Determining optimal rates of nitrogen (N) fertilization in corn-soybean systems is necessary to maximize production while protecting air and water quality. The production of greenhouse gases, particularly nitrous oxide (N₂O), is a major environmental impact of corn-soybean production that has been shown to vary with N fertilization rates and cover cropping practices. However, previous studies have not found consistent relationships between these practices and N₂O emissions. There is a need to clarify how basic carbon (C) and N cycling processes affect the relationships between fertilizer rate, cover cropping, and N₂O emissions. We compared soil N₂O and carbon dioxide (CO₂) emissions and soil N cycling processes between a wide range of N application rates (0 to 224 kg/ha) with and without a winter rye cover crop in a no-till 2-yr corn-soybean rotation. Preliminary results show no differences in cumulative N₂O fluxes between N fertilization rates of 135 and 224 kg N/ha, and no significant effect of cover cropping on N₂O emissions. The results of this study contribute to quantifying the global warming impact of Midwestern corn-soybean agriculture.