Geoscience Reference
In-Depth Information
zons in freely drained (aerobic) conditions: O for peaty organic matter
formed under wet (anaerobic) conditions.
mineral horizons of maximum biological activity, at or near the
ground surface, in which organic matter is intimately incorpor-
ated; subdivisions include -
A
an A horizon with notably high organic matter, but not sufficient to be
an O horizon
A
h
the Ca subscript is used for horizons containing calcium carbonate, as
rock fragments or secondary concretions.
A
Ca
mineral horizons below O and/or A horizons from which iron and
aluminium and/or clay particles have been mobilized and trans-
ported to lower horizons, or out of the profile in drainage water;
subdivisions include -
E
a
horizon from which iron and aluminium have been lost.
E
mid-profile mineral horizons, modified by physical, chemical and/
or biological activity, so that they differ from horizons above, and
from the parent material below; subdivisions include -
B
B horizon notably enriched in mobilized iron and aluminium com-
pounds, released in situ or transported from above
B
s
B
h
B horizon enriched in transported humus.
parent material substantially unmodified by soil-forming pro-
cesses.
C
these are used as subscript symbols for A, E, B, and C horizons
which show strong/moderate evidence of the effects of long-term/
seasonal waterlogging.
G/g
In uncertain or transitional cases, intergrade horizon symbols (e.g. BC) are often used
in profile descriptions.
There are many variants of international and national soil classifications, which,
over the years, have been based on the work of many scientists of various national-
ities. Among current international schemes, that of the Food and Agriculture Organ-
isation of the United Nations (FAO) is in use for soil maps on continental and world
scales. The United States Department of Agriculture (USDA) 'Soil Taxonomy' is a
complex system of wide actual and potential application. It has been developed and
