Mineral nitrogen source controls N₂O emissions and emission factors in drip-irrigated semiarid wheat

Nitrogen (N) fertilization is the dominant anthropogenic source of nitrous oxide (N₂O), yet the influence of mineral N source on N₂O emission factors (EF) remains poorly quantified under semiarid irrigation. In a field study in Morocco, four mineral N fertilizers, urea, ammonium nitrate (AMN), urease-inhibited urea (Duramon), and AMN + urea, were evaluated in drip-irrigated wheat at 125 kg N ha⁻¹, alongside an unfertilized control, to test whether fertilizer source alters N₂O emissions and EF relative to the IPCC Tier 1 dry-climate default. Our results show that mineral N source significantly affected cumulative N₂O emissions, EF, and yield-scaled emissions despite comparable grain yields among treatments. Cumulative emissions were 1.84, 1.36, 1.02, and 1.02 kg N ha⁻¹ for urea, Duramon, AMN, and AMN + urea, respectively, versus 0.28 kg N ha⁻¹ in the control; urea emitted 1.82-fold more N₂O than ammonium nitrate at equivalent yield. Corresponding EF values (bootstrap 95% CI) were 1.24% (1.10-1.38) for urea, 0.86% (0.70-1.02) for Duramon, 0.59% (0.42-0.76) for AMN, and 0.59% (0.45-0.74) for AMN + urea. Both urea-based fertilizers exceeded the IPCC Tier 1 default of 0.5% in all bootstrap resamples, whereas nitrate-containing fertilizers bracketed the default. The urease inhibitor reduced cumulative emissions relative to conventional urea but did not significantly reduce yield-scaled emissions. These findings show that mineral N source is a major determinant of N₂O emissions in semiarid irrigated wheat and that non-stratified emission factors may underestimate emissions in urea-dominated systems. Replacing conventional urea with nitrate-containing fertilizers is therefore an immediately actionable strategy without a yield penalty.