A summary of research findings by the University of Georgia Soil Science research team into alternative agronomic uses of CCPs. |
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Gypsum, or calcium sulfate, is a powdery, whitish/grayish mineral found naturally in rocks and soils, and produced synthetically by coal-burning power plants when sulfur dioxide is removed from stack gases using forced oxidation scrubber technology (“flue-gas desulfurization gypsum”, or FDG). Up to 3 million mt/yr are produced annually in the U.S., with that amount likely to increase as emissions reductions are mandated by regulatory agencies. Some limited fraction of this production is used in wallboard manufacture, as a cement additive, and as structural fill. Most is stored on-site. | ||||||
| In the western U.S. gypsum is used to amend soils high in sodium, thereby improving soil physical properties. In the eastern U.S. gypsum is occasionally used at low rates (50 lbs/ac) as a S fertilizer amendment, but its high Ca content suggests that at high application rates (tons/acre) it may be able to offset the negative effects of low Ca and high Al that are thought to inhibit deep root growth on soils of the Southeastern U.S. Here the soils are highly weathered, with subsoils that lack Ca and have accumulated Al (acidity) over time. Gypsum is soluble enough (2 g/L, or 25 mM) to love into the subsoil over a period of 1-2 years and potentially stimulate deeper rooting, and hence more nutrient and water uptake from deeper in the soil. Gypsum also can be used at rates of 1-2 t/ac as a flocculating agent applied to topsoils in the Southeast. The salt released by the gypsum keeps the fine soil particles aggregated, which reduces the amount of runoff and erosion caused by rainfall. Contaminant levels are generally low in FDG; some B may be present, which can cause short-term plant toxicity, but is not a regulated pollutant. Thus it typically can be used without concern for environmental contamination, even at high rates.
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