Optimizing biochar use under different soil pH conditions for sustainable crop production and soil carbon sequestration

Abstract Biochar has been widely recognized as a soil amendment capable of improving soil quality and enhancing carbon sequestration. In South Korea, the interaction between biochar application rate and contrasting initial soil chemical conditions remains insufficiently understood. This study evaluated the agronomic and soil carbon sequestration to pepper residue biochar under different soil pH conditions (Soil A: pH 5.8; Soil B: pH 6.8) in a field cultivation of Chinese cabbage. The biochar was prepared from pepper residue through pyrolysis at 400 °C for 2 h. Treatments included no fertilizer, inorganic fertilizer (N-P 2 O 5 -K 2 O = 32.0-7.8-19.8 kg 10a -1 ), and biochar applied at 100, 200, 300, and 500 kg 10a -1 combined with inorganic fertilizer. In Soil A, soil organic carbon stock increased with increasing biochar rate, reaching 36.8 t C ha -1 at 500 kg 10 a -1 . In contrast, in Soil B, SOC stock increased up to 33.8 t C ha -1 at 300 kg 10 a -1 but showed limited gains at higher rates. Crop yield peaked at 300 kg 10 a -1 in Soil A (6,403 kg 10 a -1 ) and at 200 kg 10 a -1 in Soil B (4,200 kg 10 a -1 ). The results demonstrate that biochar efficiency in crop productivity and carbon accumulation is strongly influenced by initial soil chemical properties rather than application rate alone. When both crop productivity and soil carbon accumulation are considered, 200–300 kg 10 a -1 provides a balanced management strategy under the conditions examined. This study highlights the importance of soil-specific optimization of biochar application for sustainable agricultural carbon management.