Nitrous Oxide Emissions with Enhanced Efficiency Nitrogen Fertilizers in a Rainfed System

The use of enhanced efficiency N fertilizers can increase crop N utilization and lead to lower emissions of the greenhouse gas N₂O. To determine the potential benefit of four enhanced efficiency fertilizers with rainfed corn (Zea mays L.) production in central Pennsylvania, N₂O emissions and grain yield were monitored during a 4-yr field study and compared with untreated urea prills and urea–NH₄NO₃ (UAN). The tested enhanced efficiency products were ESN (polymer-coated urea), SuperU (urease and nitrification inhibitor treated urea), UAN treated with AgrotainPlus (urease and nitrification inhibitors), and PiNT (cation-stabilized amine-N). Additionally, 28-d laboratory incubations were conducted to verify the potential differences in N cycling rates among N sources. The laboratory incubations indicated that ESN, SuperU, and treated UAN all had the potential to delay accumulation of NO₃ relative to untreated urea and UAN, but N cycling was similar with PiNT and the untreated fertilizers. Extended dry periods limited the denitrification potential and overall N₂O emissions in the field, but spikes of N₂O emission were seen within 1 mo after fertilizer application in each year. However, variation in emission rates was high within treatments, and no consistent differences among N sources were seen. Cumulative growing season N₂O emissions and grain yield were similar for all N sources in each year of the study. Enhanced efficiency fertilizers do not appear to be an effective means to reduce N₂O emission in a rainfed system, at least when rainfall is inconsistent.