EVALUATION OF COAL COMBUSTION BY-PRODUCTS AS SOIL LIMING MATERIALS - THEIR INFLUENCE ON SOIL-PH AND ENZYME-ACTIVITIES

There is considerable interest in the use of coal combustion byproduct s as soil liming materials in agricultural production, but there is co ncern that such use may be detrimental to the quality of agricultural soils. To evaluate these byproducts as liming materials and address is sues related to soil quality, we compared the influence of different a mounts of four combustion byproducts [fly ash and bed ash from a fluid ized bed combustion furnace, lime-injected multistage burner residue, and spray dryer residue] and CaCO3 on soil pH and activities of urease , phosphatase, arylsulfatase, and dehydrogenase in an acidic soil. Stu dies comparing the influence of the combustion byproducts and CaCO3 on soil pH showed that on a weight basis of application, substantial dif ferences were observed in the ability of these materials to influence soil pH but that such differences decreased markedly after the data we re transformed to a CaCO3 equivalent basis of application. Analysis of covariance for these transformed data indicated that whereas the limi ng abilities of fly ash and CaCO3 were not significantly different whe n compared on the CaCO3 equivalent basis, those of bed ash, multistage burner residue, and spray dryer residue were less than that of CaCO3. Studies comparing the influence of the byproducts and CaCO3 on soil e nzyme activities showed that the effect of these liming materials on t he enzyme activities studied was largely due to their influence on soi l pH. The relationships obtained between soil pH and enzyme activities in soil amended with the liming materials generally demonstrated the marked similarities in the influence of the combustion byproducts and CaCO3 on these activities when observed within the domain of soil pH. These studies showed that the combustion byproducts tested functioned as soil liming materials in a manner similar to that of CaCO3 and seem ed to have little adverse effect on soil quality.