Land Application of Solid Waste Compost: Impacts on Groundwater Quality and Uptake of Nutrients and Heavy Metals by Corn
Dyer, Jeffrey M.
University of Wisconsin-Stevens Point, College of Natural Resources
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Two solid waste composts and two soils were evaluated for leaching potential and plant uptake of nutrients and heavy metals. The soils included a Plano silt loam and Lapeer sandy loam. Corn growth response studies were conducted in a greenhouse pot experiment. Composts were incorporated at several rates (0- 300 T/A) based on lifetime heavy metal loading limits of each soil. Mature compost released adequate amounts of all nutrients to sustain corn growth at application rates of 80 tons/acre. Application of a relatively immature compost resulted in the immobilization of soil N and severe N deficiency in corn. Plant concentrations of Cu and Zn increased with increased application rates of composts. The heavy metals Ni, Cd, Pb, and Cr were not detected in corn grown on soils amended with either compost. The liming effect of the compost is believed to be responsible for limiting metal availability to plants. A combination of compost and inorganic fertilizer may be necessary for producing optimum crop yields. - Soil columns were used in leaching studies. The columns consisted of compost-amended surface soils underlain by 28 inches of subsoil. Columns were leached with 60 inches of water for 18 weeks. Results indicate that application of mature solid waste compost in excess of the N requirements of a crop will leach significant quantities of nitrate-N. Application of compost at rates less than 80 tons/acre did not produce nitrate-N in leachate exceeding fertilized soil background levels. Immature compost immobilized N and caused reversion of available N to the unavailable form. Nitrate-N concentrations in immature compost-amended soils were lower than levels of the control soil. Chloride, sulfate., boron, potassium, calcium, and magnesium were readily leached. The concentration of these ions in leachate increased with increasing compost application. The concentrations of Cu and Zn in leachate obtained from low application rate treatments were comparable to the controls. At high application rates these metals increased in the leachate compared to the control. The heavy metals Zn and Cu were detected in subsoil leachate at concentrations slightly higher than the control soil leachate. The metals Ni, Cr, Pb, and Cd were effectively tied up in the application zone. A combination of organic matter, increase in pH, and CEC from compost amendments may be responsible for immobilizing heavy metals. At conservative application rates of 40 tons/acre, the impact to ground water should be negligible for the compounds studied.