Nitrous oxide emissions under different corn field managements in the United States

Nitrous oxide (N2O) is a potent greenhouse gas that also contributes to stratospheric ozone depletion. Intensive nitrogen fertilizer use has increased agricultural N2O emissions and motivated research efforts to identify field management techniques that best mitigate N2O emissions and reduce these negative environmental impacts. In this study, field N2O emissions were quantified during the 2016 growing season by direct field measurement from corn fields in Champaign, Illinois. Measurements were used to compare N2O emissions between plots differing in fertilizer rate, cover cropping, and tillage. In addition, corn fields in Illinois, Minnesota, and Colorado were modeled using the process-based Denitrification Decomposition (DNDC) model, which is used to predict trace gas emissions from agriculture based on field and climate conditions. The DNDC model was evaluated for predicting N2O emissions from corn cropping systems in the United States by comparing published field measured emissions to model predictions. Field N2O emissions from the Illinois site were generally low (0-211 gN/ha/d), making observed differences between treatments difficult to discern. While fertilized plots had up to 93% higher N2O emissions than unfertilized plots on some days, the difference was not significant in most cases (P>0.05). Cover cropping and tillage treatments did not significantly affect N2O emissions. Model results from DNDC did not consistently predict magnitudes and trends of N2O emissions at the daily scale, especially during years of heavy rainfall after drought. DNDC predictions consistently included high N2O emission peaks before fertilization in late winter to early spring. However, such peaks were not observed in the Colorado field measurement study, the only one that included year-round weekly measurements. Cumulative growing season modeled and measured N2O emissions were of similar magnitude, although their difference was statistically significant for the Colorado site (P=0.0009). DNDC results accurately reflected cumulative emission trends associated with varying fertilizer rate, but not those from tillage differences, likely because the influence of tillage on N2O emissions is not well parameterized in the model due to lack of consensus on tillage effect. Model calibration did not improve N2O emission predictions beyond the year and treatment it was calibrated for. DNDC is useful for predicting cumulative growing season N2O emission trends associated with fertilizer application, but needs further modification to improve daily scale predictions and trends associated with other managements