Extraction of inorganic forms of translocated Al, Fe and Si from a podzol Bs horizon

A range of extractants commonly used in soil studies, both to clean up the crystalline clay minerals by dissolving poorly ordered phases, and to assist in the classification of soils, has been used to assess their efficiency in extracting inorganic forms of translocated Al, Fe and Si from a podzol Bs horizon. A 4 h extraction with ammonium oxalate pH 3 is the most efficient single procedure for these phases. It is concluded that satisfactory characterization of a podzol B horizon requires the use of two extractants: acid oxalate to assess the total amounts of Al, Fe and Si in non-crystalline weathering products, and pyrophosphate to assess the amounts in organic forms. Dithionite-citrate-bicarbonate gives a measure of total free iron oxides, but extracts only an ill-defined fraction of the allophane-imogolite complex.