Interactive effects of biochar types and <i>Bacillus velezensis</i> inoculation on soil properties, microbial communities and wheat performance under greenhouse conditions

Abstract Agricultural intensification has led to soil degradation, reducing fertility and microbial diversity, compromising long‐term productivity. Biochar and plant growth‐promoting rhizobacteria (PGPR) are proposed as sustainable soil amendments, but their combined effects in agricultural semi‐arid soils are poorly understood. This study assessed the interactive effects of poultry manure‐derived biochars produced at 500°C (BC500) and 700°C (BC700), with and without Bacillus velezensis inoculation, on soil chemical properties, enzymatic activities, microbial communities and wheat ( Triticum aestivum ) performance under greenhouse conditions. The effects of biochar were the dominant drivers across all variables analysed, whereas those of PGPR inoculation were less evident. Biochar addition significantly altered soil chemistry, increasing pH, cation exchange capacity and nutrient availability. Enzymatic activities related to C, N and P cycling were also stimulated, with BC500 enhancing β‐glucosidase activity and BC700 promoting phosphomonoesterase and xylosidase activities. High‐throughput sequencing revealed that biochar and PGPR modulated microbial community structure and diversity. The BC500 treatments were associated with Planctomycetota , whereas the BC700 enriched Actinobacteriota , Proteobacteria and Firmicutes . PGPR inoculation increased Shannon diversity and evenness, suggesting an enhanced microbial balance, although its persistence appeared to be limited. Wheat responses differed according to biochar type: BC500 did not significantly affect performance compared with the control, whereas BC700 reduced shoot and root biomass, grain dry weight and grain number. B. velezensis inoculation modestly improved root growth and grain biomass, particularly in the absence of biochar, but did not consistently interact synergistically with biochar amendments. Finally, multivariate analyses suggest that the chemical changes induced in the soil by biochar addition are likely the main drivers of wheat performance in these environments. In addition, the results indicate that the effects of biochar depend strongly on pyrolysis temperature, with moderate‐temperature biochars preserving soil functionality while maintaining crop productivity comparable to the control. The limited effects of B. velezensis highlight the need for improved inoculation strategies to ensure long‐term persistence. These findings emphasise the importance of tailoring biochar properties and microbial applications to local soil conditions for sustainable crop management.