Abstract:This experiment explored the effects of the application of biochar-based fertilizer on the pH and exchange capacity of the acidic soil in pomelo orchard, and the laboratory culture experiments were conducted for 60 days. In the experiment, no fertilizer control (CK), single application of urea (N), rice straw biochar-based fertilizer (BR) and bamboo biochar-based fertilizer (BB) at four dosage gradients (2.5, 5, 10 and 20 g/kg) were set up, and urea was applied in all treatments. The results showed that with the development of culture experiment, the soil pH value of BR and BB increased first and then decreased, and the contents of exchangeable acid and base ions increased. After 60 days of culture, the improving effects of BR and BB on soil pH, exchangeable acid, exchangeable aluminum, CEC and base saturation became more obvious with the increasing of the dosage of BR and BB, and the effect of BR was better than that of BB. Compared with N treatment, in the BR and BB treatments, the soil pH increased by 0.24~3.43 and 0.21~3.40 units, the exchangeable acid decreased by 45.55%~97.25% and 34.01%~96.70%, the exchangeable aluminum decreased by 46.95%~99.75% and 38.99%~99.00%, the soil CEC increased by 7.02%~170.74% and 6.52%~134.90%, the base saturation increased by 29.40%~51.61% and 32.08%~53.90%, respectively. The application of biochar-based fertilizer could improve the pH of acidic soil, reduce exchangeable acid, greatly reduce exchangeable aluminum, and improve soil CEC and base saturation. Therefore, the optimum amount of biochar-based fertilizer for the acid soil of pomelo orchard was about 2.5~5.0 g/kg, and the effect of rice straw biochar-based fertilizer was better than bamboo biochar-based fertilizer. This experiment provided a scientific basis for the treatment of the acidified soil in pomelo orchard.