These soils result from weathering processes that leach clay
minerals and other constituents out ofthe sur and
into the subsoil, where they can hold and supply moisture and
nutrients to plants. They formed primarily under forest or
mixed vegetative cover and are productive for most crops.

ALFISOLS MAKE UP ABOUT 10% OF THE WORLD'S
ICE-FREE LAND SURFACE,

Histosols have a high content of organic matter and no perma:
frost. Most are saturated year round, but a few are freely drained.
Histosols are commonly called bogs, moors, peats, or mucks,

Histosols form in decomposed plant remains that accumulate in
water, forest litter, or moss faster than they decay. IF these soils
are drained and exposed to air, microbial decomposition is
accelerated and the soils may subside dramatically,

Histosois MAKE UP ABOUT 1%6 OF THE WoRLD'S
ICE-FREE LAND SURFACE.

Mollisols are soils that have a datk colored surface horizon
relatively high in content of organic matter. The soils are base
rich throughout and therefore are quite fertile.

Mollisols characterstically form under grass in climates that
have a moderate to pronounced seasonal moisture deficit
They are extensive soils on the steppes of Europe, Asia,
North America, and South America

Mouisots MAKE UP ABOUT 7% OF THE WORLD'S
FREE LAND SURFACE,

USDA
—_

Andisols form from weathering processes that ge

‘Asa group, Andisols tend to be highly productive soils. They
include weakly weathered soils with much voleanic glass as well

0 high precipitation,
associated with voleanic materials

ANDISOLS MAKE UP ABOUT 1% OF THE WORLD'S
ICE-FREE LAND SURFACE,

or the growth of mesophytic
tly restricts the intensity o
soll development
Is. Aridisols often
‘accumulate gypsum, salt, calcium carbona
that are easly leached from soils in more humid environments,

Aridisols are common in the deserts of the world,

Anipisots MAKE UP ABOUT 12% OF THE WORLD'S
ICE-FREE LAND SURFACE.

and other materials

Entisols are soils that show little oF no evidence of

pedogenic horizon development.
Entisols occur in areas of recently deposited parent materials or
in areas where erosion or deposition rates ate faster than the
rate of soll development; such as dunes, steep slopes, and
flood plains. They occur in many environments,

ENTISOLS MAKE UP ABOUT 16% OF THE WORLD'S
ICE-FREE LAND SURFACE,

LVE ORDERS

ly weathered soils of tropical and subtrapical
regions. They are dominated by low activity miner
‘quartz, kaolinite, and iron oxides. They tend to have
indistinct horizons,

Oxisols characteristically occur on land surfaces that have been
stable fora long time. They have low natural fertility as well as
a low capacity to retain additions of lime and fertilizer

Oxisots MAKE UP ABOUT 8% OF THE WORLD'S.
ICE-FREE LAND SURFACE,

OF

TAXONOMY

Spodosols formed from weathering processes that strip organic
matter combined with aluminum (with or without iron) from the
surface layer and deposit them in the subsoil. in undisturbed
‘areas, a gray eluvial horizon that has the color of uncoated
‘quartz overlies a reddish brown or black subsoil

Spodosols commonly occur in areas of coarse-textured
deposits under coniferous forests of humid regions.
They tend to be acid and infertile.

Srovosois MAKE UP ABOUT 4% OF THE WORLD'S
ICE-FREE LAND SURFACE.

Unisols are soils in humid areas. They formed from fairly

intense weathering and leaching processes that result in

a clay-enriched subsoil dominated by minerals, such as
quartz, kaolinite, and iron oxides.

Ulisols are typically acid soils in which most nutrients are
concentrated in the upper few inches. They have a moderately
low capacity to relain additions of lime and fertilizer.

Unmisots make uP ABOUT 8% OF THE WORLD'S
ICE-FREE LAND SURFACE,

Gelisols are soils that have permafrost near the soil surface
andor have evidence of cry
andior ice s

Gelisols are common in the higher latitudes or at
high elevations

Grusois MAKE UP ABOUT 9% OF THE WORLD'S
ICE-FREE LAND SURFACE,

Inceptisols are soils of semiarid to humid environments that
‘generally exhibit only moderate degrees of soil weathering
and development,

Inceplisols have a wide range in characteristics and occur
ina wide variety of climates,

INCEPTISOLS MAKE UP ABOUT 179% OF THE WORLD'S
ICE-FREE LAND SURFACE.

\Vertisols have a high content of expanding clay minerals. They
Undergo pronounced changes in volume with changes in
moisture, They have cracks that open and close periodically
and that show evidence of soil movement in the profile
Because they swell when wet, vertisols transmit water very
slowly and have undergone little leaching. They tend to be
fairly high in natural fertility

VeRrisots MAKE UP ABOUT 2% OF THE WORLD'S.
ICE-FREE LAND SURFACE.

Natural Resources
Conservation Service