Zinc Forms and Plant Availability in a Compost Amended Soil

Compost can be used to remediate metal-contaminatedsites because it binds metals and reduces metal uptakeby plants. A greenhouse experiment was conducted totest the effectiveness of compost to remediate Zntoxicity to plants and to determine its effect on zinc(Zn) distribution among operationally defined forms. Cecil soil (Typic kanhapludults) was amendedwith 0 to 5000 mg kg-1 Zn and biosolid compost at0, 100, and 300 tons ha-1, and then corn (Zea mays L.) was planted. After 42 days of growthplants were weighed and analyzed for Zn concentration. Soil was analyzed for Mehlich 1-extractable Zn andfractionated by a sequential extraction procedure forforms of Zn. Compost lowered soil pH while increasingCEC, exchangeable hydrogen and percent carbon. Concentrations of Mehlich 1-extractable Zn weredecreased by compost addition. Compost additionsdecreased plant Zn concentration and allowed moreplant survival with toxic levels of soil Zn. Compostamendment redistributed Zn from the water soluble andexchangeable fractions to the manganese oxide andamorphous iron oxide fractions, which shows a changein form of Zn from more plant available to less plantavailable. Biosolid compost soil amendments decreaseplant availability of Zn making it less toxic toplants even where it decreases soil pH, which wouldtend to have the opposite effect.