Influence of rye cover cropping on denitrification potential and year-round field N₂O 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 (N₂O), a potent greenhouse gas. In this study, we measured N₂O fluxes over a full year in Illinois corn plots with and without rye cover crop. We compared these year-round measurements to N₂O 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 N₂O production rates. The field measurements showed typical N₂O peaks shortly after fertilizer application, as well as a significant late-winter peak. Cover cropping significantly reduced all peak N₂O fluxes, with decreases ranging from 39 to 95%. Neither model was able to accurately predict annual N₂O fluxes or the decrease in N₂O 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 N₂O 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 N₂O resulting from denitrification decreased. These results suggest that the discrepancy between the observed decrease in field N₂O 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 N₂O emissions and the potential of rye cover cropping to reduce N₂O emissions from agricultural fields.