Use of By-product Gypsum to Alleviate Soil Acidity1
- Kenneth M. Oates and
- A. G. Caldwell2
By-product gypsum has been accumulating in large mounds in southern Louisiana for over 25 yr and little has been utilized. The objective of this study was to determine if large applications of byproduct gypsum could be used to alleviate soil acidity. A column leaching experiment was conducted using an acid subsoil amended with 5.0 gypsum equivalents of phosphogypsum, hydrofluorogypsum, or pure gypsum. In addition, several rates < 5.0 were used for the pure gypsum. Soybeans (Glycine max L.) var. ransom were then grown in a greenhouse experiment on an acid subsoil amended with 5.0 gypsum equivalents of phosphogypsum, hydrofluorogypsum, or pure gypsum. (One gypsom equivalent is defined as 4.2 cmol (+) kg−1.) Results of the column leaching experiment showed that both by- product gypsums removed more Al from the soil than did pure gypsum. They also removed Al at a faster rate than pure gypsum. Hydrofluorogypsum was the most effective. It removed 81% of the KC1-extractable Al and increased the soil pH from pH 4.9 to pH 5.3. The increased effectiveness of the by-product gypsums was shown to be due to the fluoride impurity. The Al removed by pure gypsum increased linearly as described by the regression equation of Al leached = −0.0137 + 0.276 (gypsum equivalent) [R2 = 0.99] Soybeans grown on soil amended with by-product gypsum and leached had significantly higher plant weights than soybeans grown on nonleached amended soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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