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 (N180B7.5), N180 + biochar at 15 t ha−1 (N180B15), N180 + DMPP (a nitrification inhibitor; N180D), N180D + biochar at 7.5 t ha−1 (N180DB7.5), 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.