Response of Corn to Zinc and Chromium in Municipal Wastes Applied to Soil1
- J. J. Mortvedt and
- P. M. Giordano2
Two coarsely ground air-dried municipal sewage sludges and a garbage compost were mixed with Hartsells fsl (limed to pH 5.5) rates of 15, 75, or 300 g/3 kg of soil in two greenhouse pot experiments. Fine ZnSO4 and Na2Cr2O7 were each mixed with soil limed to pH 5.5 to 7.0 at rates up to 1,400 ppm of Zn and 320 ppm of Cr, equivalent to rates applied in the organic wastes. Three successive crops of corn (Zea mays L.) were planted 0, 7, and 18 months after waste application.
Corn forage yields were increased only in Crops 1 and 3 by compost applications but were not affected by sludge applications. Concentrations of Zn in the corn forage increased with application rate and Zn content of the three waste products. In contrast, Cr concentrations in the corn were not affected by the 0.05% to 1.36% Cr in the wastes. Concentrations of both Zn and Cr in the corn forage were much higher from ZnSO4 and Na2Cr2O7 from each waste at similar Zn and Cr rates and soil pH. Levels of 0.5N HCl-extractable Zn and Cr in the soil after each harvest increased with application rate of Zn and Cr in each organic waste and inorganic salt, but were not proportional to plant concentrations.
Trivalent Cr as Cr2(SO4)3 was less toxic to corn than hexavalent Cr as Na2Cr2O7 at a rate of 80 ppm of Cr, while both sources were very toxic at 320 ppm. Toxicity resulted from ZnSO4 in pH 5.5 soil at 240 ppm Zn and at 960 ppm in soil above pH 6.5. Results of these experiments suggest that Zn and Cr contained in municipal wastes applied at high rates are not toxic to corn even after relatively long periods in the soil. Reduced plant uptake of these heavy metals in organic waste was not due entirely to their liming effect on the soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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