The document provides information on the 12 soil orders classified in Soil Taxonomy. It summarizes the key properties and global distribution of each soil order in 1-2 sentences. The soil orders discussed are Entisols, Inceptisols, Mollisols, Alfisols, Ultisols, Oxisols, Vertisols, Andisols, Histosols, Spodosols, Aridisols, and Gelisols. For each order, the text highlights characteristic features, climate and parent material associations, and examples of their occurrence around the world.

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1. ENTISOLS
Soil Taxonomy Classification Sytem
(‐ent)
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Major soil property: featureless soil bodies Climate:
‐ may form in a variety of climates
Diagnostic horizons: typically absent, albic
Epipedon: ochric (light color due to limited
Examples
accumulation of OM)
1. an arid or pergelic (cold) climate may limit the amount of
Characteristic: little or no evidence of soil p
soil development to inhibit the formation of other soil
development
d l orders
The Entisols are recent soils occuring on flood‐plains Pergelic = mean annual soil temperature is between‐4°C to ‐10°C
of large rivers or on other recent deposits. The recent
2. A pronounced saturation of the soil profile or even
deposits generally show stratification.
submergence for long enough periods inhibit soil
development
Parent Material:
1. Entisols are on land surfaces that are very young
(alluvium, colluvium, mudflows)
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Colluvium Parent Material:
2. extremely hard rocks (e.g. Orthents), or disturbed
material (e.g. mined land, highly compacted soils, toxic
material).
3. They also occur on deep bodies of water and glaciers
which are transitions between 'soils' and 'not soils .
soils not soils'
Effect of gravity
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Parent Material:
4. They are also typical of the
shifting sands of the Sahara
Desert and Saudi Arabia.
Parent Material:
5. In serpentine barrens (Serpentinite rocks), Entisols may
be associated with bedrock outcrops.
6. Entisols may be also associated with salt flats.
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5. Million years ago (Ma)
Era
eon
Epoch
Period
Supereon
c.4570 Cryptic Era
c.4150 Basin Groups
c.3920 Nectarian
Hadean
c.3850 Lower Imbrian
3800 Eoarchean
3600 Paleoarchean
3200 Mesoarchean
Archean
2800 Neoarchean
2500 Siderian
2300 Rhyacian
Paleoproterozoic
Precambrian
2050 Orosirian
1800 Statherian
1600 Calymmian
1400 Ectasian Mesoproterozoic
Proterozoic
1200 Stenian
1000 Tonian
850 Cryogenian Neoproterozoic
630 +5/-30 Ediacaran
542.0 ± 1.0 Lo
ower/Early
513.0 ± 2.0 Middle
Cambrian
Upp
per/Late or
501.0 ± 2.0 - 496.0 ± 2.0
Furongian
488.3 ± 1.7 - 478.6 ± 1.7 wer/Early*
Low
471.8 ± 1.6 - 468.1 ± 1.6 Middle* Ordovician*
460.9 ± 1.6 - 445.6 ± 1.5 Up
pper/Late*
443.7 ± 1.5 - 436.0 ± 1.9 Lo
ower/Early
428.2 ± 2.3 - 426.2 ± 2.4 W
Wenlock
Silurian
422.9 ± 2.5 - 421.3 ± 2.6 Up
pper/Late
418.7 ± 2.7 Pridoli
416.0 ± 2.8 - 374.5 ± 2.6 Lo
ower/Early Devonian
Carboniferous
Paleozoic Era (542 Ma - 252 Ma)
359.2 ± 2.5 - 326.4 ± 1.6
Mississipian*
Carboniferous
318.1 ± 1.3 - 303.9 ± 0.9
Pennsylvanian*
299.0 ± 0.8 - 275.6 ± 0.7 C
Cisuralian
270.6 ± 0.7 - 265.8 ± 0.7 Gu
uadalupian Permian
260.4 ± 0.7 - 253.8 ± 0.7 L
Lopingian
Phanerozoic (542 Ma - present)
251.0 ± 0.7 - 203.6 ± 1.5 Triassic*
199.6 ± 0.6 - 150.8 ± 4.0 Jurassic*
Ma)
145.5 ± 4.0 - 112.0 ± 1.0 Low
wer/Early*
Cretaceous
(251 Ma - 65
Mesozoic Era
99.6 ± 0.9 - 70.6 ± 0.6 Up
pper/Late*
K-T Mass Extinction
T
65.5 ± 0.3 - 58.7 ± 0.2 Pa
aleocene
T
55.8 ± 0.2 - 37.2 ± 0.1 Eocene
T
Paleogen
33.9 ± 0.1 - 28.4 ± 0.1 O
Oligocene
T
23.03 ± 0.05 - 7.246 ± 0.05 M
Miocene
T
present)
5.332 ± 0.005 - 3.600 ± 0.005 P
Pliocene
Q
2.588 ± 0.005 - 0.126 ± 0.005 Ple
eistocene
Cenozoic Era (65 Ma-
Neogene
Q
0.011430 ± 0.00013 Ma - now Holocene
(‐ept)
Global distribution of Entisols
2. INCEPTISOLS
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The subsoil in this soil is
permanently under water.
