Investigating the potential influence of biochar and traditional organic amendments on the bioavailability and transfer of Cd in the soil–plant system

In this paper biochar (BC) and traditional soil amendments, including press mud (PrM), farm manure (FM), compost (Cmp), poultry manure (PM) and sewage sludge (SS), were evaluated as carbon sources (20 g kg⁻¹ organic carbon) to assess their ability to store soil organic carbon as well as their effects on the bioavailability, transfer and immobilization of Cd in contaminated soil. Wheat (Triticum aestivum L.) was grown on unamended and amended soil (at 2 % organic carbon basis) in a greenhouse experiment and the soil characteristics, AB-DTPA extractable Cd and metal uptake were determined. The influence of the applied organic carbon amendments on the soil properties and accumulation of Cd was evaluated and compared to unamended soil. All of the amendments increased the soil OC significantly with the highest value (1.2 %) with BC followed by PrM (0.98 %) and Cmp (0.86 %). The maximum decrease in the AB-DTPA extractable Cd (43.82 %) was recorded with the BC amendment followed by Cmp (18.16 %), while FM and PrM amendments increased the Cd availability up to 19.92 and 4.45 %, respectively. The uptake of Cd by Triticum aestivum L. was increased with all of the amendments except for BC and Cmp, which showed significant decreases, and the maximum transfer factor was found in SS followed by PrM, PM and FM. The soil organic carbon (OC), cation exchange capacity (CEC) and pH were negatively correlated with the AB-DTPA extractable Cd in post-experiment soil. The results obtained from this experiment suggest that organic carbon from biochar (BC) can be used to increase the soil OC stock, and it is also effective for the in situ immobilization/remediation of Cd, thus improving the physico-chemical properties of soil and leading to increased plant growth.