An assessment of integrated amendments of biochar and soil replacement on the phytotoxicity of metal(loid)s in rotated radish-soya bean-amaranth in a mining acidy soil

Knowledge is insufficient on feasible remediation techniques to agricultural soils contaminated by multiple heavy metal(loid)s with elevated concentrations and extreme acidy from acid mine drainages (AMD). We aimed to elucidate the effect of integrated biochar (BC) and soil replacement on improving the mining soil properties and then alleviating the phytotoxicity of As, Pb, Cd, Cu, and Zn on radish (Raphanus sativus L.)-soya bean (Glycine max Merr.) -amaranth (Amaranthus tricolor L.) rotation and the potential risk of crops to human health. Biochar and soil replacement showed outstanding effects on improving soil properties by increasing soil pH values, reducing available metal(loid)s, and enhancing the activity of catalase, urease and acid phosphatase. Also, the integrated technique regulated the physiological disorders of crops caused by metal(loid)s, specifically increasing chlorophyll content and reducing malondialdehyde (MDA) in the three crops, and reducing the content of metal(loid)s in edible parts of plants. The combination of biochar and soil replacement exhibited better remediation effect than the single application of biochar or soil replacement, which played different roles in remediating mining farmland. Biochar exhibited efficacy in soil pH amelioration, metal stabilization and soil enzyme activity enhancement, while soil replacement alleviated metal(loid)s stress through the dilution effect. Among the 8 treatments, only biochar combined with 35% (S35BC) and 50% (S50BC) of replaced soil could achieve the safe production of the three crops under the three-season crop rotation.