In the absence of oxygen a
bluish color develops in the
soil and is evidence for
reduction
The Inceptisols have horizons in early stage of formation.
Inceptisols form under a variety of climates except aridic
Some are wet soils and used for rice cultivation. Others may
conditions.
occur on slopes of hills or mountains.
Soil moisture regimes can be variable ranging from poorly
drained soils to well‐drained soils on steep slopes.
Climate which inhibits soil development such as low
temperatures or low precipitation favors the development
of Inceptisols.
The suborder of Aquepts requires higher soil moisture
conditions compared to the other suborders of
Inceptisols.
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Global distribution of Inceptisols
Parent Material:
Inceptisols are extensive in areas of glacial deposits or on
recent deposits in valleys or deltas.
They occupy upland positions on young geomorphic
surfaces, both primary and secondary minerals are
present.
Most Inceptisols are present on geologically young
sediments (e.g. alluvium, colluvium, loess).
Parent materials which is highly calcareous or resistant to
weathering inhibit soil development but favor the
development of Inceptisols.
3. MOLLISOLS
(‐oll)
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The Mollisols are the Prairie soils. They have a dark
surface horizon, very friable and easy to cultivate. The
soil is generally deep and may have some special
features.
The white subsoil is due to
the presence of a calcic
horizon
Global distribution of Mollisols
4. ALFISOLS
(‐alf)
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The Alfisols are well structured deep soils and
generally very fertile. They support a good vegetation
and in most parts of the world are used for agriculture.
The ‘B’ horizon has well
developed columnar structure
Global distribution of Alfisols
5. ULTISOLS
(‐ult)
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The Ultisols are mainly in the humid parts of the
world. They have a subsoil with more clay (or and argillic
horizon) and are generally acid.
Ultisol from Taiwan is a rice‐
growing soil and has reddish
mottles called plinthite.
Global distribution of Ultisols
6. OXISOLS
(‐ox)
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The Oxisols are found in the tropics, generally
yellowish to reddish in color, deep, loamy to clayey, and
the natural vegetation is forest.
Global distribution of Oxisols
7. VERTISOLS
(‐ert)
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Characteristic feature of soils
are slickensides , which are
arranged in a curvi‐linear
In Vietnam Vertisol structural polygons are exposed to the sun
to form seedbed material
manner.
Global distribution of Vertisols
The Vertisols are formed on sediments rich in
smectites (2:1 clay). Smectites swell when moist and
shrink when dry and this property has implications for
structures built on this soil.
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8. ANDISOLS
(‐and)
The Andisols develop on volcanic deposits under
different climates. Many of them are stratified indicating
different periods of pyroclastic deposition.
A buried soil and there was a
period of a few thousand years
prior to the more recent
deposition. During this
period, vegetation was
established and an organic
rich surface horizon formed.
