Two years impacts of rapeseed residue and rice straw biochar on Pb and Cu immobilization and revegetation of naturally co-contaminated soil

Biochar continues to gain significant interest in remediation and revegetation of agricultural soils contaminated with potentially toxic elements. Two-year impacts of rapeseed residue and rice straw biochars on Pb and Cu immobilization and revegetation of naturally co-contaminated soil were studied. The extraction techniques namely European Community Bureau of Reference (BCR) sequential extraction procedure, the toxicity characteristics leaching procedure (TCLP), and CaCl2 extraction were performed to assess Pb and Cu mobility following biochar incorporation. The obtained results revealed that soil pH mostly sustained, with a slight increase of 0.2 units on average. Sequential extraction results exhibited a substantial reduction in the acid soluble forms of Pb and Cu by 57.56% and 54.18% respectively in two years. The immobilized Pb and Cu were effectively transformed into residual (stable) forms; accordingly, the phytoavailable pools of Pb and Cu were reduced after adding biochar. The concentration of Pb and Cu in plants were significantly decreased by 40.81% and 56.14% respectively, with no noticeable variations observed in dry wheat biomass. Due to their stability, rapeseed residue and rice straw biochars produced at high temperature were more effective in immobilizing Pb and Cu as compared to low-temperature biochars. The varying efficiencies of the biochars to immobilize Pb and Cu were attributed to the composition and the degree of ageing of biochars in the amended soils.