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

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 its physicochemical properties were analyzed. Pot experiments were conducted to test Cd immobilization at 0, 1, and 2 mg kg⁻¹ Cd levels with B or FB doses of 0%, 1%, and 3% (w/w) B or FB. FB exhibited higher specific surface area, pore volume, and oxygen-containing functional groups than B. It, enhanced Cd adsorption via mechanisms including surface complexation (-OH, Fe-O), precipitation (CdCO₃), and π-π interactions. Furthermore, FB reduced bioavailable Cd content in soil by 15-28% and shifted Cd speciation from exchangeable forms to Fe/Mn oxide-bound fractions, outperforming B even at lower doses. Additionally, FB improved soil fertility, enzyme activities, and enriched Cd-immobilizing bacteria in the soil, promoting lettuce growth and reducing Cd content in roots (25-40%) and leaves (33-47%). The findings highlighted FB as a cost-effective and sustainable amendment for Cd-contaminated soils, which enhanced adsorption, microbial modulation, and reduced application rates. This study provides critical insights into the dual role of Fe-modified biochar in soil remediation and crop safety, supporting its practical application in sustainable agriculture.