Including non-growing season emissions of N2O in US maize could raise net CO2e emissions by 31% annually

Nitrous oxide (N₂O) is a significant greenhouse gas and the most important currently emitted ozone depleting substance, primarily via agricultural fertilization. Current N₂O emission estimation methods at the national scale are predominantly via emission factors. Models estimating national-scale emissions are focused on growing season emissions. However, a substantial fraction of N₂O can be emitted during non-growing season periods. Using newly published off-season N₂O emission ratio maps and high-resolution nitrogen application data, this study explores the potential magnitude of underestimated N₂O emissions if using only the default growing-season focused methodology. Although there is large variation at county scales (12%–35%), non-growing season national emissions are estimated at 31% of the total, a potential 12,000 Gg CO₂e year⁻¹. Further work should better refine emission estimates spatially as well as fully integrate estimates across growing and non-growing seasons.