Nitrous oxide emissions from agricultural soils challenge climate sustainability in the US Corn Belt.

Agricultural landscapes are the largest source of anthropogenic nitrous oxide (N 2 O) emissions, but their specific sources and magnitudes remain contested. In the US Corn Belt, a globally important N 2 O source, in-field soil emissions were reportedly too small to account for N 2 O measured in the regional atmosphere, and disproportionately high N 2 O emissions from intermittent streams have been invoked to explain the discrepancy. We collected 3 y of high-frequency (4-h) measurements across a topographic gradient, including a very poorly drained (intermittently flooded) depression and adjacent upland soils. Mean annual N 2 O emissions from this corn-soybean rotation (7.8 kg of N 2 O-N ha -1 ⋅y -1 ) were similar to a previous regional top-down estimate, regardless of landscape position. Synthesizing other Corn Belt studies, we found mean emissions of 5.6 kg of N 2 O-N ha -1 ⋅y -1 from soils with similar drainage to our transect (moderately well-drained to very poorly drained), which collectively comprise 60% of corn-soybean-cultivated soils. In contrast, strictly well-drained soils averaged only 2.3 kg of N 2 O-N ha -1 ⋅y -1 Our results imply that in-field N 2 O emissions from soils with moderately to severely impaired drainage are similar to regional mean values and that N 2 O emissions from well-drained soils are not representative of the broader Corn Belt. On the basis of carbon dioxide equivalents, the warming effect of direct N 2 O emissions from our transect was twofold greater than optimistic soil carbon gains achievable from agricultural practice changes. Despite the recent focus on soil carbon sequestration, addressing N 2 O emissions from wet Corn Belt soils may have greater leverage in achieving climate sustainability.