Nitrous oxide emissions with enhanced efficiency and conventional urea fertilizers in winter wheat

Reducing greenhouse gas emissions from agriculture is required to mitigate climate change. One strategy to do this from soils cropped with winter wheat may be modifying fertilizer type or application time. If these strategies better match N crop demand with fertilizer supply, excess soil N may be reduced, which may reduce nitrous oxide (N2O) emissions. Nitrous oxide is a potent greenhouse gas implicated in climate change. A three-year field trial tested whether enhanced efficiency fertilizers, which alter N availability from urea and different application times, influenced N2O emissions. We tested three different enhanced efficiency fertilizers (polymer-coated urea, urea with urease and nitrification inhibitor, and urea with nitrification inhibitor) that were split applied 30% banded at planting and 70% broadcast in late fall, or split applied 30% banded at planting and 70% broadcast at Feekes growth stage 4 (GS4, post-tiller formation, wheat entering the “greening up” phase in the early spring) compared to urea applied 100% at planting. Annual fertilizer rates ranged from 146 to 176 kg N ha-1. Over three years, cumulative N2O emissions ranged from 0.16 to 1.32 kg N ha-1. This was equivalent to between 0.009 and 0.688% of the nitrogen applied as fertilizer lost as N2O. We found that enhanced efficiency fertilizers did not lower N2O emissions, but emissions were lower when fertilizer was split applied at GS4 compared to in late fall. This suggests that rainfed winter wheat crops in Southern Alberta looking to minimize N2O emissions should consider a well-timed split application with a majority of fertilizer applied after winter rather than investing in enhanced efficiency fertilizers.