Potential Adherence of Gypsum to Forage As a Consideration for Excessive Ingestion By Ruminates.

Gypsum (calcium sulfate dihydrate, CaSO4•2H2O) has long been used in agricultural to improve soils and crop production and its use has recently been encouraged by the USDA NRCS for soil conservation through a new National Conservation Practice Standard: Code 333.  However, there is concern regarding the excessive direct ingestion of gypsum by ruminants causing adverse effects.  As a result, the NRCS standard 333 specifies “Do not resume grazing until rainfall or irrigation has washed gypsum off the vegetation to address this issue.”  However, there has been no research to document 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 types.  Two different forages (bermudagrass and tall fescue) were examined following gypsum applications at 0, 1, and 5 t/ha rates.  The forage was sampled initially after sampling, one week later, after a 1.5 cm rain, and after a 3.3 cm rain.  Retained gypsum was quantitated by increase in Ca concentration in the plant sample.  Substantial amounts of gypsum were observed to adhere to the forage, but only persisted on the wider leaved tall fescue forage.  With the tall fescue, difference in gypsum adherence could be observed following a 1.5 cm rain, but no significant difference was observed between the gypsum application and the control following an additional 3.3 cm rain.  Results indicate that care should be observed with grazing following gypsum application, especially on wide leaved forages, but adhering gypsum would be removed following rain.