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

Nitrous oxide (N 2 O) is a significant greenhouse gas and the most important currently emitted ozone depleting substance, primarily via agricultural fertilization. Current N 2 O 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 N 2 O can be emitted during non‐growing season periods. Using newly published off‐season N 2 O emission ratio maps and high‐resolution nitrogen application data, this study explores the potential magnitude of underestimated N 2 O 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 CO 2 e year −1 . Further work should better refine emission estimates spatially as well as fully integrate estimates across growing and non‐growing seasons.