Influence of rye cover cropping on denitrification potential and year-round field N 2 O emissions.

Cover cropping is beneficial for reducing soil erosion and nutrient losses, but there are conflicting reports on how cover cropping affects emissions of nitrous oxide (N ₂ O), a potent greenhouse gas. In this study, we measured N ₂ O fluxes over a full year in Illinois corn plots with and without rye cover crop. We compared these year-round measurements to N ₂ O emissions predicted by the Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation and the Denitrification-Decomposition (DNDC) model. In addition, we measured potential denitrification and N ₂ O production rates. The field measurements showed typical N ₂ O peaks shortly after fertilizer application, as well as a significant late-winter peak. Cover cropping significantly reduced all peak N ₂ O fluxes, with decreases ranging from 39 to 95%. Neither model was able to accurately predict annual N ₂ O fluxes or the decrease in N ₂ O emissions from cover-cropped fields. In contrast to field measurements, lab assays found that cover cropping significantly increased potential denitrification by 90-127% and potential N ₂ O production by 54-106%. The rye cover-cropped plots had lower soil nitrate and higher soil carbon. When limiting nitrate and excess carbon were provided in lab assays, the proportion of N ₂ O resulting from denitrification decreased. These results suggest that the discrepancy between the observed decrease in field N ₂ O emissions and the increase in denitrification potential may be due to the difference in available nutrients between the field and laboratory measurements. Overall, these results suggest the importance of late-winter peaks in N ₂ O emissions and the potential of rye cover cropping to reduce N ₂ O emissions from agricultural fields.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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