Enhanced-efficiency fertilizer impacts on yield-scaled nitrous oxide emissions in maize

Balancing efforts to mitigate nitrous oxide (N ₂ O) emissions from crop production while increasing grain yields is an important challenge for agriculture. The objectives of this study were to assess N ₂ O emissions, soil inorganic nitrogen (N) concentrations, grain yield, and grain N content for three enhanced-efficiency nitrogen fertilizers (EENFs) compared with anhydrous ammonia in a rainfed corn system in Illinois over 3 yr (2015–2017). Treatments included a control (check) and four N sources applied at 202 kg N ha ^-1 : injected anhydrous ammonia, stabilized urea containing urease and nitrification inhibitors (SuperU, Agrotain International), polymer-coated urea (ESN, Agrium Advanced Technologies), and injected urea-ammonium nitrate (UAN) + nitrapyrin. Significant reductions in N ₂ O emissions were observed for several EENFs compared with anhydrous ammonia, but results were not consistent across treatments and years. SuperU reduced area- and yield-scaled N ₂ O emissions in two of three study years compared with anhydrous ammonia, while ESN had no N ₂ O mitigation benefit. Injected UAN + nitrapyrin had the highest emissions in the first year but significantly decreased emissions in the second 2 yr. No treatment significantly improved yield or grain N content compared with anhydrous ammonia. In light of efforts to broadly promote EENFs in the US Midwest, these results demonstrate there is some promise for N ₂ O mitigation, but the lack of clear crop productivity benefits combined with inconsistent N ₂ O mitigation effects do not support the conclusion that EENFs inherently improve agronomic and environmental outcomes.