Availability of Sulfur in Fly Ash to Plants

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Abstract
Fly ash from a coal‐fired power plant was added to soil in variable amounts and the availability of sulfur to a variety of plant species from this source was compared to that of gypsum. The study was conducted under greenhouse conditions with a calcareous and two acid soils which were low in plant‐available sulfur.The fly ash used contained 0.4% S, all of which is extractable by NH4OAc. When mixed with a calcareous and an acid soil at rates of 1–2% by weight, the fly ash corrected a S deficiency in the soil and maximized the yield of alfalfa (Medicago sativa L.) and bermudagrass (Cynodon dactylon L.). The increase in yield (twofold to threefold in alfalfa and 40 to 70% in bermudagrass) was accompanied by an increase in the S content of the plant tops from a deficiency level (< 0.1%) to a sufficiency level (≥ 0.2%). The availability of fly ash‐S and gypsum (CaSO4·2H2O)‐S was compared by the addition of equal amounts of S from the two sources (25‐, 50‐, and 100‐mg S/kg soil) to an acid soil. Yield and S content of turnip (Brassica rapa L.) and white clover (Trifolium repens L.) were equally improved, demonstrating that the availability of fly ash derived‐S is equivalent to that of gypsum‐S.

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