Salt absorption in gypsum amended acid soils
Simultaneous retention of cation and anion in equivalent amounts with no net release of ions into solution, a process referred to as “Salt Absorption”, has been reported for kaolin group minerals. The objective of this study was to examine the extent of salt absorption in gypsum-amended acid soils from the Southeastern United States. Surface application of large quantities of gypsum (5–10 Mg ha−1) has been shown to alleviate subsoil acidity. Soil samples (0.6–0.8 m depth) representative of cultivated and virgin (woodland) sites of kaolinitic-Cecil and Wedowee (Typic Hapludults) and smectitic-Bladen (Typic Albaqult) series were incubated with varying additions of reagent-grade CaSO4.2H2O (gypsum) or phosphogypsum (PG) solutions (2g gypsum or PG L−1), which resulted in Ca2+ and SO 4 2− additions ranging from 0.48–1.50 and 0.51–1.59 cmolc kg−1 soil respectively. The composition of the soil solution, displaced following 4 h of equilibration, showed no evidence of precipitation of CaSO4. More than 94 and 89% of the Ca2+ and SO 4 2− applied, respectively, were sorbed in all the soils. The simultaneous sorption of Ca2+ and SO 4 2− in equivalent amounts with no net release of cations or anions into soil solution in these gypsum amended soils demonstrates the process of salt absorption.
Key wordsacid soil infertility aluminium toxicity calcium sorption ligand exchange phosphogypsum sulfate sorption variable charge soils
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