Acidic soil amendment with a magnesium-containing fluidized bed combustionby-product

Removal of SO2 from the emissions of coal-fired boilers produces by-product s that often consist of CaSO4, residual alkalinity, and coal ash, These by- products could be beneficial to acidic soils because of their alkalinity an d the ability of gypsum (CaSO4. 2H(2)O) to reduce Al toxicity in acidic sub soils, A 3-yr field experiment was conducted to determine the liming effica cy 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 subsurf ace soil chemistry, The FBC was mixed in the surface 10 cm of two acidic so ils (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 req uirement (LR), Soils were sampled in 10-cm increments to depths ranging fro m 20 to 110 cm, and corn (Zea mays L,) and alfalfa (Medicago sativa L,) wer e grown, Application of Mg-FBC increased alfalfa yields in all six site-yea rs, whereas it had no effect on corn grain yield in five site-years and dec reased 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 unaf fected 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 n ear 7 for 2 Sr, there was minimal effect on subjacent soil pH, Application of Mg-FBC increased surface soil concentrations of Ca, Mg, and S, which pro moted downward movement of Mg and SO4. This had different effects on subsoi l chemistry in the two soils: in the high-Ca-status Wooster subsoil, exchan geable Ca was decreased and exchangeable Al was increased, whereas in the h igh-Al-status Coshocton subsoil, exchangeable Al was decreased and exchange able Mg was increased, The Mg-FBC was an effective liming material and, bec ause of the presence of both Mg and SO4, may be more effective than gypsum in ameliorating subsoil Al phytotoxicity.