Dominant Soil Orders1

MOLLISOLS
Mollisols have a dark-colored, organic-rich surface horizon (A horizon) and are found
largely in grasslands. They occur from tropical to cold temperate, and from subhumid
to semiarid environments.
SPODOSOLS
Spodosols have moderately acidic sandy profiles with an ashywhite
upper horizon. In these soils, amorphous mixtures of
organic matter and aluminum, with or without iron, have
accumulated. They are typical of sandy soils under cool, wet
conditions under conifer and hardwood forests such as in the
boreal/cold temperate forests of Canada.
GELISOLS
Gelisols are soils that have permafrost within 100 cm of the soil
surface and/or have gelic materials within 100 cm of the soil
surface and have permafrost within 200 cm. Gelic materials are
mineral or organic soil materials that have evidence of
cryoturbation (frost churning) and/or ice segeration in the active
layer (seasonal thaw layer) and/or the upper part of the permafrost.
Occur in arctic and subarctic regions. Permafrost influences
pedogenesis through its effect on the downward movement of the
soil solution and on the soil forming processes.
HISTOSOLS
Histosols are dominantly organic. They are mostly soils that are
commonly called bogs, moors, or peats and mucks. A soil is
classified as Histosols if it does not have permafrost and is
dominated by organic soil materials.
ENTISOLS
Entisols are recent soils with little or no profile development. At
the most, have a weak organic matter surface layer (O horizon).
Include deep, uniform sandy aeolian deposits (pictured here) to
complex fluvial deposits. Some Entisols have steep, actively
eroding slopes, and others are on flood plains or glacial outwash
plains that frequently receive new deposits of alluvium.
VERTISOLS
Vertisols have a high content of expending clay and that have at
some time of the year deep wide cracks. They shrink when drying
and swell when they become wetter.
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1 Descriptions and images from–
- NRCS http://soils.usda.gov/technical/classification/orders/ (Accessed 6/13/04)
- Brady NC. RR Weil. 2008. The Nature and Properties of Soils. Prentice-Hall. Ch 3.
- Donahue, RL, R Miller, J Shickluna. 1983. Soils: An Introduction to Soils and Plant
Growth. 5th Ed. Prentice-Hall.
Other resources –
http://soils.cals.uidaho.edu/soilorders/orders.htm
http://soils.ifas.ufl.edu/faculty/grunwald/teaching/eSoilScience/soil_orders.shtml
T.Kittel 604, 211