Maize production and nitrous oxide emissions from enhanced efficiency nitrogen fertilizers

Enhanced efficiency nitrogen fertilisers (EENFs) attempt to improve nitrogen use efficiency (NUE) by synchronizing nitrogen (N) supply with crop demand to improve crop productivity/profitability and minimize environmental impacts. This study evaluated the impact of ten EENFs (at 125 and 250 kg N ha−1) compared to urea-N (at 0, 62.5, 125, 175, 250 and 300 kg N ha−1) subsurface banded in a no-till maize (Zea mays L.) production system. Crop growth was examined in both the year of application and in the following year (without fertiliser N) to assess residual impacts. Nitrous oxide emissions from a subset of EENFs applied at 150 kg N ha−1 in an adjacent experiment were monitored in year 1. Grain yield increased with increasing rates of applied urea-N in year 1, with a maximum potential yield of 11.2 t ha−1 achieved at ≥ 175 kg N ha−1. However, grain and biomass yield, agronomic NUE, and N transfer efficiency did not increase with EENFs compared to urea-N, and some controlled release fertilisers (CRFs) decreased yield by 9–16%. Nitrification inhibitors decreased cumulative N2O emissions by 67%, while CRFs had no significant effect. Residual fertiliser N remaining in the soil at the end of the first season was strongly correlated with grain yield in the subsequent cropping year, but EENFs did not have a greater residual impact on crop growth than urea-N. The inability of EENFs to deliver increased crop N uptake or grain yield does not provide a clear case for their use as an alternative to conventional urea.