Effects of reduced nitrogen application combined with biochar and biochar-based fertilizer application on N₂O emissions and NH₃ volatilization from protected vegetable fields in red soil regions

Excessive nitrogen fertilization not only inhibits crop growth but also induces N₂O emissions and NH₃ volatilization, contributing to environmental pollution. Biochar and biochar-based fertilizers show potential in soil improvement and emission reduction. This study investigated the impacts of different straw-derived biochar application methods combined with chemical fertilizer reduction on N₂O emissions and NH₃ volatilization in a red soil vegetable greenhouse in Changsha, Hunan Province. Four treatments were established: no fertilization (CK), conventional fertilization (CON), 20% nitrogen reduction + biochar-based fertilizer (BF), and 20% nitrogen reduction + biochar (BC). N₂O emissions were monitored via gas chromatography, NH₃ was collected using the closed chamber method, and soil nitrogen content and crop yield were measured. Results demonstrated that BF and BC treatments significantly reduced N₂O emissions by 27.80% and 12.27%, respectively, with BF exhibiting a 17.70% greater reduction than BC. The N₂O emission factor of BF decreased by 33.56% compared to CON, outperforming BC by 33.10%. NH₃ volatilization under BF and BC declined by 20.47% and 14.26%, respectively, with BF reducing the NH₃ volatilization emission factor by 25.40%, 16.81% lower than BC. BF increased nitrogen use efficiency by 50.91%. Soil NH₄⁺-N decreased by 18.03% and 11.40% under BF and BC, respectively, while NO₃^--N showed no significant variation. Random forest analysis identified soil NH₄⁺-N, NO₃^--N, and temperature as key drivers of N₂O and NH₃ emissions. Fresh weight yields remained consistent across treatments. BF reduced N₂O emissions per unit yield by 28.12%. In conclusion, nitrogen reduction combined with biochar or biochar-based fertilizer effectively mitigates N₂O emissions and NH₃ volatilization in greenhouse vegetable systems, with biochar-based fertilizer demonstrating superior performance.