2. soil orders and their features

Soil Taxonomy-
Properties of Soil
Plant & Soil Science

 Entisols are soils of recent origin. The
central concept is soils developed in
unconsolidated parent material with usually
no genetic horizons except an A horizon. All
soils that do not fit into one of the other 11
orders are Entisols. Thus, they are
characterized by great diversity, both in
environmental setting and land use.
Many Entisols are found in steep, rocky
settings. However, Entisols of large river

 Inceptisols (from Latin inceptum,
"beginning") are soils that exhibit minimal
horizon development. They are more
developed than Entisols, but still lack the
features that are characteristic of other soil
orders.
Although not found under aridic climate
regimes, Inceptisols nevertheless are widely
distributed and occur across a wide range of
ecological settings.They are often found on

 Alfisols are moderately leached soils that
have relatively high native fertility. These
soils have mainly formed under forest and
have a subsurface horizon in which clays
have accumulated. Alfisols are primarily
found in temperate humid and subhumid
regions of the world.
Alfisols occupy ~10.1% of the global ice-free
land area. In the US, they account for
~13.9% of the land area. Alfisols support

 Histosols (from Greek histos, "tissue") are
soils that are composed mainly of organic
materials. They contain at least 20-30%
organic matter by weight and are more than
40 cm thick. Bulk densities are quite low,
often less than 0.3 g cm3.
Most Histosols form in settings such as
wetlands where restricted drainage inhibits
the decomposition of plant and animal
remains, allowing these organic materials to

 Spodosols (from Greek spodos, "wood ash")
are acid soils characterized by a subsurface
accumulation of humus that is complexed
with Al and Fe. These photogenic soils
typically form in coarse-textured parent
material and have a light-colored E horizon
overlying a reddish-brown spodic horizon.
The process that forms these horizons is
known as podzolization.
Spodosols often occur under coniferous

 Andisols (from Japanese ando, "black soil")
are soils that have formed in volcanic ash or
other volcanic ejecta. They differ from those
of other orders in that they typically are
dominated by glass and short-range-order
colloidal weathering products such as
allophane, imogolite, and ferrihydrite. As a
result, Andisols have andic properties -
unique chemical and physical properties that
include high water-holding capacity and the
ability to 'fix' (and make unavailable to plants)

 Mollisols (from Latin mollis, "soft") are the
soils of grassland ecosystems. They are
characterized by a thick, dark surface
horizon. This fertile surface horizon, known
as a mollic epipedon, results from the long-
term addition of organic materials derived
from plant roots.
Mollisols primarily occur in the middle
latitudes and are extensive in prairie regions
such as the Great Plains of the US. Globally,

 Ultisols (from Latin ultimus, "last") are
strongly leached, acid forest soils with
relatively low native fertility. They are found
primarily in humid temperate and tropical
areas of the world, typically on older, stable
landscapes. Intense weathering of primary
minerals has occurred, and much Ca, Mg,
and K has been leached from these soils.
Ultisols have a subsurface horizon in which
clays have accumulated, often with strong
yellowish or reddish colors resulting from the

 Aridisols (from Latin aridus, "dry") are
CaCO3-containing soils of arid regions that
exhibit at least some subsurface horizon
development. They are characterized by
being dry most of the year and limited
leaching. Aridisols contain subsurface
horizons in which clays, calcium carbonate,
silica, salts, and/or gypsum have
accumulated. Materials such as soluble salts,
gypsum, and CaCO3 tend to be leached from
soils of moister climates.

 Vertisols (from Latin verto, "turn") are clay-
rich soils that shrink and swell with changes
in moisture content. During dry periods, the
soil volume shrinks, and deep wide cracks
form. The soil volume then expands as it
wets up. This shrink/swell action creates
serious engineering problems and generally
prevents formation of distinct, well-developed
horizons in these soils.
 Globally, Vertisols occupy ~2.4% of the ice-
free land area. In the US, they ccupy ~2.0%

 Oxisols (from French oxide, "oxide") are very
highly weathered soils that are found
primarily in the intertropical regions of the
world. These soils contain few weatherable
minerals and are often rich in Fe and Al oxide
minerals.
Oxisols occupy ~7.5% of the global ice-free
land area. In the US, they only occupy
~0.02% of the land area and are restricted to
Hawaii.

