Amelioration of Soil Acidity with Class-C Fly Ash: A Field Study

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Coal combustion products (CCP) include fly ash and bottom ash and are generated nationally at rates of 108 Mg per year. Fly ashes (FA) comprise the majority of CCP production, and can possess widely-variable physicochemical properties. Current consumption/utilization of FA in the US does not approach production levels, and results in FA stockpiling. Class-C fly ash is generated from combustion of sub-bituminous and lignite coal products. This class of FA often possesses an alkaline pH, resulting from calcium, magnesium, and potassium oxide inclusions. Some Class-C FA have been reported to contain as much as 60% calcium carbonate equivalency (CCE), prompting investigations of FA as a lime substitute in agricultural/horticultural applications. Furthermore, FA often possesses small concentrations of exchangeable micronutrients. Thus, considering availability of Class-C FA, its potential beneficial use as a liming agent, and the expansive area of low-to-medium maintenance turfgrass systems currently afflicted by suboptimal soil pH levels; our objective was to evaluate the acid-neutralizing efficacy of a Class-C FA when substituted for pulverized limestone (PL) in field application. This study was conducted on a severely-acidic bermudagrass (Cynodon spp. L.) rough of a Georgia golf course during 2001 and 2002. Following material characterization, CaCO3 equivalent was applied at a prescribed rate of 3.8 Mg CaCO3 ha−1, using either PL or Georgia-produced FA (CCE = 45.5%). Soil samples collected one year following showed FA to have neutralized significantly greater acidity in the upper 8 cm of soil than the PL. Furthermore, exchangeable P, Mg, and Zn levels in the FA-treated 0–8 cm of soil exceeded levels observed in the PL-treated or control plots. Due to the disparity in CCE, requisite FA application greatly exceeded that of PL, reducing economic advantage of FA-substitution. However, in locations where Class-C FA is plentiful, high-grade PL is costly, and soil pH suboptimal for important crops; results of this study indicate soil liming with Class-C FA to be a beneficial use of this CCP. Comprehensive characterization of CCP and proper application rate (not exceeding agronomic requirements) are essential components of beneficial use.