Nitrous oxide emissions from agricultural soils challenge climate sustainability in the US Corn Belt
Agricultural landscapes are the largest source of anthropogenic nitrous oxide (N2O) emissions, but their specific sources and magnitudes remain contested. In the US Corn Belt, a globally important N2O source, in-field soil emissions were reportedly too small to account for N2O measured in the regional atmosphere, and disproportionately high N2O emissions from intermittent streams have been invoked to explain the discrepancy. We collected three years of high frequency (4-h) measurements across a topographic gradient including a very poorly drained (intermittently flooded) depression and adjacent upland soils. Mean annual N2O emissions from this corn–soybean rotation (7.8 kg N2O-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 N2O-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 N2O-N ha-1 y-1. Our results imply that in-field N2O emissions from soils with moderately to severely impaired drainage are similar to regional mean values, and that N2O 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 N2O emissions from our transect was two-fold greater than optimistic soil carbon gains achievable from agricultural practice changes. Despite the recent focus on soil carbon sequestration, addressing N2O emissions from wet Corn Belt soils may have greater leverage in achieving climate sustainability.
This is a manuscript of an article published as Lawrence, Nathaniel C., Carlos G. Tenesaca, Andy VanLoocke, and Steven J. Hall. "Nitrous oxide emissions from agricultural soils challenge climate sustainability in the US Corn Belt." Proceedings of the National Academy of Sciences 118, no. 46 (2021). doi:10.1073/pnas.2112108118. Posted with persmission.