Geoscience Reference
In-Depth Information
Table 5-1.
Original ten United States soil orders and a
description of their formative elements. Based on Soil
Survey Staff (1975, Table 8, p. 87).
rei ned considerably. Such issues are now under
the purview of the National Technical Committee
for Hydric Soils, which was originally charged
with i nalizing a dei nition of hydric soils and
creating a list of hydric soils in the early 1980s
and continues to serve i ve major functions with
regard to wet-hydric soils (National Technical
Committee for Hydric Soils 2010):
Formative
element
Soil order
Derivation
Pronunciation
Alfi sols
Alf
Meaningless
Pedalfer
Aridisols
Id
Latin - aridus,
dry
Arid
Entisols
Ent
Meaningless
Recent
Histosols
Ist
Greek - histos,
tissue
Histology
• Provide technical leadership.
• Update and distribute a national list of hydric
soils.
• Rei ne and maintain “Field Indicators of
Hydric Soils.”
• Communicate and respond to public com-
ments regarding hydric soil dei nitions.
• Conduct research regarding data necessary
to better dei ne hydric soils.
Inceptisols Ept
Latin -
inceptum,
beginning
Inception
Mollisols
Oll
Latin - mollis,
soft
Mollify
Oxisols
Ox
French - oxide
Oxide
Spodosols
Od
Greek - spodos,
wood ash
Odd
Ultisols
Ult
Latin - ultimus,
last
Ultimate
The best and most up-to-date source for infor-
mation about hydric soils and hydric-soil dei ni-
tions in the United States is the USDA/NRCS
hydric soils website, which includes dei nitions
of terms, criteria, technical notes, lists of i eld
indicators, and state and national lists of hydric
soils (see http://soils.usda.gov/use/hydric/).
The Canadian system of soil taxonomy follows
that of the United States closely, although with
some distinct differences in hierarchical struc-
ture and i eld criteria; a greater emphasis is
placed on the uppermost soil horizon (Soil Clas-
sii cation Working Group 1998). The Organic
order includes soils that develop in poorly
drained settings that are saturated for prolonged
periods. Organic soils are separated into four
great groups: Fibrisol, Mesisol, Humisol, and
Folisol. Fibrisols are composed of relatively
undecomposed plant tissues (peat), whereas
Humisols represent advanced decomposition
(muck). Mesisols are intermediate; all three great
groups are hydric soils. The Folisols, in contrast,
form in upland forest settings rather than
wetlands.
At present, various other national soil clas-
sii cation systems differ considerably from the
U.S. and Canadian approach, and knowledge of
soils is far from complete around the world,
“therefore it is not possible to develop an
Vertisols
Ert
Latin - verto,
turn
Invert
Figure 5-8.
Shallow ground water,
∼
20 cm deep, soaks
upward through clayey silt to evaporate at the surface
of this saline mud l at in western Kansas, United States.
Note dark masses of organic-rich sediment just below
the surface. This soil displays a strong rotten-egg odor.
Comb is
∼
5 inches (12.5 cm) long; photo by J.S. Aber.
was to create a hydric soil classii cation that cor-
related wet soils with hydrophytic vegetation.
The dei nition of what hydric soils are, how long
they take to form, and how long they must
be saturated to be called hydric soils has been
