Mitigating continuous cropping challenges in alkaline soils: The role of biochar in enhancing soil health, microbial dynamics, and pepper productivity

Long-term continuous cropping of pepper has led to a decline in soil quality and an increase in pests and diseases, severely constraining yield and fruit quality. Biochar, a soil amendment with multiple regulatory functions, has been widely used to improve soil conditions. However, its potential mechanisms for mitigating continuous cropping obstacles and its long-term effects in alkaline soils remain insufficiently elucidated. In this study, a two-year field experiment was conducted in Ningxia, China, evaluating five biochar application rates (0 %, 0.5 %, 1 %, 2 %, and 4 %) to comprehensively assess its impacts on plant physiological traits, soil nutrient status, and microbial community dynamics under continuous cropping conditions. Results showed that moderate biochar application (2 %) elicited the most pronounced benefits in the second year, significantly enhancing soil organic matter (by 46.5 %), available potassium (43.0 %), available phosphorus (57.7 %), root activity (159.0 %), microbial biomass carbon (131.1 %), and microbial biomass phosphorus (133.0 %). Concurrently, it decreased soil pH (by 3.3 %), root hydrogen peroxide levels (34.3 %), and proline content (31.4 %). At the microbial level, biochar amendment substantially increased the abundance of Sphingomonas and Pseudomonas , suppressed populations of Acidobacteria and Fusarium , and promoted greater richness and complexity within bacterial and fungal co-occurrence networks. Correlation analyses identified available potassium, available phosphorus, soil urease activity, and hydrogen peroxide levels as critical determinants of pepper yield. Collectively, biochar application enhanced pepper yield by 57.8 % and vitamin C content by 61.6 %, primarily through stimulating root growth, mitigating oxidative stress, improving soil nutrient availability, and fostering the proliferation of beneficial microbes antagonistic to pathogens. These findings emphasize the necessity of optimizing biochar application strategies by accounting not only for its soil-mediated effects and persistence but also for its temporally delayed regulatory influences. This work provides novel mechanistic insights and a robust scientific foundation for the precise and sustainable utilization of biochar to overcome continuous cropping challenges in alkaline soils. • Biochar alleviates pepper cropping obstacles with low promotion and high inhibition level. • The initial application of biochar may limit nitrogen availability in soil. • Biochar promotes microorganisms that antagonize pathogens. • Biochar produced better results in the second year than in the first. • Biochar alleviates continuous cropping barriers by reducing H 2 O 2 content in plants.