Evaluation of biochar-based phosphate fertilizer for improving soil properties, chili yield, and microbial function

Introduction: Excessive use of chemical fertilizers leads to soil degradation during chili cultivation, particularly in acidic red soils with low phosphorus (P) availability, which limits yield and quality. Methods: In this study, a tobacco stem-derived biochar-based phosphate fertilizer (P-BCL800) was developed to address this problem. Pot experiments with six treatments (blank control; P-BCL800 alone; traditional phosphate fertilizer; and 33%, 66%, and 100% P-BCL800 replacement) were conducted. Results and discussion: The results indicated that all three P-BCL800 substitution treatments (33%, 66%, and 100% P-BCL800 replacement) significantly improved chili yield, photosynthetic efficiency, soil pH, and soil P availability compared to the traditional phosphate fertilizer treatment. Among these, the 66% substitution treatment achieved the highest yield (382 g) and exhibited the best overall performance. It also enhanced alkaline phosphatase activity and increased microbial diversity, including the relative abundance of Proteobacteria and Actinobacteria. Unlike previous studies that primarily focused on yield and soil nutrients, our findings indicate that P-BCL800 regulates microbial community structure and function in acidic red soil-chili systems. These results highlight key drivers (pH, organic matter, and available P) of sustainable cultivation.