Transcript Document

Soil Classification
NR 200
Chapter 3
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Why classify?
 Soils
are classified on the basis of
their profile characteristics:
Moisture, temperature, color,
texture, structure, organic matter,
clay, iron, salts, pH, percentage of
base saturation and soil depth.
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Individual soils:
Pedon – and individual soil profile 1- 10 m2
 Polypedon – a group of pedons
 When a polypedon has related
characteristics of the profile then we can
call it a :

soil
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series.
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Many terms are used to describe
soils:


Epipedons – top portion
Ochric – light colored, low organic matter and
may be massive structure when dry.
Histic – High organic matter
Subsurface
Duripan – hardpan cemented by silica
Fragipan – brittle pan, loamy to silty in
texture
Salic – Accumulation of salts
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Many terms are used to describe soils:
continued
Soil moisture

Ustic – soil moisture available during the
growing season but dry drought periods
will occur.
Xeric – moist cool winters and dry summers
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Taxonomy of Soil Science:
The systematic evaluation of
the properties of the soil.
Just like all living organisms.
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Alfisols – Soils with an
accumulation of clay
in the B horizon.
The older soils between
the rivers
 - O, A, E, Bt (t is clay
accumulation) and C

Ca series: Dinuba,
Modesto, San Joaquin,
Fresno, Montpellier

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Alfisols are in semiarid to moist areas.
These soils result from weathering
processes that leach clay minerals and
other constituents out of the surface
layer 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.
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Andisols –
Volcanic soils
(ash, cinders,
pumice and
basalt)– Hawaii,
Northern
California
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Andisols
form
from
weathering
processes that generate minerals with
little
crystalline
structure.
These
minerals can result in an unusually high
water- and nutrient-holding capacity.
As a group, Andisols tend to be highly
productive soils. They include weakly
weathered soils with much volcanic
glass as well as more strongly
weathered soils. They are common in
cool areas with moderate to high
precipitation, especially those areas
associated with volcanic materials.
Andisols make up about 1% of the
world’s ice-free land surface.
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Aridisols –
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Arid Western soils
low organic soils.
Moisture is
inadequate to
mature a crop
without irrigation in
most years.
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Aridisols are soils that are too dry for
the growth of mesophytic plants. The
lack of moisture greatly restricts the
intensity of weathering processes and
limits most soil development processes
to the upper part of the soils. Aridisols
often accumulate gypsum, salt, calcium
carbonate, and other materials that are
easily leached from soils in more humid
environments.
Aridisols are common in the deserts of
the world.
Aridisols make up about 12% of the
world’s ice-free surface.
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Entisols – Very young soils,
with C horizon and maybe a
slight developed A horizon
The Entisol soils that are formed from
alluvial fans are some of the most
productive soils in the world. Irrigated
farming on the good young Valley soils
produces crops in great abundance.
California Series:
Hanford, Delhi,
Tujunga, Zacharis,
White Rock
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Entisols are soils that show little
or no evidence of pedogenic
horizon development.
Entisols occur in areas of
recently deposited parent
materials or in areas where
erosion or depositions rates are
faster than the rate of soil
development; such as dunes,
steep slopes, and flood planes.
They occur in many
environments.
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Entisols make up about 16% of
the world’s ice-free land surface.
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Gelisols –
permafrost soils,
tundra slowly
aging.
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Gelisols are soils that have
permafrost near the soil
surface and/or have evidence
of cryoturbation (frost churning)
and/or ice segregation.
Gelisols are common in the
higher latitudes or at high
elevations.
Gelisols make up about 9% of
the world’s ice-free land
surface.
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Histosols –
Organic soils over
20% OM –Delta
area
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Histosols have a high content of
organic matter and no permafrost.
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.
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Histosols make up about 1% of the
world’s ice-free surface.
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Inceptisols –
Young soils but older
then Entisols A-C
horizon with the
beginning formation
of a B layer.
Hilmar Series
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Inceptisols are soils of semiarid
to humid environments that
generally exhibit only moderate
degrees of soil weathering and
development.
Inceptisols have a wide range in
characteristics and occur in a
wide variety of climates.
Inceptisols make up about 17%
of the world’s ice-free land
surface.
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Mollisols –
Most soils have developed under
grass vegetation, Prairie soils
Mineral soils with thick, dark surface
horizons relatively high in organic
matter and with high base
saturation. The great Mid-West
grain belt is predominately this
order.
Ca series: Grangeville,
Sorrento
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Mollisols are soils that have a dark
colored surface horizon relatively high
in content of organic matter. The soils
are base rich throughout and therefore
are quite fertile.
Mollisols characteristically 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.
Mollisols make up about 7% of the
world’s ice-free land surface.
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Oxisols –
Highly weathered
soils old soils with
high pH , Tropical Hawaii
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Oxisols are highly weathered soils of
tropical and subtropical regions. They
are dominated by low activity minerals,
such as quartz, kaolinite, and iron
oxides. They tend to have indistinct
horizons.
Oxisols characteristically occur on land
surfaces that have been stable for a
long time. They have low natural
fertility as well as a low capacity to
retain additions of lime and fertilizer.
Oxisols make up about 8% of the
world’s ice-free land surface.
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Spodosols –
Light colored, acid forest
cool humid regions
generally infertile, high
altitudes with heavy
precipitation.
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Spodosols formed from weathering processes
that strip organic natter combined with
aluminum (with or without iron) form 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 coarsetextured deposits under coniferous forests of
humid regions. They tend to be acid and
infertile.
Spodosols make up about 4% of the world’s
ice-free land surface
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Ultisols –
Highly weathered
soils found in the
Southwestern US.
Lower Sierra soils
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Ultisols 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.
Ultisols are typically acid soils in which
most nutrients are concentrated in the
upper few inches. They have a
moderately low capacity to retain
additions of lime and fertilizer.
Ultisols make up about 8% of the
world’s ice-free land surface.
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Vertisols –
High in swelling
clays, when soils dry
exhibit a great deal of
cracking.
California: Capay, Stockton
series
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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.
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Vertisols make up about 2% of the
world’s ice-free land surface.
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Using the Terminology
Soil Order
Alfisols
Andisols
Aridisols
Entisols
Gelisols
Histosols
Inceptisols
Mollisols
Oxisols
Spodosols
Ultisols
Vertisols
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Formative Terms
Alf, Meaningless syllable
Modified from ando
Latin, aridies, dry
Ent, meaningless
Latin gelare, to freeze
Greek, histos, tissue
Latin, incepum, beginning
Latin, mollis, soft
French oxide
Greek spodos, wood ash
Latin ultimus, last
Latin verto, turn
Pronunciation
Pedalfer
Ando
Arid
Recent
Jell
Histology
Inception
Mollify
Oxide
Odd
Ultimate
Invert
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Using the Terminology
The ending of the taxonomic soil term will indicate
which order it belongs to; ie using the taxonomic
name of a soil such as:
Modesto Series- Mollic Haploxeralfs
(Scientific name)
meaning it comes from the Alfisol order.
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Determine the orders for the following soils.
Tujunga Series - Typic Xeropsamments
Entisols
meaning it is ___________
order
Peter Series -
Typic Haploxerolls
Mollisols order
meaning it is ____________
Keyes Series - Abruptic Durixeralfs
Alfisols order
meaning it is ____________
Hilmar Series - Aeric Halaquepts
Inceptisols order
meaning it is ____________
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Land Capability Classes – a
method of determining a soil’s
ability to grow certain types of
crops.
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The criteria for placing a given area in a
particular class involves the landscape
locationslope of the field, depth, texture, and
reaction of the soil.
The remaining four classes, V thru VIII, are
not to be used for cropland, but may have
uses for pasture, range, woodland, grazing,
wildlife, recreation, and esthetic purposes.
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Exerpt from A. A. Klingebiel and P. H.
Montgomery, Land Capability
Classification, Agriculture Handbook No.
210 (Washington, DC: Soil Conservation
Service, U.S. Department of Agriculture,
1961), pp. 1-3.
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I: Can grow anything
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II: Can grow most anything once
minor soil problems are
addressed
2-6% slope
 shallow soils
 minor saline or alkali
conditions
 slight drainage problems

