Effects of drying and wetting on extractable aluminum in strongly acid soils and in aluminum-saturated clays

A number of field-moist strongly acid soils, NaObr-treated soils, and Al-saturated clays were subjected to drying and wetting treatments in the laboratory. Oven drying of samples resulted in decreases in extractable Al and increases in extractable H from field-moist soils containing more than 12 mequiv./100 g exchange acidity and from Al-saturated clays, and wetting the samples resulted in the reverse. However, when field-moist soil samples containing less than 7 mequiv./100 g exchange acidity were oven dried, both the extractable Al and extractable H tended to increase. Removing organic matter with NaOBr from a soil sample low in exchange acidity resulted in a change from an increase to a decrease in extractable Al upon oven drying. In all cases, the extractable Al and extractable H contents fluctuated cyclically with repeated drying and wetting. The cause for the observed changes was attributed to Al hydrolysis, with additional influence from soil acidity buffering, Al interlayer formation, and inorganic and organic matter dissolution.