The effects of split application of enhanced efficiency fertilizers on non-winter nitrous oxide emissions from winter wheat

This study tested if non-winter cumulative nitrous oxide (N2O) emissions, emission factors, and yield-scaled N2O emissions were affected by split application of enhanced efficiency nitrogen fertilizers in a rainfed winter wheat crop. Based on initial soil tests, fertilizers were applied at 84 kg N ha(-1) in year 1 and 72 kg N ha(-1) in year 2. Two trials were completed each year. Trial 1 applied (1) urea, (2) urea with nitrification inhibitor, (3) nitrification and urease inhibitors, and (4) polymer-coated urea as (1) 100% side-banded at planting, 30% side-banded at planting and (2) 70% surface-applied in late fall, or (3) 70% surface-applied in spring at Feekes growth stage 4 (GS4). Trial 2 applied (1) urea-ammonium nitrate (UAN), (2) UAN treated with nitrification inhibitor, (3) urease inhibitor, (4) a combination of both, (5) granular urea, and (6) polymer-coated urea, all applied 50% side-banded at planting and 50% surface-applied at GS4. Cumulative N2O emissions from fertilized soils ranged from 0.101 to 0.433 kg N ha(-1). The emission factors for trial 1 were greater in year 1 than year 2 (P <= 0.05). There were no treatment differences in cumulative N2O emissions in trial 2. However, cumulative N2O emissions, emission factors, and yield-scaled N2O emissions from trial 1 were higher when fertilizer was split-applied in late fall compared with at GS4 (all P <= 0.05). This study demonstrates that under best management practices, it is better to apply the required rate in the form of conventional fertilizer at planting rather than split application.