[Gaseous Nitrogen Emission from Soil After Application of NH₄⁺-N Loaded Biochar]

To safely and effectively transfer NH₄⁺-N from eutrophic water to soil, biochar was applied to adsorb NH₄⁺-N from wastewater, and this NH₄⁺-N loaded biochar (N-BC) was subsequently used as a soil amendment. Understanding the influence of N-BC on N₂O-N emission and NH₃-N volatilization is important for both decreasing the application of chemical fertilizers and reducing gaseous nitrogen loss from soil. In this study, experiments were conducted in soil columns with four treatments, namely CK (no fertilizer), NPK (chemical fertilizer), N-BC+PK (NH₄⁺-N loaded biochar+chemical fertilizer), and BC+NPK (biochar+chemical fertilizer). Compared to both the NPK and BC+NPK treatments, N-BC+PK significantly reduced the cumulative N₂O-N emissions and NH₃-N volatilization, as well as the total gaseous nitrogen loss from the soil (P<0.05). Relative to NPK and BC+NPK, cumulative N₂O-N emissions decreased by 33.62% and 24.64%, cumulative NH₃-N volatilization decreased 70.64% and 79.29%, and the cumulative total gaseous nitrogen loss decreased by 64.97% and 73.75%. In particular, BC+NPK significantly enhanced the cumulative NH₃-N volatilization. Furthermore, the N₂O-N emission flux and NH₃-N volatilization rate were significantly positively correlated with the NH₄⁺-N concentration, NO₃^--N concentration, and pH of soil (P<0.01). Overall, using NH₄⁺-N loaded biochar can significantly decrease N₂O-N emissions and NH₃-N volatilization, relative to the traditional application combining biochar and chemical fertilizer. This research provides solid theoretical support and data for the application of NH₄⁺-N loaded biochar in soil, to reduce gaseous nitrogen loss.