THE VARIETY OF SOILS IN BRITAIN - The Soil - page 40

Brown Podzolic Soils are geographically important in the marginal upland zone
between the zones dominated by Brown Earths and mineral Gleys, or by peaty
moorland soils. Pedologically (in profile character), they are also transitional, fitting
between these Brown Earths and the strongly developed Podzols or Peaty Podzols
that are described below. Laboratory analyses show them to have a higher content of
'free' iron oxides than the equivalent Brown Earths, that is to say, this iron is more
readily extractable by chemical means. However, this released iron is largely retained
within the profile of Brown Podzolic Soils, as it is in the Brown Earths. The delicate
balance between vegetation, soil fauna and profile character in these transitional pod-
zolic soils is illustrated by the Scottish moorland/birch woodland cycle discussed in
chapter 7 . This balance can be disturbed by planting conifers which produce a deep,
acid mor humus. A more strongly developed podzol profile then quickly develops,
with a thin E a horizon forming beneath the mor.
In strongly developed, freely drained Podzol profiles, the iron and aluminium
are moved down the profile as organic salts (complexes). Their removal, particularly
that of the released iron, leaves a pale greyish-white mineral skeleton dominated by
the resistant silica mineral, quartz. This is the E a horizon. The transported material is
deposited in underlying B h and B s horizons, as microbial and fungal action destroys
the organic part of the transporting complex. The necessary conditions for such well-
developed Humus-Iron Podzols include very acidic, free-draining parent materials,
such as quartzite rock scree in the Highlands, or sands and gravels in low rainfall
areas. Such soils are an essential element in the ecology of English heathlands. The
typical profile in Plate 3 is from the Vale of York.
In the sequence of moorland soils, we mentioned earlier that Peaty Podzols are
relatively well drained. They nevertheless have an O horizon characteristic of wet, an-
aerobic, surface conditions due to the high rainfall in these areas. Beneath the O hori-
zon is a leached, grey-coloured E ag horizon which results partly from podzolic release
and transport of iron and aluminium, and partly from the added effects of gleying. For
this reason, such soils have been called Peaty Gley Podzols. The gleying is caused by
the sponge effect of the persistently wet O horizon above, and by impeded drainage
below. The latter is the result of a thin, hard band, or 'iron-pan', produced at the base
of the E ag horizon. Beneath the iron-pan is typically a more diffuse bright reddish-
brown B s horizon, enriched with transported iron compounds, in a moderately well-
drained position in the profile.
The last soil class in the short list summarized here is that of Organic Soils. Sub-
groups among these peaty soils are based on the nature of the underlying, or surround-
ing, geological material, which affects water chemistry. Variations also depend on the
type of vegetation that produces the peat, and on the landform in which the soils occur