Geoscience Reference
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original objective that had been mainly the creation of linkages between
national classifications was half-abandoned (Yaalon 1995). A. Ruellan of
France, O.C. Spaargaren of the Netherlands and J. Decker of Belgium
formed the first sequence of leaders of the group that developed the
WRB.
We shall examine the 2006 version of the WRB. It proposes organization
of soils into two taxonomic levels.
The first and main level is '
Reference Soil Groups
' (
RSG
s), numbering
32. Their identification is made on the basis of three kinds of indicators.
First to be considered is the presence or absence of 39
diagnostic
horizons
. For example, a Histosol has a diagnostic
Histic
horizon or
a diagnostic
Folic
horizon. In certain cases,
diagnostic properties
, the
list currently numbering 14 items, are used. These properties are
introduced in addition to the diagnostic horizons because they do not
strictly pertain to a specific diagnostic horizon. For example, an '
abrupt
textural change
' or occurrence of '
albeluvic tonguing
' (degraded tongues
of a bleached and depleted horizon penetrating a horizon enriched in
clay) are properties that, in each case, involve two adjacent horizons.
In the third place, if needed, we can refer to the presence of
diagnostic
materials
. These, numbering 12, stamp on the soil its essential properties
when pedogenetic evolution did not have the time to get involved, and
therefore when the idea of diagnostic horizon is not operational. For
example, a '
fluvic material
' is enough to identify a Fluvisol (alluvial soil),
in the absence if not of all diagnostic horizons, at least of any diagnostic
horizon indicating marked genetic evolution.
The second level, qualified without greater precision at the
lower
level
or the
second level
, permits characterization of the soils one by
one by attaching a
qualifier
or
formative element
to the name of a
RSG
.
This qualifier is placed before the name if it refines the classification:
orthotype versus intergrade to another type. For example, an alluvial
bog soil is a
Histic Fluvisol
, whereas a true peat will directly qualify as
Histosol
. On the contrary, the qualifier is placed after the name of
RSG
if it
only defines a detail. For example, a silty alluvial soil is
Fluvisol Siltic
.
Altogether, the qualifiers (prefixes + suffixes) number 157. But some
of them could be themselves flanked by a prefix that defines them
more precisely, which augments the number of possibilities, for example
Glossalbic
in addition to
Albic
and
Thaptovitric
(
thapto
indicating buried)
in addition to
Vitric
. The most used prefixes, the
Specifiers
, are ten in
number and form a separate list, for example
Endo
,
Epi
,
Hyper
…
Principle of use
