THE VARIETY OF SOILS IN BRITAIN - The Soil - page 23

CHAPTER 2
THE VARIETY OF SOILS IN BRITAIN
The building blocks of the soil world have been described in chapter 1 as components
that, assembled in differing frameworks of solid particles and intervening pores, are
the basis of a complex physical environment. This complexity is exploited by a diverse
range of soil organisms for living space, moisture and food. In this chapter, we draw
back from considering the fine details of soil composition, and view the wide variety
of soil types that contribute to the character of different regions and localities in Bri-
tain. Many topics give comprehensive accounts of soil-forming factors, soil distribu-
tion, alternative classifications, and the application of soil science to land use and man-
agement issues, on world, national, and local scales. Here we give just an outline of
one way of looking at the formation and variety of British soils as a background to our
main theme.
The traditional 'ecological' approach to the field study of soils is to consider ver-
tical sections through this thin skin that covers most of the earth's surface. These sec-
tions are three-dimensional units, that is to say, they have both a surface area and a
depth. One particularly important contribution to this approach was that of W. L. Ku-
biena, in his topic on The Soils of Europe , mentioned in chapter 1 .
When seen in section, the character of a soil can change laterally, either abruptly
or gradually, as soil-forming conditions change. Additionally, there are changes in soil
properties and appearance as one moves downwards, from the ground surface with its
plant cover, to the unchanged parent material below. This parent material may be solid
rock, like limestone, or a relatively soft geological deposit, like London Clay, alluvium
or wind-blown sand, or a man-made deposit such as colliery waste.
In many soils it is immediately obvious that the vertically changing cross-section
of the soil unit - the 'soil profile' - consists of a sequence of distinct layers, or 'hori-
zons'. In others, although changes are taking place down the profile, they are visually
less conspicuous. Whether soil horizons are sharply distinct or not, they differ in prop-
erties such as their moisture regimes, particle size composition, handling consistency,
organic matter content and other chemical properties. The consequences of these dif-
ferences are frequently revealed as changes in colour, or in the feel of the soil when it
is handled. Although equivalent horizon thicknesses vary, their sequences down pro-
files are seen to fall into consistent arrangements that are repeated from place to place.
A common way of studying, describing and comparing soils is to dig soil profile
pits. These may need to be two or three feet deep to expose the average soil profile in