Tutorial:Soil Podzolisation

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Podzolisation
Podzolisation also involves the movement of iron oxides (or sesquioxides as they are sometimes called). In this case the movement is vertically through the soil, which leads to the formation of a distinctive podzol (UK and World Reference Soil Base), or spodosol (USDA) soil profile. They typically develop on sandy free-draining substrates with a heath or coniferous vegetation.

Podzolisation involves the formation of mor humus, an acid organic material formed by heath and coniferous trees for example. This releases soluble organic materials which percolate through the soil. As it travels through the soil this organic matter binds (complexes) with iron, silica and aluminium, which are themselves mobilized and are washed down through the profile. A pale grey, sandy, albic or eluvial horizon develops where iron, organic matter and clay are lost from the soil. The mobilised iron, aluminium, organic matter, and clay are deposited lower down the profile in a spodic or illuvial horizon, which has a dark brown or reddish colour and pellets of organic matter between sand grains.

Podzols, therefore typically have an organic surface layer (O), a pale albic horizon (Ea), and dark brown (Bh) and/or reddish spodic horizon (Bs), which may contain a thin iron pan (Bfe).

Podzols soils have acidic top soils and hence are very poor preservers of bone, shell and other calcareous materials. Podzols are important environmental indicators of soil development and change, and they may also develop in archaeological deposits where the strong horizonation can be mistaken for depositional stratigraphy.

Podzolic soils are strongly acidic, hence, bone and shell are rarely preserved.

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