PREAMBLE
In 1992, the Environmental Protection Agency (EPA) banned the use of phosphogypsum containing more than 10 pCi 226Ra/g for application to soils (Environmental Protection Agency, 1992). This ban was based on calculations of risk assessment on the assumption that phosphogypsum would be applied to a given soil at a rate of 2700 lb/ac biennially for 100 years. As will be shown in this report, this assumption is incorrect. The Fertilizer Institute unsuccessfuily challenged the Final Rule made by the EPA who contended that this application rate truly reflected the likely usage of phosphogypsum in agriculture.
INTRODUCTION
Gypsum is used in agriculture for the following purposes:
* as an ameliorant for sodium-affected (sodic) soils which occur mainly in arid areas
and is therefore of minor interest in this report,
* as a source of the nutrients calcium (Ca) and sulfur (S) required by all crops,
* as an ameliorant for the subsoil acidity syndrome which commonly afflicts soils
in the Southeast, and
* as an ameliorant for crust and seal formation at the soil surface, a condition
commonly encountered in the sandy textured soils of the Southeast.
This report has been prepared for the Florida Institute of Phosphate Research (FIPR) with the following objectives:
* to independently assess the published experimental evidence on gypsum use in agriculture
in the Southeastern United States and in Florida in particular, and
* to compare the gypsum application rate assumed by the EPA in their calculations
to actual field practice by computing both on a lb/ac per yr basis.
To achieve these objectives, a thorough literature review was undertaken in an attempt to survey all citations so that the final outcome cannot be contested on the basis of a limited data set.
Malcolm E. Sumner. August 1995.