Effect of Biochars from Rice Husk, Bran, and Straw on Heavy Metal Uptake by Pot-Grown Wheat Seedling in a Historically Contaminated Soil

The effect of biochar amendment of a multi-element contaminated soil on the transfer and accumulation of Cd, Zn, Pb, and As in wheat was investigated in this study. Addition of biochars from rice residues (straw, husk, and bran) significantly decreased shoot Cd, Zn, and Pb concentrations by up to 71%, 37%, and 60%, respectively, but increased As by up to 199%. Biochar additions decreased the NH4NO3-extractable concentrations of Cd, Zn, and Pb in soil by 23 to 81%, 29 to 94%, and 31 to 92%, respectively, especially straw-char treatment, though biochar treatment increased the concentration of As by 64 to 2650%. A decrease in biochar particle size generally favored the immobilization of Cd, Zn, and Pb in soil and reductions in their accumulation in wheat shoot, but this was reversed for As. Increases of up to 21%, 70%, 59%, and 40% in shoot biomass, root length, and shoot P and K levels, respectively, of wheat seedlings were caused by biochar amendments. Biochar has the potential to reduce accumulations of Cd, Zn, and Pb in wheat shoot and improve its growth.