Zinc forms and plant availability in a compost amended soil

Compost can be used to remediate metal-contaminated sites because it binds metals and reduces metal uptake by plants. A greenhouse experiment was cond ucted to test the effectiveness of compost to remediate Zn toxicity to plan ts and to determine its effect on zinc (Zn) distribution among operationall y defined forms. Cecil soil (Typic kanhapludults) was amended with 0 to 500 0 mg kg(-1) Zn and biosolid compost at 0, 100, and 300 tons ha(-1), and the n corn (Zea mays L.) was planted. After 42 days of growth plants were weigh ed and analyzed for Zn concentration. Soil was analyzed for Mehlich 1-extra ctable Zn and fractionated by a sequential extraction procedure for forms o f Zn. Compost lowered soil pH while increasing CEC, exchangeable hydrogen a nd percent carbon. Concentrations of Mehlich 1-extractable Zn were decrease d by compost addition. Compost additions decreased plant Zn concentration a nd allowed more plant survival with toxic levels of soil Zn. Compost amendm ent redistributed Zn from the water soluble and exchangeable fractions to t he manganese oxide and amorphous iron oxide fractions, which shows a change in form of Zn from more plant available to less plant available. Biosolid compost soil amendments decrease plant availability of Zn making it less to xic to plants even where it decreases soil pH, which would tend to have the opposite effect.