THE DEVELOPMENT AND MORPHOLOGY OF IRON PAN PODZOLS IN MID AND SOUTH WALES

Summary This investigation concerns a topographic sequence of iron pan podzols developed on loamy and silty parent materials in a zone of high relief and rainfall. The upper ridge flanks are occupied by a soil designated podzol with gleying; a‘Podzol’, except that the eluvial horizon is characterized by a fine prismatic structure. Each prism contains a thin, cup-shaped iron pan defining the prism core which is anaerobic because of saturation by moisture held within the overlying organic layer for a greater part of the year. Iron oxide concretions occur throughout the remainder of the profile which is kept better aerated through structural cracking within the narrow eluvial horizon. The ridge crests are occupied by the peaty gleyed podzol. Under the thicker organic layer anaerobic conditions exist throughout the eluvial horizon and the iron pan does not occur within the structural units but is confined to the base of this horizon. Iron has probably been mobilized in these soils by microbial action within an anaerobic environment. From the pollen present it appears that the earliest vegetation was high forest dominated by oak, and podzolization probably began under this cover, which was subsequently replaced by a more open forest environment with ferns, initially on the ridge crests, probably resulting from a deterioration of the climate. Gleying probably occurred under an ericaceous flora which succeeded the forest. Grassland has now extended across the ridges, except occasionally on upper ridge flanks.