SOLUBILITY AND PLANT UPTAKE OF METALS WITH AND WITHOUT LIMING OF SLUDGE-AMENDED SOILS

Excessive applications of sewage sludge and pig manure have led to the accumulation of potentially toxic elements in soils. The objective of this study was to examine the NaNO3 extractability of Cu, Zn, and Cd with time and in relation to soil pH and soil organic matter content a nd to investigate the concentrations of these metals in pea (Pisum arv ense L.) as a result of liming. The field study was conducted on an or thic luvisol with pig manure and sewage sludge application rates of 5 t dry organic matter ha(-1) yr(-1) from 1976 to 1984, After 1984, all field plots were equally treated with mineral fertilizers and in 1991, lime was added to half of each plot, The soil pH decreased in all unl imed treatments about half a unit from 1985 to 1991, Concurrently, the Zn and Cd concentrations extractable with 0.1 M NaNO3 increased as we ll as the Cd concentrations in field pea. Liming raised the soil pH by approximately one unit to 6.4 and 6.9 in pig manure-and sewage sludge -treated plots, respectively and resulted in decreasing concentrations of Cu, Zn, and Cd in seeds and crop residues of field pea. The result s suggested that plant uptake and solubility of Zn, Cu, and Cd can con tinue to be higher in sewage sludge-and pig manure-treated soils than in control plots during a 10-yr period after the applications were cea sed. Liming most effectively reduces the solubility and the plant upta ke of Zn and Cd.