Responses of N₂O, CO₂, and NH₃ Emissions to Biochar and Nitrification Inhibitors Under a Delayed Nitrogen Application Regime

Greenhouse gas and NH₃ emissions are exacerbated by the inappropriate timing and excessive application of nitrogen (N) fertilizers in wheat cultivation in China. In this study, the impacts on N₂O, CO₂, and NH₃ emissions of a delayed and reduced N application regime on the Huang-Huai-Hai Plain were investigated. The treatments comprised the control (N₀), conventional N at 270 kg N ha⁻¹ (N₂₇₀) and optimized N application of 180 kg N ha⁻¹ (N₁₈₀), N₁₈₀ + biochar at 7.5 t ha⁻¹ (N₁₈₀B_7.5), N₁₈₀ + biochar at 15 t ha⁻¹ (N₁₈₀B₁₅), N₁₈₀ + DMPP (a nitrification inhibitor; N₁₈₀D), N₁₈₀D + biochar at 7.5 t ha⁻¹ (N₁₈₀DB_7.5), and N₁₈₀D + biochar at 15 t ha⁻¹ (N₁₈₀DB₁₅). Reduced N application (N₁₈₀) lowered N₂O and NH₃ emissions. Biochar application resulted in a 4–25% and 12–16% increase in N₂O and NH₃ emissions, respectively. Application of DMPP significantly decreased N₂O emissions by 32% while concurrently inducing a 9% increase in NH₃ emissions. Co-application of DMPP and biochar significantly reduced the activity of nitrification enzymes (HAD, NOO), resulting in a reduction of 37–38% in N₂O emissions and 13–14% in NH₃ emissions. No significant differences in CO₂ emissions were observed among the various N treatments except the N₀ treatment. Application of DMPP alone did not significantly affect grain yield. However, biochar, in combination with DMPP, effectively increases grain yield. The findings suggest that the N₁₈₀DB₁₅ treatment has the potential to reduce emissions of N₂O and NH₃ while concurrently enhancing soil fertility (pH, SOC) and wheat yield.