Effect of biochar on Pb, Cd and Cr availability and maize growth in artificial contaminated soil

This study was performed to investigate the effect of biochar manufactured from agriculture residues for the stabilization of lead, cadmium and chromium (Pb, Cd and Cr) in artificially contaminated soil. A surface loamy sand soil was spiked with Pb, Cd and Cr at 200, 400 and 600 mg kg(-1). Thereafter, the spiked soil was treated with biochar at different rates of 0.0, 1.0, 2.5, 5.0 and 10% (weight basis) and incubated for 30 days. The treated soil was cultivated with maize plant (Zea mays) lasting 30 days. Addition of biochar significantly increased the soil reaction (pH), organic matter (OM) and nutrient content of nitrogen, phosphorus and potassium (N, P and K). Moreover, the addition of biochar considerably decreased the solubility of Pb and Cd in terms of water soluble, exchangeable (extracted by ammonium nitrate), physiological based extraction test (PBET) and toxicity characteristics leaching procedure (TCLP) extracts. The highest reduction of expendable Pb and Cd were 28.68% and 85.14%, respectively. On the other hand, addition of biochar might facilitated Cr solubility through the transformation of Cr(III) into Cr(VI) due to increasing soil pH, and increased its uptake by maize plant. The phytotoxicity test revealed that biochar significantly increased maize biomass (shoots and roots), especially with applications of 5% and 10% treatments. Our findings provide evidence that biochar application decreased Pb and Cd toxicity by immobilizing them into more stable forms and improved soil quality. However, attention should be paid when treating the soil that is co-contaminated by Cr with biochar.