denitrification enzyme assay treatments did not increase with added NO 3 , but did increase with added glucose. These results indicate that mineralizable C inputs can limit N 2 O emissions and that C inputs from the rye cover crop likely increased N 2 O emissions from fertilized soils. Mineralizable C availability should be considered in future evaluations of cover crop effects on N 2 O emissions, particularly as cover crops are evaluated as a potential strategy to mitigate agricultural N 2 O emissions.