Synergistic Effects of Different Passivation Materials on Soil Cadmium Immobilization and Cadmium Uptake Reduction in Brassica chinensis

To clarify the remediation performance of different passivation materials in lightly cadmium（Cd）-contaminated farmland and their synergistic effects on crop growth, a field experiment was conducted in Kunming using pakchoi（ Brassica chinensis ）. Seven treatments were established, including non-fertilization（CK₁）, traditional fertilization（CK₂）, biochar（BR）, composted organic fertilizer（CP）, Cd-immobilizing mineral amendment（DC）, and their combinations（BR+CP, DC+CP）. The results showed that all passivation treatments improved soil pH value, organic matter, and dissolved organic carbon（DOC）, with CP and DC+CP exhibiting particularly strong effects during the mid-to-late growth stages. Soil available Cd concentrations were significantly reduced across treatments, with BR+CP achieving the lowest level at the mid-growth stage（0.0845 mg/kg）. Cadmium accumulation in pakchoi was also markedly suppressed, with DC+CP showing the greatest reduction（57%）, while CP significantly enhanced biomass, demonstrating a clear “yield promotion-Cd inhibition” synergy. In conclusion, the rational selection and combination of passivation materials can effectively reduce Cd bioavailability, improve soil quality, and simultaneously enhance crop productivity and food safety, providing valuable technical guidance for the green remediation of lightly Cd-contaminated farmland.