Effect of Biogas Slurry-Modified Biochar on Cd Immobilization, Uptake, Translocation, and the Bioavailability of N, P, and K in Soil

Abstract The purpose of this study was to assess the capability of four biochar-based fertilizers to remediate Cd-contaminated soils and their effect on plant nutrition.First, agricultural soil used for cacao production was collected. Then, soil was amended with four types of biochar and four biochar-based fertilizers. Subsequently, cucumber seedlings were planted in the amended soils to evaluate the bioavailability of Cd, N, P, and K. To explore the possible mechanisms involved in soil remediation, geochemical fractionation was applied.Compared to the control, plants treated with raw biochar and biochar-based fertilizers exhibited a reduction in Cd concentration of approximately 0.8- and 0.5-fold, respectively. An effect on the distribution of Cd in roots and shoots was observed. The application of biochar-based fertilizers increased Cd accumulation in the roots while reducing Cd accumulation in the shoots. This was significantly correlated with the increased concentration of bioavailable P in the soil. The reduction in Cd bioavailability was significantly correlated with increases in pH, organic matter, and cation exchange capacity. The geochemical fractions suggest that Cd immobilization is influenced by both indirect mechanisms and direct mechanisms. Increases in the F4 fraction, associated with Cd retention due to organic matter, are predominant in soils treated with biochar-based fertilizers. The bioassay results demonstrated a positive effect on N, P, and K uptake by cucumber plants when raw biochar and biochar-based fertilizers were applied.Overall, this study provides novel insights, suggesting the potential use of biochar-based fertilizers for the remediation of agricultural soils.