Combined Biochar and Bentonite Application for Immobilization of Cadmium and Brassica Chinensis L. Growth in Contaminated Soil

This study aims to investigate the efficiency of bentonite and biochar in immobilizing cadmium (Cd) and mitigating the stresses of Brassica Chinensis L. in Cd-contaminated soil. The crop of Brassica chinensis L. was applied 5% (w/w) mono- biochar (C), mono- bentonite (B), and integrated biochar and bentonite (1:1 = W: W, BC). The change in soil properties, DTPA-extractable Cd, fractionation of Cd in soil, bioaccessible Cd in crop, and plant growth in crop were examined. The pH, cation exchange capacity (CEC), soil organic carbon (SOC), and total phosphorus (TP) of soil were improved in amended soil compared with unamended (control). The integrated application of BC exhibited maximum reduction of 38.60% in DTPA-extractable Cd of soil followed by 24.56% from C treatment (mono- biochar) and 15.80% from B treatment (mono- bentonite) compared to control. The concentration of exchangeable Cd declined by 7.81–20.31% however residual Cd was improved by 23.40–65.96% in sole application of B and C and integrated application of BC. Furthermore, concentrations of Cd in the shoots were dwindled by 83.02% and 72.77% in the roots of Brassica chinensis L., which boosted biomass of Brassica chinensis L. was boosted to 5.177 g/plant by BC treatments. It is concluded that bentonite and biochar have potential capacity to alleviate the exposure risk of cadmium to crops. The integrated application of bentonite and biochar was most effective for mitigation of harmful effects of Cd. This study has established a theoretical basis for further research on immobilization of heavy metals in agricultural soils.