Biochar combined with chemical fertilizer increases maize yield and soil ecosystem multifunctionality in an intercropped maize-soybean

To investigate the effects of biochar addition on maize growth and soil ecosystem multifunctionality in a maize-soybean intercropping system, a two-year field experiment was conducted in Xianning City, Hubei Province, from 2023 to 2024. The study examined two planting patterns—monoculture maize (MM) and intercropped maize and soybean (SM)—and two fertilization regimes—conventional chemical fertilizer (CF) and biochar combined with chemical fertilizer (BF). Parameters assessed included maize growth, soil physicochemical properties, microbial diversity, and ecosystem multifunctionality. In terms of cropping system, compared with monoculture maize, intercropping significantly increased maize root length density in the 0-30 cm soil layer by 21.58%-32.24%, reduced soil bulk density by 6.31% in the 10-20 cm layer, increased soil organic carbon content by 3.51% and 13.01% in the 0-10 cm and 20-30 cm layers, respectively, and raised total nitrogen content by 8.96% and 12.13% in the 10-20 cm and 20-30 cm layers, respectively. In terms of fertilizer treatment, compared with conventional chemical fertilizer, the combination of biochar and chemical fertilizer increased maize root length density by 5.84%-11.42% in the 0-30 cm layer, reduced soil bulk density by 4.77% in the 10-20 cm layer, and increased soil organic carbon content by 4.54% and 14.11% in the 0-10 cm and 20-30 cm layers, respectively. Relative to MM-CF, intercropping with chemical fertilizer (SM-CF) increased maize equivalent yield by 33.56%, and enhanced the soil ecosystem multifunctionality index by 101.63%-119.91% in the 0-30 cm layer. Intercropping with biochar and chemical fertilizer (SM-BF) further increased equivalent yield by 49.24% and boosted the multifunctionality index by 134.59%-238.63%. A random forest model identified root biomass as the most influential factor affecting soil ecosystem multifunctionality. These findings suggest that biochar combined with chemical fertilizer improves soil structure, enhances nutrient accumulation, and increases microbial diversity by promoting maize root growth under intercropped conditions, thereby synergistically enhancing both maize yield and soil ecosystem functions, and contributing to sustainable agricultural development.