Reducing soluble lead and cadmium in contaminated soils using dairy cattle waste based vermicompost

Continuous use of synthetic fertilizer can lead to the accumulation of heavy metals in the soil. The use of organic amendment can reduce the solubility of heavy metals such as Pb and Cd in soil. The experiment was undertaken to determine the decline of soluble Pb and Cd in polluted soils treated with dairy cattle waste-based vermicompost. The study used two soil samples; Inceptisols collected from Air Duku Village and Entisol from Beringin Raya Village, Bengkulu, Indonesia. Entisols and Inceptisols contained 2.0 and 0.4 mg kg-1 soluble Pb and 0.7 and 0.8 mg kg-1soluble Cd, respectively. The samples were pretreated with either 100 ppm Pb or Cd. Vermicompost was applied at the rate of 0, 10, 20, and 30 Mg ha-1 on samples of Inceptisols and Entisol, arranged in Completely Randomized Design (CRD). The mixture was incubated for eight weeks. After the incubation ended, the soil sample was analyzed for soluble Pb and Cd using DTPA extraction before detection using Atomic Absorption Spectroscopy. The study resulted that the soluble Pb and Cd significantly reduced with vermicompost treatment, being the lowest was at the rate of 30 Mg ha-1. Furthermore, the decreased soluble Pb and Cd was more substantial in Inceptisols than Entisols. Soluble Pb in both soils was lower than Cd, suggesting a higher retention affinity of the former. This study summarizes that vermicompost at the rate of 30 Mg ha-1 effectively immobilizes Pb and Cd in contaminated soils.