Effects of two biochar types on nitrous oxide emissions, soil properties, microbial activity, and crop yield in Chinese cabbage fields

This study examined how biochar application alters N 2 O emissions along with changes in soil physicochemical properties, enzyme activities, and microbial community composition through a 14-week summer–autumn field experiment in upland Chinese cabbage cultivation. The biochars used in this study were chicken manure biochar (CMB) and pepper stem biochar (PSB). CMB was relatively rich in nitrogen, whereas PSB exhibited a low H/C ratio and a high C/N ratio. The effectiveness of biochar was evaluated based on its application rate (1 or 2 t/ha) and its combined use with chemical fertilizers. Biochar application effectively countered the soil pH reduction induced by chemical fertilizers. CMB increased nutrient supply and crop productivity, whereas PSB improved soil carbon retention and cation exchange capacity. Compared with chemical fertilizer alone, CF + PSB2 (2 t/ha PSB with chemical fertilizer) reduced cumulative N 2 O-N emissions by 41.9%. In contrast, CMB treatments increased N 2 O emissions but enhanced Chinese cabbage yield by 1.16-fold, reflecting their higher nitrogen content. Combined application of CMB or PSB with chemical fertilizers enhanced the activities of three key soil enzymes (dehydrogenase, alkaline phosphatase, and β -glucosidase), as opposed to using chemical fertilizer alone, although excessive biochar application inhibited some enzyme activities. Carbon and nitrogen availability shaped microbial community structure, particularly Proteobacteria and Bacteroidetes . By incorporating analyses of soil chemistry, enzyme activity, and microbial communities, this study provides comprehensive insight into the role of biochar in greenhouse gas mitigation and soil health enhancement.