheric inversion models (1.8%–2.3%). Overall, our study highlights the importance of fallow‐period N 2 O emissions in annual totals, especially for single cropping systems and croplands in acidic areas. To accurately estimate N 2 O emissions for national greenhouse gas inventories, it is crucial to update current EFs with full consideration of the fallow‐period N 2 O emissions in the Intergovernmental Panel on Climate Change (IPCC) Tier 1 method.