Acidic Soil Amendment with a Magnesium-Containing Fluidized Bed Combustion By-Product

Removal of SO₂ from the emissions of coal-fired boilers produces by-products that often consist of CaSO₄, residual alkalinity, and coalash. These by-products could be beneficial to acidic soils because of their alkalinity and the ability of gypsum (CaSO₄.2H₂O) to reduce AI toxicity in acidic subsoils. A 3-yr field experiment was conducted to determine the liming efficacy of a fluidized bed combustion boiler by-product (FBC) that contained 129 g Mg kg⁻¹ as CaMg(CO₃)₂ and MgO and its effects on surface and subsurface soil chemistry. The FBC was mixed in the surface 10 cm of two acidic soils (Wooster silt loam, an Oxyaquic Fragiudalf, and Coshocton silt loam, an Aquultic Hapludalf) at rates of 0,0.5,1, and 2 times each soil's lime requirement (LR). Soils were sampled in 10-cm increments to depths ranging from 20 to 110 cm, and corn (Zea mays L.) and alfalfa (Medicago sativa L.) were grown. Application of Mg-FBC increased alfalfa yields in all six site-years, whereas it had no effect on corn grain yield in five site-years and decreased grain yield in one site-year. Plant tissue concentrations of Mg, S, and Mo were increased by Mg-FBC, while most trace elements were either unaffected or decreased. Application of Mg-FBC at one or two times LR increased surface soil pH to near 7 within 1 wk. Although surface soil pH remained near 7 for 2 yr, there was minimal effect on subjacent soil pH. Application of Mg-FBC increased surface soil concentrations of Ca, Mg, and S, which promoted downward movement of Mg and SO₄. This had different effects on subsoil chemistry in the two soils: in the high-Ca-status Wooster subsoil, exchangeable Ca was decreased and exchangeable Al was increased, whereas in the high-Al-status Coshocton subsoil, exchangeable Al was decreased and exchangeable Mg was increased. The Mg-FBC was an effective liming material and, because of the presence of both Mg and SO₄, may be more effective than gypsum in ameliorating subsoil Al phytotoxicity. Salaries and research support provided by state and federal funds appropriated to the OARDC, Ohio State Univ. Manuscript no. 34-98.