USE OF FLY-ASH IN REDUCING HEAVY-METAL TOXICITY TO PLANTS

An alkaline fly ash was used to reduce the metal toxicity of contamina ted soil through immobilization of heavy metals. Pot culture studies w ere carried out with maize (Zea mays) crop grown in acidic sandy loam (pH 4.9) and calcareous silty clay (pH 7.9) soils treated with known c oncentrations of heavy metals (viz. cadmium, copper, nickel and zinc). Fly ash was mixed in metal-treated soil at the rate of 0%, 2%, 5%, 10 %, 15%, 20%. The possible variation in metal toxicity to the plants du e to fly ash treatment was ascertained through changes in growth patte rns. Application of 2% and 5% of fly ash to the calcareous soil shows better growth response as compared to control soil. However, when the fly ash application exceeds 5%, the crop growth was significantly redu ced. On the contrary, acidic soil shows positive response with a fly a sh addition up to 20% but the resultant crop growth was lesser as comp ared to growth of plants in the virgin soil (i.e. soil as such, withou t fly ash and metal treatment). Fly ash addition effectively raised th e pH of acidic soil and thus helped to reduce the metal solubility and availability to plants.