Synergistic application of biochar with organic fertilizer positively impacts the soil micro-food web in sandy loam soils

Effective application of biochar is critical to improving soil health, but its intricate biological impact on the soil micro-food web remains poorly understood. To address this, a field experiment with four treatments - inorganic fertilization (IF), organic fertilization (OF), inorganic fertilization with biochar addition (B + IF), and organic fertilization with biochar addition (B + OF) - was conducted within a wheat cropping system on a sandy loam soil. The study aimed to elucidate the role of biochar-induced changes in abiotic factors and plant root inputs in shaping the soil micro-food web. Results showed that the effects of biochar on the soil micro-food web varied depending on the fertilization context. Under inorganic fertilizer, biochar strongly increased the abundance of total microbes and total nematodes, but reduced the biomass of omnivores-predators. However, biochar combined with organic fertilizer had a positive effect on the abundance and biomass of total microbes as well as the biomass of total nematodes and omnivores-predators. In addition, biochar with inorganic fertilizer affected the abundance of microbes and nematodes through direct pathways and indirectly affected microbial biomass and abundance mediated by reducing NH4+-N and DOC content. In contrast, in organic fertilization, the improvement of root biomass and soil pH were the most direct drivers of variation in microbial abundance. These findings highlight the potential of biochar as a strategic amendment to optimize soil micro-food web dynamics, with fertilizer type playing a critical role in determining its effectiveness. The combination of biochar with organic fertilizer provides a basis for improving soil health and supporting sustainable agricultural practices on sandy loam soils.