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III: Good soils that have more
moderate problems
6-12% slope
 erosion concerns
 very shallow soil
 low fertility
 moderate saline and alkaline conditions

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IV: Pasture to grass hays
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V-VIII: Little agriculture value
except for pasture for grazing
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Letters for further understanding
e - erosion factor
 w – wetness
 s – stony, tillage difficulties, shallow or
saline

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Storie Index Rating
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Factor A
Physical Profile and based on their
physiological location
 Recent Alluvial fans, young alluvial fans,
older alluvial fans, older plains and upland.

Based on the degree of soil profile
development
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Factor B

Surface texture - Fine Sandy Loam, Loam
and Silt Loam = 100
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Factor C

Slope 0-2% = 100
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Factor X
Drainage
 Alkali
 Fertility
 Acidity
 Erosion
 Microrelief

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Grading
Grade 1 Excellent 100-80
 Grade 2 Good 60-79
 Grade 3 Fair 40-59
 Grade 4 Poor 20-39
 Grade 5 Very Poor 10-19
 Grade 6 Nonagricultural less then
10

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Example using the Storie index system:
Young Alluvial Flood plains slightly
Factor A (Physical Profile) = ___________
developed profile 95-100 - 100%
Sandy Loam – 95%
Factor B (Surface Texture) = _____________
Nearly Level – 100%
Factor C (Slope) = _____________
Nutrient level poor – 80-95 -90%
Factor X (Other Factors ) = _____________
Drainage, Alkali, Nutrient, Acidity, Erosion, Microrelief
1.00 X .95 X 1.00 X .90 = 85.5
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Which is a grade 1 Excellent soil
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