Effect of Apple Pruning Residue Biochar on Chemical Forms, Mobility Factor Index (MF) and Reduced Partition Index (IR) of Heavy Metals in a Contaminated Soil

In order to study the effect of apple (Golden delicious variety) pruning residue biochar on chemical forms of Cd, Pb, Cu and Zn in a contaminated soil, an experiment was conducted as a factorial in a completely randomized design (CRD) in three replications with 4 levels of biochar (0, 2, 5 and 10 %) and 4 levels of incubation time (1, 2, 4 and 8 weeks). Chemical distribution of metals in soil was determined using Tessier sequential extraction method during the mentioned incubation times and the reduced partition index (IR) and mobility factor (MF) of the metals were calculated. Application of the biochar significantly (p ≤ 0.05) decreased the exchangeable and carbonate fractions and increased organic and iron and manganese oxide bound fractions in comparison to the control treatment. With increasing the biochar level and incubation time, the IR values were increased, but MF values decreased, demonstrating a decrease in the mobility of metal in soils. It was concluded that the addition of the apple biochar in soil may led to transformation of the metals from unstable forms (e.g. exchangeable and carbonate forms) to stable forms (e.g. iron and manganese oxide bound and residual forms), and consequently decreased the mobility of the metals in soil.