Distribution of exchangeable cations and trace elements in the profiles of soils amended with coal combustion by-products

The flue gas desulfurization process employing forced oxidation technology generates an almost pure gypsum (FGD), which may substitute for mined gypsum used as a soil amendment in the southeastern United States. Under specific conditions, a mixture of FGD and fly ash (FA) may be produced by an electric power plant. A field experiment was conducted to study the effect of FGD applied both singly and as a 1:1 mixture with fly ash (AFGD) on the distribution of the exchangeable cations Ca, Mg, K, and Al and the trace elements B, As, and Pb in the profiles of soils having various textures. Lime was not applied in this study. The experiment was conducted at three different locations near Tifton, Athens, and Calhoun, Georgia. The total amount of rainfall plus irrigation at these locations during the experimental period was 1385, 1418, and 1406 mm, respectively. Soil cores were collected to a depth of 70 or 80 cm about 13 months after by-product application. FGD application increased exchangeable Ca levels in the subsoil. Exchangeable K levels were significantly decreased by FGD application only in a sandy soil. FGD promoted release of Mg from the soil sorptive complex and increased leaching of this element. Cations were transported most effectively in the profiles of a sandy soil. FA application increased plant available As in the surface layer of a sandy soil and plant available B in the zone of incorporation in the soils containing more clay, but it only partially alleviated deficiencies of this element. FA did not sufficiently supplement K and Mg losses induced by FGD application. The results of this study demonstrate that the FGD material had greater agronomic value than the mixed AFGD by-product.