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Global distribution of Andisols
9. HISTOSOLS
(‐ist)
The Histosols are formed by accumulation of organic
matter in a water‐logged basin or under a cold humid
climate or both.
from Greek
“Histos = tissue”
“ i i ”
Formed under conditions of
water saturation. Water
stands in the pit. Histosols in Sumatra
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comprises soils formed in ‘organic soil material’. These vary from soils developed in moss peat
Parent material: (boreal, arctic and subarctic regions), reeds/sedge
incompletely decomposed plant remains, with peat and forest peat (temperate regions),
or without admixtures of sand, silt or clay. mangrove peat and swamp forest peat (humid
tropics).
Found at all altitudes but the vast majority occurs
‘Organic soil material’ is soil material that contains
in lowlands.
more than 20 percent organic matter by weight,
roughly equivalent to 30 – 35 percent by volume. Common international names are ‘peat soils’,
‘muck soils’, ‘bog soils’ and ‘organic soils’.
Elsewhere, they are confined to poorly drained The exceptionally large total pore volume of Histosols
(typically > 85%), their perishable nature and their
basins, depressions, swamps and marshlands with
normally poor chemical properties pose formidable
shallow groundwater, and highland areas with a problems to farmers and others concerned with conserving
high precipitation/evapotranspiration ratio. use of Histosols.
Organic soil materials that formed in different
g Fibric Histosols are loosely p
y packed in their natural state,
environments are generally of different botanical with a bulk density (ρ) that is typically between 0.05 and
composition; degrees of decomposition and 0.15 Mg/m3.
contents of mineral admixtures are equally varied. Wide variation in chemical properties: Extremely acid
Histosols, with a field‐pH value around 3, have been
observed in coastal regions where pyrite (FeS2) containing
peat bogs were drained. Alkaline peat (field‐pH around
7.8) has been reported from the Maldives.
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Use: Use:
Sustainable use of peat lands is limited to extensive If carefully managed, Histosols can be very
forms of forestry or grazing productive under capital‐intensive forms of arable
In places, peat bogs are mined, e.g. for production cropping/horticulture, at the cost of sharply
horticulture,
of growth substrate for horticulture or to fuel increased mineralization losses.
power stations.
Deep peat formations and peat in northern regions
are best left untouched.
PROBLEM !!!
The exceptionally large total pore volume of Histosols (typically > 85%),
their perishable nature and their normally poor chemical properties Grasses,
pose formidable problems to farmers and others concerned with ferns
conserving use of Histosols. Reeds,
sedges
Aquatic
plants
Fibric Histosols are loosely packed in their natural state, with a bulk
density (ρ) that is typically between 0.05 and 0.15 Mg/m3.
Wide variation in chemical properties: Extremely acid Histosols, with a
field‐pH value around 3, have been observed in coastal regions where
pyrite (FeS2) containing peat bogs were drained. Alkaline peat (field‐
pH around 7.8) has been reported from the Maldives.
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Grasses,
shrubs
Mixed swamp
forest
Grasses,
ferns
Reeds,
sedges
Aquatic
plants
Global distribution of Histosols
10. SPODOSOLS
(‐od)
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Typical feature is a bleached
layer underlain by a dark
organic rich layer.
The Spodosols are probably the most photogenic
soils with several kinds of horizons, each with its own
color, texture, and properties.
Histosols in Sumatra
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Global distribution of Spodosols
11. ARIDISOLS
(‐id)
“Salt caps”
The white layer in the subsoil
is a calcic horizon or an
accumulation of calcite.
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Global distribution of Aridisols
The Aridisols occur in the deserts and the soil does
not moisten for more than a few weeks a year. Under
such conditions, salts and other minerals accumulate in
the soil
12. GELISOLS
(‐el)
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The Gelisols occur in the tundra zone of northern
latitudes or at very high elevations. The subsoil may be
permanently frozen or frozen for long periods during the
year.
An ice layer forms the
subsoil of this Gelisol
from Alaska
Global distribution of Gelisols
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