Property #1: Soil has Horizons (layers)

Property #2: Soil has Color…

Soil Property #4 - Organic Content
 Desert soils have low
organic content.
 Grasslands have high
organic content.
 The exact type of
vegetation is also
important because it
also affects pH.
 Pine needles add acid
to the soil.
 Grasses conserve
calcium and
magnesium (bases).
 Most crops like a
neutral pH.

Soil Taxonomy- 12 Soil Orders
 Soils are
classified into
into six
categories based
on diagnostic
characteristics
 The last (largest)
category will
place the soils
into one of the
12 Soil Orders.

Soil Taxonomy
1) Orders (12)
2) Suborders (54)
3) Great Groups (211)
4) Subgroups (1,100+)
5) Family (7,000+)
6) Series (a lot!)
Fine-loamy mixed, superactive, mesic Aquic Argiudolls
(This is the name of a specific soil in Soil Taxonomy)
This is the name of one
Of the 12 large categories
Mollisol - oll
Oder - root of order

Orders
 Highest and most general
of the soil classification
system (similar to the
phylum in plant
taxonomy)
 Based on conditions
under which the soil
developed
Order
oll = Mollisols

Suborders
 Grouped by similarities in
soil formation such as
wetter/dryer soil,
colder/warmer soil, etc.
Sub
Order
Order
Ud = Udic Moisture

Great Groups (not required to know)
 Based on differences
between soil horizons
Great
Group
Sub
Order
Order
Argi = Clay
accumulation

Sub Groups (not required to know)
 Describes a profile
characteristic, wetness,
sand, etc.
Great
Group
Sub
Group
Sub
Order
Order
Aquic = wet soil

Family (not required to know)
 Based on soil properties that
affect management and root
penetration, such as texture,
temperature, and depth
Great
Group
Fine-loamy, mixed, superactive, mesic Aquic Argiudolls
Family
Sub
Group
Sub
Order
OrderTexture, clay minerals, CEC, temp,

Series (not required to know)
 Named from the town or landscape
feature near where the soil was
first recognized (Eleva= Eleva, WI
or Gale for Galesville, WI .)
Great
Group
Family
Sub
Group
Sub
Order
Order

12 Soil Orders - Each Order has a diagnostic epipedon and
subsurface horizons – which could be “none”.
WEB SITE for soil orders = www.mines.uidaho.edu/pses/teach_res
 Entisol
 Inceptisol
 Andisols
 Spodosols
 Mollisols
 Alfisols
 Ultisols
 Oxisols
 Aridisols
 Vertisols
 Histosols
 Gelisols

Orders with unique parent materials:

Andisols (and)
 Volcanic ash soils.

Histosols (ist)
 Organic soils.

Vertisols (ert)
 High shrink/swell
clay soils.

Orders formed in unique
environments.

Aridisols (id)
 Arid climates.
 CaCO3 accumulation
in subsoil.

Gelisols (el)
 Colder climates.
 Permafrost layer
within 2 m of
surface.

Oxisols (ox)
 Tropics and
subtropics.
 Intensely weathered.

Entisols (ent)
 ‘Baby’ soil.
 Little to no
morphological
development.

Inceptisols (ept)
 ‘Toddler’ soils.
 Weakly developed
sub-surface
horizons.

Ultisols (ult)
 Older soils.
 “Ultimately
weathered”.
 Strongly leached.
 Sub-surface clay
accumulation.
 < 35% base sat. in
sub-soil.

Orders developed under unique
vegetative ecosystems.

Alfisols (alf)
 Forest soils.
 Usually an A-E-B
type horizon
development.
 The A horizon is
usually less than 25
cm.

Mollisols (oll)
 Grasslands soil.
 Thick, dark A
horizon.
 High % base
saturation.

Spodosols (od)
 Acid forest soils.
 Usually sandy.
 Thick, bright white E
horizon.
 Sub-surface layer of
accumulated metal-
humus complex
(Bhs and Bs
horizons).

Summary:
 3 orders with unique parent materials
(Andisols, Histisols, Vertisols).
 3 orders with unique environments
(Aridisols, Gelisols, Oxisols).
 3 orders by age of development (Entisols,
Inceptisols, Ultisols).
 3 orders by unique vegetative influence
(Alfisols, Mollisols, Spodosols).

Resources
 http://soils.usda.gov/technical/soil_orders/
 http://www.soils4teachers.org/lessons-and-
activities
 http://www.cals.uidaho.edu/soilorders/orders.
htm

2. soil orders and their features

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