Long-term effects of gypsiferous coal combustion ash applied at disposal levels on soil chemical properties

Currently, there is renewed interest in the agricultural utilization of coal combustion byproducts. Field sites where high rates (112 Mg ha^–1) of high gypsum coal combustion spent bed ashes were surface applied in 1980 within fruit tree orchard rows were identified and sampled with depth. The objective of this study was to examine the effects on long-term exposure/leaching of these materials on soil profile chemical properties. When applied, the material had an aqueous pH of 12.5 and consisted of about 52% calcium sulfate, 33% calcium oxide and 15% coal ash residues. Eleven years after ash application, soil pH is significantly higher in the top 66 cm of the treated sites compared to unamended sites. This has been accompanied by increases in extractable and total calcium and total boron and sulfur with a concomitant reduction in extractable magnesium. Remaining pieces of the applied spent bed material are composed primarily of calcite and quartz with some gypsum associated with large pieces.