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Potential Adherence of Flue Gas Desulfurization Gypsum to Forage as a Consideration for Excessive Ingestion by Ruminants
Author(s) -
Torbert H. A.,
Chaney R. L.,
Watts D. B.
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.07.0279
Subject(s) - flue gas desulfurization , gypsum , ingestion , forage , environmental science , waste management , flue gas , chemistry , agronomy , biology , engineering , materials science , metallurgy , biochemistry
Gypsum (calcium sulfate dihydrate, CaSO 4 ⋅2H 2 O) has long been used to improve soils and crop production, and its use has recently been encouraged by the USDA–NRCS for soil conservation through a new Conservation Practice Standard: Code 333. However, there is concern regarding the adverse effects of excessive direct ingestion of sulfate in gypsum by ruminants. The standard requires ruminants to be removed from grazing after application until after a rainfall, but there has been no research documenting gypsum adherence to forage or the potential for rainfall to reduce gypsum adherence. A study was established to examine the adherence and persistence of gypsum on different forage species. Two forages (bermudagrass [ Cynodon dactylon L.] and tall fescue [ Festuca arundinacea Schreb.]) were examined after gypsum applications at rates of 0, 1, and 5 Mg ha −1 . The forage was sampled immediately after application, 1 wk after application, after a 1.5‐cm rain, and after a 3.3‐cm rain. Immediately after gypsum application, more gypsum adhered to the tall fescue (27.9 g gypsum kg −1 ) compared with bermudagrass (8.6 g gypsum kg −1 ), likely due to differences in the leaf structure. This represents S concentrations of 0.16 and 0.52% for any grazing ruminants feeding exclusively on the bermudagrass and tall fescue pastures. On succeeding sampling dates, substantial amounts of gypsum persisted only on the wider‐leaved tall fescue. With tall fescue, a difference in gypsum adherence could be observed after a 1.5‐cm rain, but no significant difference was observed between the gypsum application and the control after an additional 3.3‐cm rain. Results indicate that care should be observed with grazing after gypsum application, especially on wide‐leaved forages. However, using application rates within normal agronomic beneficial use guidelines (NRCS standard 333), negative results from direct ingestion of gypsum are not likely if grazing is discontinued several weeks and until a rainfall event occurs. Core Ideas Gypsum adherence to forage may be risk for PEM for ruminants feeding exclusively on pasture. Gypsum adherence was greater on tall fescue than bermudagrass, likely due to leaf structure. No gypsum adherence was observed after a second rainfall, indicating gypsum can be washed off. Normal application rates are not likely to result in S concentrations sufficient to cause PEM.