The biochars are efficient adsorbent of heavy metals. However, the type of biochar species determines the effectiveness of biochars for immobilization of heavy metals. In this experiment, we mixed different biochars in variable mass ratios and evaluated their effects on plant growth and bioavailability of heavy metals. The results revealed that amendment of single and mixed biochars has increased pH, EC, available P and K of soil. The straw block biochar with maize straw biochar at a mass ratio of 1:2 (SDM) has significantly decreased Pb and Cu concentration in soil. The straw block biochar with maize straw biochar at a mass ratio of 2:1 (DSM) has highly increased the dry biomass of Chinese cabbage than single biochar or control, whereas plant physiological properties were mostly not affected. It is concluded that peanut shell biochar with maize straw biochar at a mass ratio of 2:1 (DPS) and DSM have significantly decreased Pb, Zn and Cu concentration in plants. The single peanut shell biochar has significantly decreased the plant Cd concentration. The ability of transport of heavy metals in Chinese cabbage was in the sequence of Cd > Zn > Cu > Pb. The mixing of different biochars has decreased the concentration of heavy metals in plants more effectively than single biochar.
Keywords: Mixed biochars; bioavailability; heavy metals; in-situ remediation; plants physiology.