Nitrous oxide is the largest greenhouse gas source from crop systems. DAYCENT was used to compare N₂O emissions from the following 3 bioenergy cropping systems: switchgrass, reed canarygrass, and a rotation of 3 yr corn, 1 yr soybeans, and 4 yr alfalfa. Although DAYCENT did not always capture the observed daily variability in N₂O emissions, it did simulate the observed seasonal patterns within systems and differences in mean emissions among systems reasonably well.