Sewage Sludge Application to Calcareous Strip‐Mine Spoil: II. Effect on Spoil and Corn Cadmium, Copper, Nickel, and Zinc

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Abstract
Metal concentrations in calcareous strip‐mine spoil and corn tissue (Zea mays L.) were examined in a long‐term field experiment using anaerobically digested sewage sludge. A total of 258 dry Mg ha−1 of sludge were applied to the highest sludge treatment from 1973 to 1977. Sewage sludge significantly increased the amounts of 0.1M HCl‐extractable Cd, Cu, Ni, and Zn in the spoil (0–15 cm). Spoil pH, 7.8, was not significantly affected by sludge applications, but yearly pH varied significantly.Cadmium and zinc concentrations in leaves and grain were significantly increased each year by sludge applications. In 1977, 28.7 µg Cd g−1 and 200 µg Zn g−1 were observed in leaves from the highest sludge treatment. Grain Ni concentrations were significantly increased after application of 258 Mg ha−1 of sludge. Significant (P ≤0.01) increases were observed for the total plant uptake of Cd and Zn from 1974 to 1977 and Ni in 1977. The order of metal enrichment for corn was Cd > Zn > Ni > Cu.Regression analyses showed that for Cd, Ni, and Zn the cumulative application in sludge and the 0.1M HCl‐extractable amounts from spoil were the most significant variables relating to the additive increases of these metals in corn tissue. The spoil mineral composition and pH appeared to be important in determining why Cd, Ni, and Zn availability did not decrease rapidly with time.