Hematite-modified calcined bamboo biochar composite enhances soil biochemical functioning and reduces antimony phytoavailability in agricultural soil

Antimony (Sb) contamination severely threatens soil quality, ecological functioning, and crop productivity in agricultural systems. This study investigated the potential of a calcined bamboo biochar–hematite composite (BHC) to reduce Sb phytoavailability and improve soil biochemical functioning in Sb-contaminated agricultural soil cultivated with maize. Among all treatments, BHC reduced EDTA-extractable soil Sb by 26% and decreased shoot Sb concentration by 40.6% relative to the unamended control (CK) and exhibited the lowest Sb translocation indices. Sequential extraction demonstrated the transformation of labile Sb fractions into oxide-bound and residual forms, indicating enhanced Sb stabilization in soil. FTIR and XPS analyses suggested that Sb immobilization was associated with surface complexation involving Fe–OH and oxygen-containing functional groups (OFGs) on the BHC surface. Importantly, BHC enhanced soil biochemical functioning, as indicated by increased activities of urease (27.9%), alkaline phosphatase (81.4%), and sucrase (16.6%), resulting in the highest soil geometric mean enzyme activity (GMEA) among all treatments. Simultaneously, BHC alleviated Sb-induced physiological stress in maize, as indicated by reduced antioxidant enzyme activities together with improved chlorophyll content and biomass production. Collectively, these findings highlight the potential of BHC as a multifunctional amendment that integrates Sb stabilization with improvements in soil biochemical functioning and plant performance in contaminated agricultural soils.