Geoscience Reference
In-Depth Information
T A B L E 1 1 . 1
Well-Developed Mineral SoilsT
Order Name
Derivation
Characteristics
Alisols
Nonsense syllable
Soils with high-base-content B horizon rich in eluviated clay. Found from low to
subarctic latitudes.
Aridisols
Soils in dry climates that are low in organic matter and frequently have subsurface
horizons rich in calcium carbonate or soluble salts.
Latin:
aridus
= dry
Mollisols
Soils in semi-arid/subhumid grasslands in midlatitudes that have humus-rich A hori-
zon and a B horizon that has a high base status.
Latin:
mollis
= soft
Oxisols
Highly weathered soils in tropical environments that have low base status and sub-
surface horizon that has a high oxide concentration.
French:
oxide
= oxide
Ultisols
Highly weathered soils in tropical and subtropical environments that have low base
content and a subsurface horizon rich in eluviated clay.
Latin:
ultimus
= last
Spodosols
Soils in cool, moist environments that have a B horizon rich in eluviated sesquiox-
ides.
Greek:
spodos
= wood ashes
Vertisols
Tropical and subtropical soils with high base status that contain an abundant amount
of expandable clay that swells when wet and shrinks when dry.
Latin:
verto
= turn
Organic Soils
Gelisols
Largely organic soils that form in extremely cold environments where permafrost is
thick. Due to repeated freezing and thawing, soil horizons and surface expression
are chaotic.
Latin:
gelare
= freeze
Histosols
Very dark soils consisting mostly of organic matter. Typically found in cool/moist
environments where organic decomposition is slow.
Greek:
histos
= tissue
Weakly Developed Soils
Andisols
Spanish: Andes
Weakly developed soils formed within glassy volcanic sediments ejected by active
volcanoes.
Entisols
Latin:
recens
-fresh
Horizonless soils usually formed within recently deposited sediments.
Inceptisols
Soils with poorly developed horizons, but which may evolve further.
Latin:
inceptum
= beginning
extent, consider that 50 suborders and 180,000 soil series are
recognized in the United States. It is well beyond the scope
of this text to describe each of the soil series that has been
identified, but we will outline the basic characteristics of the
12 soil orders. This will provide a good overview of how
soils differ and how pedogenic processes and factors affect
soil development.
the soil-forming factors: (1) climate, (2) organisms, (3) relief,
(4) parent material, and (5) time. Note that two of these fac-
tors, climate and organisms, are distinctly environmental in
nature. In other words, they reflect the specific climate and
vegetation relationships in any given place or region. Giv-
en this close correlation, it should not surprise you that the
global distribution of soil orders reflects these environmental
factors and thus builds directly on the previous two chapters.
Figure 11.22 shows the geographic distribution of soil orders
on Earth. Notice the similarity of the patterns on this map
and the global climate and vegetation maps seen earlier (see
Figures 9.2 and 10.6, respectively). As you work your way
through this discussion, try to keep these geographic patterns
in mind.
The Twelve Soil Orders
This portion of the soils discussion focuses on the 12 soil
orders that occur within the soil taxonomy classification sys-
tem. These soils reflect the maximum development that occurs
in these orders in association with various combinations of
