Synergistic improvement of soil health and rice safety: A novel pathway for cadmium(II) remediation using co-pyrolyzed biochar from peanut shell and maize straw

Cadmium (Cd(II)), one of the most toxic heavy metals in paddy soils, poses a major threat to food security. In this study, the effects of biochar derived from maize straw (MB), peanut shells (PB), and their copyrolysis (MPB) on soil properties, Cd(II) immobilization, microbial communities, and rice production were evaluated. MPB exhibited superior physicochemical properties relative to mono-feedstock biochars, including higher porosity, higher cation exchange capacity, and greater enrichment of oxygen-containing functional groups (e.g., CO, CC). XRD and SEM analysis showed that MPB had an amorphous carbon structure with decreased crystallinity and a honeycomb-like porous network, providing abundant adsorption sites. Application of MPB significantly increased soil pH, organic carbon, and available K, whereas it decreased CaCl2-extractable Cd(II) by 51.79 % and shifted Cd(II) from the labile to residual fractions. MPB also increased bacterial α diversity, promoted the abundance of beneficial taxa such as Anaerolineaceae and Vicinamibacterales, and strongly reshaped community and environmental relationships. In rice tissues, compared with the control, MPB reduced Cd(II) accumulation by 19.42 % in roots, 23.32 % in stems, 47.18 % in leaves, and 45.56 % in grain, ensuring that Cd(II) levels in grain remained below the national safety threshold. Moreover, MPB improved rice yield (+2.55 %), milling quality, and amylose content. These findings demonstrate that copyrolyzed biochar provides an integrated strategy to simultaneously mitigate Cd(II) risk and increase rice productivity in contaminated paddy soils.