Impact of coal combustion product amendments on soil quality: II. Mobilization of soil organic carbon

Our previous work provided evidence that application of coal combustion pro ducts (fly ash and bed ash) at rates exceeding liming requirements may caus e considerable degradation of organic N in soils. To investigate the influe nce of such application rates on the fate of soil organic matter, we studie d the effects of different amounts (0, 20, 40, and 80 g kg(-1) soil) of bed ash and ay ash on the mobilization of organic C in soil. The studies showe d that whereas fly ash mobilized little or no organic C when applied at rat es as high as 80 g kg(-1) soil, bed ash caused substantial mobilization and loss of soil organic C when applied at or above the rate of 20 g kg(-1) so il. Chromatographic and spectroscopic methods were used to characterize the different forms of carbon mobilized in soil amended with combustion produc ts. These studies showed that various forms of organic C were mobilized by bed ash treatments such as carbohydrates, phenolic substances, humic substa nces, and amino acids. We found that the total amounts of soil organic C mo bilized by bed ash treatments were related to increased soil pH and with th e losses of C associated with increases of soluble humic substances. The lo sses of organic C from soils treated with bed ash were found to be as high as 15.5% of the total soil organic C. These studies also provided evidence for stabilization of some forms of soil organic C by Ca2+ from bed ash.