Responses of N 2 O, CO 2 , and NH 3 Emissions to Biochar and Nitrification Inhibitors Under a Delayed Nitrogen Application Regime

Greenhouse gas and NH 3 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 N 2 O, CO 2 , and NH 3 emissions of a delayed and reduced N application regime on the Huang-Huai-Hai Plain were investigated. The treatments comprised the control (N 0 ), conventional N at 270 kg N ha −1 (N 270 ) and optimized N application of 180 kg N ha −1 (N 180 ), N 180 + biochar at 7.5 t ha −1 (N 180 B 7.5 ), N 180 + biochar at 15 t ha −1 (N 180 B 15 ), N 180 + DMPP (a nitrification inhibitor; N 180 D), N 180 D + biochar at 7.5 t ha −1 (N 180 DB 7.5 ), and N 180 D + biochar at 15 t ha −1 (N 180 DB 15 ). Reduced N application (N 180 ) lowered N 2 O and NH 3 emissions. Biochar application resulted in a 4–25% and 12–16% increase in N 2 O and NH 3 emissions, respectively. Application of DMPP significantly decreased N 2 O emissions by 32% while concurrently inducing a 9% increase in NH 3 emissions. Co-application of DMPP and biochar significantly reduced the activity of nitrification enzymes (HAD, NOO), resulting in a reduction of 37–38% in N 2 O emissions and 13–14% in NH 3 emissions. No significant differences in CO 2 emissions were observed among the various N treatments except the N 0 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 N 180 DB 15 treatment has the potential to reduce emissions of N 2 O and NH 3 while concurrently enhancing soil fertility (pH, SOC) and wheat yield.