A Novel Iron-Modified Corn Straw Biochar Enhanced Cd Immobilization and Reduced Cd Uptake in Lettuce and the Mechanisms Involved

Cadmium(Cd)contamination poses significant risks to agricultural productivity and ecosystems, necessitating effective remediation strategies. This study evaluated the efficacy of iron (Fe)-modified corn straw biochar (FB) in immobilizing Cd and reducing its uptake in lettuce, compared to raw biochar (B). FB was synthesized by pyrolyzing Fe(NO₃)₃-treated corn straw and characterized for physicochemical properties. Pot experiments tested Cd immobilization at 0, 1, and 2 mg kg⁻¹ Cd levels with 0%, 1%, and 3% (w/w) B or FB applications. Results demonstrated that FB exhibited higher specific surface area, pore volume, and oxygen-containing functional groups than B, enhancing Cd adsorption via mechanisms including surface complexation (-OH, Fe-O), precipitation (CdCO₃), and π-π interactions. FB reduced soil bioavailable Cd by 15–28% and shifted Cd speciation from exchangeable to Fe/Mn oxide-bound fractions, outperforming B even at lower doses (1% FB ≈ 3% B). Additionally, FB improved soil fertility, enzyme activities, and enriched Cd-immobilizing bacteria , promoting lettuce growth and reducing Cd content in roots (25–40%) and leaves (33–47%). The findings highlight FB as a cost-effective and sustainable amendment for Cd-contaminated soils, combining enhanced adsorption, microbial modulation, and reduced application rates. This study provides critical insights into Fe-modified biochar’s dual role in soil remediation and crop safety, supporting its practical application in sustainable agriculture.