Objective The aims to investigate the effects of biochar and organic fertilizer application on N₂O emission and NH₃ volatilization in the red soil of the newly reclaimed terraced mountain.

Methods The planting experiment of two cabbage crops in the plot was conducted. The 7500 kg hm⁻² biochar (B) and 7100 kg hm⁻² organic fertilizer (F) were applied on the basis of CK, and 3 treatments were set up, each treatment was repeated 3 times. A total of 9 experimental plots were randomly designed. The changes of N₂O emission, NH₃ volatilization, cationic exchange capacity (CEC), functional groups, total organic carbon, water-soluble organic carbon, microbial biomass carbon content and aggregate stability of soil were measured. The relationship between nitrogen gasification loss and soil properties was analyzed to reveal the mechanism of application of biochar, organic fertilizer and nitrogen gas volatilization.

Results The application of biochar and organic fertilizer significantly reduced the cumulative emission of N₂O and NH₃ volatilization in soil, and there was no significant difference in the emission reduction effect of the two, and the emission reduction effect of organic fertilizer on NH₃ volatilization was significantly better than that of biochar (P < 0.01). The CEC contents, functional groups (O-H, NH, C=O, C=N, C=C), total organic carbon and water-soluble organic carbon in soil were significantly increased after application of biochar and organic fertilizer, and the effects of biochar on increasing soil CEC, functional groups and total organic carbon contents were significantly better than those of organic fertilizer. The effects of organic fertilizer on water-soluble organic carbon, microbial biomass carbon content and aggregate stability were significantly better than those of biochar. Redundancy analysis showed that soil microbial biomass carbon, percentage of aggregates > 0.25 mm and water-soluble organic carbon were the main factors affecting soil N₂O emission and NH₃ volatilization.

Conclusion The application of organic fertilizer can increase the content of soil microbial biomass carbon and water-soluble organic carbon, which is conducive to the formation and stability of soil large aggregates, and inhibit the volatilization of soil nitrogen gas. The effect of organic fertilizer on inhibiting soil nitrogen volatilization was better than that of biochar.