Geoscience Reference
In-Depth Information
refined over many years, in successive 'approximations', to its present form, which
uses its own, self-contained and specialized, terminology. You will sometimes see
class names from these systems cross-referenced in papers describing soils by nation-
al systems.
In Britain, there are currently two 'official' systems in use which, unfortunately,
differ in their terminology, and in the application of similar technical terms. Both,
however, are intended to be fully comprehensive for their respective areas. They have
been established by the Soil Survey of England and Wales (now the Soil Survey and
Land Research Centre, based at Silsoe, Bedfordshire) and the Soil Survey of Scotland
(of the Macaulay Land Use Research Institute, Aberdeen). The 1:250,000 scale maps
and accompanying 'Bulletins' of the former, which give a complete cover of England
and Wales, use a classification that starts with 10 'major soil groups'. These are di-
vided into 34 'groups', 67 'sub-groups', and finally some 700 'soil series'. These last
are soils of a particular sub-group formed from a specified parent material, defined by
soil texture (particle size composition) and source rock types. The 296 'soil associ-
ation' map units at the regional scale are complexes of named dominant and subordin-
ate series. The criteria for differentiating these series, and an index to them, requires
a publication of some 150 pages.
The Scottish 1:250,000 scale maps and accompanying 'Handbooks' begin with
5 'soil divisions' which are progressively split into 12 'major soil groups', 36 'major
soil sub-groups', 110 'soil associations' and 580 mapping units. These mapping units
are comparable in concept to 'soil associations', as the term is used in the England
and Wales survey, but they cannot be directly related to each other.
Variations on these traditional classifications have been developed over the past
60 years and can cause confusion. Some approaches use simple schemes, others in-
volve much more detail. The former have the advantage of presenting a broad pic-
ture but the disadvantage that a high proportion of real-world soils fall between their
classes. One such classification, derived from existing conventions, was suggested by
one of us (D.F.B.) elsewhere as an appropriate baseline for broad ecological/soil cor-
relations. It used seven major soil groups divided into 32 sub-groups, but for present
purposes only 12 of these are emphasized here as giving a suitable background for ap-
preciating soil diversity in relation to biological themes. Some soil names are self-ex-
planatory in English while others (rendzina, gley, podzol) are derived from languages
of other countries, particularly Russia, where their distinct characters were first re-
cognized and described. Their typical horizon sequences are listed first, followed by
a brief outline of the nature of each soil. Conventionally, and throughout this topic,
these soil names are treated as proper nouns, i.e. with capital letters.
