Effects of biochar application on nitrogen transformation and N₂O emission in a coastal saline-alkali soil

The application of biochar can improve soil fertility and benefit sustainable agricultural development and carbon neutrality simultaneously. To better understand the effects of biochar addition on nitrogen transformation and N₂O emission in a coastal saline-alkali soil and its potential mechanisms, we conducted a 60-day laboratory incubation experiment with six treatments, i.e., ammonium sulfate (N 150 mg·kg^-1), ammonium sulfate + 0.4% (weight/weight) biochar, ammonium sulfate + 0.6% biochar, ammonium sulfate + 0.8% biochar, ammonium sulfate + 1.6% biochar, and ammonium sulfate + 0.2% biochar and 0.2% organic fertilizer (based on equivalent N basis). The results showed that soil nitrogen transformation was mainly affected by biochar addition at the early stage of incubation. Biochar addition significantly increased the contents of nitrate and ammonium. Biochar addition significantly increased soil net nitrification rate, but the magnitude of such increases decreased with increasing biochar addition level. Similar temporal change patterns of N₂O emissions were observed in all treatments, and the N₂O emissions mainly occurred in the first 30 days of incubation. Compared with the CK, biochar addition significantly reduced the cumulative N₂O emission, and the decrement increased with increasing biochar addition levels. In conclusion, the effects of biochar and nitrogen fertilizer addition on soil nitrogen transformation and N₂O emission varied with the application rate. Biochar addition with a rate of 0.8% (W/W) increased soil inorganic nitrogen content and decreased soil N₂O emission. It could provide theoretical basis and reference for the formulation of reasonable plans for the improvement and utilization of biochar in coastal saline-alkali soil.