Download Introduction to Soil Classification

Introduction to Soil Classification
Debbie Surabian
State Soil Scientist CT/RI
USDA - NRCS
Soil Taxonomy
Soil Taxonomy was developed by the
USDA Soil Conservation Service staff
between 1951 and 1975.
Soil Taxonomy
Soil Taxonomy was designed to classify all the world's soils because
expanding soil survey programs demanded more precise definitions
of soil properties.
– Organize knowledge of soils with similar properties
– Facilitate communication among pedologists
– Transfer information and technology
Soil Taxonomy
• Adopted in 1965 by Dr. Guy D. Smith, USDA
• Official soil classification system of the United States
• Has been recognition as a possible universal system for
classifying soils.
• To date, no system of classification has world wide
acceptance – World Reference Base for Soil Resources
(WRB)
Criteria Used in Soil
Taxonomy
• Based on soil properties that can be observed and
measured.
• Chemical, physical, and biological properties such as
moisture, temperature, texture, structure, pH, soil depth
• Presence or absence of certain diagnostic horizons
(surface and subsurface horizons)
The Soils That We Classify
The upper limit of soil is the boundary between
soil and air [or] shallow water…[not] too deep
(typically more than 2.5 meters) for the growth of
rooted plants.
The Soils That We Classify
For purposes of classification, the lower boundary
of soil is arbitrarily set at 200 centimeters.
Hierarchical System of
Soil Taxonomy
Order (12) – Most general, based on soil forming processes.
Sub-Orders (70) – Based on similarities in soil formation (moisture/temp/other).
Great Groups (344) – Based on differences between soil horizons (diagnostic
horizons).
Sub-Groups (2,664) – Profile characteristics.
Family (~11,332) – Based on properties that effect management (mineralogy,
temperature)
Series (~23,600) – Most specific, based on kind and arrangement of horizons.
Phase – Field mapping units (stony, slope, other), not a category in soil taxonomy.
Windsor Series
Mixed, mesic
Family
Mixed Mineralogy
Mean Annual
Temp. 8 – 15c
Typic
Udipsamments
Sub
Order
Sub
Group
Sandy
Reflects
Central Concept
Great
Group
Humid Climate
Order
Entisol
Twelve Soil Orders
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Entisol
Inceptisol
Andisols
Spodosols
Mollisols
Alfisols
Ultisols
Oxisols
Aridisols
Vertisols
Histosols
Gelisols
Soil Orders
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Highest level of classification
Broadest group
12 orders
Based on diagnostic horizons and climate
Degree of weathering and soil development in
the different soil orders
Soil Taxonomy
Global Distribution
Entisols – 18%
Inceptisols – 15%
Mollisols – 7%
Spodosols – 4%
Histosols – 1%
Entisols
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Recent
Very recent or young soils
Little or no profile development
No diagnostic subsurface horizons
Form on
• resistant parent materials,
• mine spoils,
• steep slopes,
• floodplains
Windsor Series
Entisols
• Simple soils to very productive alluvial soils
• Pedogenically featureless (between “not soil” and
horizonated soil)
• Generally associated with human transported
materials
Is it Soil?
No: active
gravel pit
No: pavement
and buildings
Yes: vegetated area,
Fortress Series.
Entisols – Six Suborders
TYPIC UDIFLUVENTS
TYPIC UDORTHENTS
Hadley Series
Manchester Series
Inceptisols
• inception (Latin, beginning)
• Slightly more development than
Entisols
• Young soils but beginning of profile
development is evident
• May have a cambic horizon
Gloucester Series
Inceptisols – Seven Suborders
AQUIC DYSTRUDEPTS
TYPIC ENDOAQUEPTS
Scitico Series
Sutton Series
Mollisols
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mollis (Latin, soft)
Very dark-colored soils
Naturally fertile soils
Typically form under grasslands
Has a mollic epipedon:
• Thick, humus-rich surface
horizon
• High % base saturation
throughout profile
Mollisols – Eight Suborders
TYPIC
ARGIUDOLL
Sharpsburg
Series
TYPIC ENDOAQUOLLS
Menlo Series
Spodosols
• From Greek spodos, “wood ash”
• Acid soils with low fertility
• Form in humid, cool climates and
occur most often in conifer forests
(New England, Mich., Canada)
• Form in acid, coarse, quartz
(sandy) bearing P.M.
• Has a spodic horizon
• Accumulations of organic
matter and/or iron/aluminum
oxides in the subsoil
Spodosols – Five Suborders
AQUODS
AQUODS
Histosols
• histos “tissue”
• Organic soils derived from hydrophytic
plants
• Low bulk density and very high water
holding capacity
Histosols – Five Suborders
Alfisols
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pedalfer
Naturally fertile soils
High base saturation
Clay-enriched subsoil horizon
Aridisols
• arid (Latin, dry)
• Form in aridic soil moisture
regimes (dry)
• Low OM
• Little leaching
Ultisols
• -ultimate (Latin, last)
• Old, highly weathered, high
degree of development
• Low fertility
Vertisols
• invert (Latin, turn)
• High clay soils (>30%
sticky shrink-swell clays)
• Deep cracks upon drying
• Materials from soil surface
fill cracks and become part
of the subsurface when the
cracks close (inverted soil)
Andisols
• ando (Japanese, black soil)
• Form from P.M. of volcanic
origin
• Young soils
• Can have unusually low bulk
densities
• High water holding capacity
Oxisols
• oxide (French, oxide)
• Very highly weathered soils
• Intense red or yellow color
(high in oxidized iron)
• Low native fertility
Gelisols
• gelid (Greek, cold)
• Young soils with little profile
development
• High organic carbon content
Series
• Soil series predates Soil Taxonomy – used since 1899
• In 1975 there were 10,500 series in the U.S. and its territories;
compared to about 23,600 series today
• Lowest level of classification – can be subdivided into Phases
• Typically name based on location where first identified
Period of Soil Taxonomy
Order
Sub
Order
Great
Group
Sub Family
Group
Series
Whitman Series
Loamy, mixed, active,
acid, mesic, shallow
Family
Particle Size Class
Mixed Mineralogy
Clay Activity Class
Reaction Class
Mean Annual Temp. 8-15c
Soil Depth class (to Cd)
Typic
Sub
Group
Reflects
Central Concept
Humaquepts
Sub
Order
Aquic
Order
Great Group
Inceptisol
Accumulation of Organic
Matter in the Surface
Deb’s Tips and Tricks to
using Soil Taxonomy
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Start from the beginning and work your way through the keys
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If the criteria are not met, continue in order until they are met
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Read and re-read each sentence
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Use the Official Series Descriptions (OSDs) to learn how to key out pedons
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Don’t assume the pit you dig will be a perfect match to any OSD pedon
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Learn what you need to describe in the pit to classify your soil
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Review Ch. 18 - nice explanation on designation for horizons and layers