The Effects of Biochar and Intercropping on the Cd, Cr and Zn Speciation in Soils and Plant Uptake by Machilus pauhoi.

A greenhouse pot experiment with biochar (BC) applied at 0%, 1%, 4% and 8% (w/w) in monoculture and intercropping settings was used to investigate Cd, Cr and Zn speciation in contaminated soils, the growth of two different plant types, and the heavy metal concentrations within these plants. The results showed that BC application increased the soil pH, decreased the bioavailability of Cd, Cr and Zn, significantly increased the dry biomass of Cassia occidentalis and Machilus pauhoi shoots and slightly increased the root biomass. Both BC addition and intercropping decreased the Cd, Cr and Zn contents in the M. pauhoi shoots and roots, but the effect of BC addition was more significant than the effect of intercropping. The Cd, Cr and Zn uptake by M. pauhoi shoots was reduced by up to 93.91%, 96.41% and 76.76%, respectively, when the concentration and bioavailability of Cd, Cr, and Zn were reduced by using the combination of intercropping and BC application. This treatment resulted in the greatest reduction efficiency, and resulted in a shoot biomass increase of M. pauhoi of up to 122.52% compared to the control (M. pauhoi monoculture). These results could be used as a reference for the promotion of M. pauhoi growth and the utilization of contaminated land.