Enhanced Efficiency Urea Sources and Placement Effects on N2O Emissions.

Nitrogen fertilizer management is important in determining soil nitrous oxide (N₂O) emissions. The effects of enhanced efficiency granular urea and placement on N₂O emissions from spring wheat at two locations in Manitoba, Canada in 2011 and 2012 were examined. Treatments were a control of no N addition and application of 80 kg N ha^-1 at planting with five combinations of urea sources and placement: broadcast-incorporated urea (Urea_I) and, subsurface side-banded urea (Urea_S), midrow-banded urea (Urea_M), midrow-banded ESN (ESN_M), and midrow-banded SuperU (SuperU_M). Planting in 2011 was delayed 40 days compared to 2012 because of late snow-melt. Planting coincided with higher soil temperature and moisture resulting in 3-7 fold more growing season N₂O emissions (∑N₂O) in 2011 than 2012 for all N treatments. In 2011, SuperU_M and ESN_M reduced ∑N₂O, emission factor scaled by N applied (EF), as well as yield-scaled N₂O emission intensity (EI) by 47%, 67% and 55%, respectively, compared with Urea_I. Although not significant, in 2011, banding treatments of urea tended to decrease ∑N₂O, EF, and EI of granular urea compared to broadcast-incorporation. The ∑N₂O and nitrate exposure, an integration of soil NO₃^- concentrations over time, were correlated with R² ranging from 0.46 to 0.67 over the site-years, indicating N availability from treatments in part determined emissions. Grain yield and crop N uptake did not vary with N sources and placement. These results suggest that for early season wet and warm conditions at application, EEF N sources can reduce emissions. The effect of banding in affecting emissions requires further investigations.