Cadmium immobilization in the soil and accumulation by spinach (Spinacia oleracea) depend on biochar types under controlled and field conditions

In the present study, efficiency of different biochars (BCs) on cadmium (Cd) immobilization and its bioavailability to spinach were investigated. In the first experiment, Cd-spiked soil was amended with treatments (T1 = control, T2 and T3 = cotton stalk biochar (CBC) 2% and 5%, T4 and T5 = rice straw biochar 2% and 5%) and incubated for 120 days. In the second experiment, spinach was grown in pots using three soils (a normal soil, a Cd-spiked soil, and a sewage-irrigated soil) after application of CBC and rice straw biochar (RBC) (2% w/w each) in each soil. In the field experiments, spinach was grown at two sites with six treatments including T0 = control, T1 and T2 (RBC 5 and 10 ton ha−1), T3 and T4 (CBC 5 and 10 ton ha−1). The results of our experiments showed a significant impact of BCs on soil pH, EC, soil organic matter, and Cd bioavailability. The plant growth parameters were also influenced positively by application of BC in both pot and field experiments. In field experiments, plant population and fresh biomass at different sites varied significantly. The Cd concentration in plants was lower when grown in treated soils. Moreover, there was a significant increase in soluble Si and phosphorus concentrations in plants and this had significant correlation with Cd concentration in plants.