Enhanced Efficiency Urea Sources and Placement Effects on Nitrous Oxide Emissions.

The effects of band placement of enhanced efficiency fertilizers (EEF) on nitrous oxide (N₂O) emissions are uncertain. Placement and EEF on N₂O emissions from spring wheat (Triticum aestivum L.) at two locations in Manitoba, in 2011 and 2012 were examined. Treatments were a no N control and 80 kg N ha^-1 at planting of five combinations of placement and granular N source: broadcast-incorporated urea (Ureaj) and, subsurface side-banded urea (Urea _M; each row side-banded), midrow-banded urea (Urea_M; placement between every other set of rows), midrow-banded environmentally smart nitrogen (ESN, Agrium, Inc.) (ESN_M), and midrow-banded SuperU (Koch Industries Inc.) (SuperU_M). Planting in 2011 was delayed 40 d compared to 2012. Planting coincided with higher soil temperature and moisture resulting in three- to sevenfold more growing season N₂O emissions (ΣN₂O) in 2011 than 2012. In 2011, SuperU_M and ESN_M reduced ΣN₂O, emission factor (EF) scaled by N-applied EF, and yield-scaled N₂O emission intensity (El) by 47, 67, and 55%, respectively, compared with Ureaj. In 2011, increasing placement concentration of N in order broadcast-incorporation, side-banding, and midrow-banding tended to decrease ΣN₂O, EF, and El of granular urea, but not statistically significant. The ΣN₂O and nitrate exposure (NE), were significantly correlated over the site-years, indicating N availability from treatments in part determined emissions. Grain yield and crop N uptake were unaffected by sources and placement. These results suggest for early season wet and warm conditions, EEF N sources can reduce emissions compared with granular urea. Further studies are required to clarify placement effects on N₂O emissions. [ABSTRACT FROM AUTHOR]