Ferrihydrite in pyrophosphate extracts of podzol B horizons

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Abstract
The amount of Fe and Al extracted from soil by 0·1 M pyrophosphate (Fep, Alp) has long been used as a criterion in the designation of spodic horizons of podzols (Avery, 1973). Although Adamset al.(1980) showed that in a group of podzolic soils developed from Lower Palaeozoic sedimentary (LPS) rocks Fepwas very closely correlated with the quantities of Fe eluviated and illuviated, such evidence validating the use of pyrophosphate is not generally available. Recently there has been renewed interest in the identification of forms of Fe and Al extracted by pyrophosphate in order that greater confidence might be gained in the use of Fepand Alpin soil classification (McKeague & Schuppli, 1982).Our interest in pyrophosphate extraction was stimulated when Nto (1981) discovered that Fepwas an excellent predictor of P sorption in soils developed from LPS rocks. Indeed, the level of predictability was not improved by the inclusion, in multiple regressions, of either Fe or Al extracted by any other of the commonly used selective extractants.