Chapter 3 Learning Objectives
Soil Taxonomy
Diagnostic Subsurface Horizons
• 18 of them
• Six we will focus on (and the assoc. genetic
label):
– Albic ((E))
– Cambic (Bw)
– Spodic (Bhs)
- Argillic
g
((Bt))
- Fragic (Bx)
- Calcic (Bk)
• Describe the current USDA soil classification
system
• List the six categories of classification in Soil
Taxonomy
• Describe the major characteristics, the
general degree of weathering and soil
development, and the worldwide distribution
and uses of the 12 soil orders
• List key features of a particular soil and its
environment given the soil name (e.g.,
Hapludalf)
Diagnostic Subsurface Horizons
– Albic: light-colored elluvial horizon (leached)
– Cambic: weakly developed horizon, some color
change
– Spodic: illuvial horizon with accumulations of O.M.
– Argillic: subsurface accumulations of silicate clays
– Calcic:
C l i accumulation
l ti off carbonates,
b
t
often
ft as
white, chalk-like nodules
– Fragipan: cemented, dense, brittle pan
Light colored horizon
Albic
Weakly
developed horizon
Cambic
Argillic
No significant
accumulation
Chapter 3
Unweathered
material
silicate clays
Accumulation of
organic matter
Acid weathering,
Fe, Al oxides
Spodic
Calcic
Fragipan
Modified from full version of Figure 3.3 in textbook (page 62).
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Levels of Description
•
•
•
•
•
•
Order
Suborder
Great group
Subgroup
Family
Series
Most general
Most specific
Levels of Description
• Order – One name, all end in “-sol” There are 12 . . .
• Suborder – One name, last 2-3 letters
indicates the soil order. Tells something
about properties important to genesis and
plant growth (e.g., climate info) Example:
Aquent
•
•
•
•
Great group
Subgroup
Family
Series
Levels of Description
• Order – One name, all end in “-sol” There are 12 . . .
• Suborder –properties (e.g., climate info) AND which
Order
• Great group – 3 parts, adds info about the horizons
• Subgroup – TWO words. All info from above
plus whether it is “typical”
typical or shares
properties with another soil type. Example:
Mollic Psammaquent
• Family
• Series
Levels of Description
• Order – One name, all end in “-sol” There are
12. Differentiated by presence or absence of
diagnostic horizons or features that reflect
soil-forming processes. EXAMPLE:
ENTISOL
•
•
•
•
•
Suborder
Great group
Subgroup
Family
Series
Levels of Description
• Order – One name, all end in “-sol” There are 12 . . .
• Suborder –properties (e.g., climate info) AND order
• Great group – 3 pieces of info. Last 2-3 letters
tell the order, includes suborder info, and
adds info about the horizons (e.g., sandy,
cla e hard
clayey,
hard…)) Example:
E ample Psammaquent
Psammaq ent
• Subgroup
• Family
• Series
Levels of Description
• Order – One name, all end in “-sol” There are 12 . . .
• Suborder – Tells something about properties (e.g.,
climate)
• Great group – 3 parts, adds info about the horizons
• Subgroup – TWO words.
• Family – name includes about 5-6 words!
Adds physical and chemical properties that
affect growth of plants
• Series
2
Levels of Description
• Order – One name, all end in “-sol” There are 12 . . .
• Suborder – Tells something about properties (e.g.,
climate)
• Great group – 3 parts, adds info about the horizons
• Subgroup – TWO words.
• Family – name includes about 5-6 words!
Soil Taxonomy
Order
• Series – Often referred to by a single name
that doesn’t tell you anything unless you
already know it well.
12 Soil Orders
Fig 3.5
3
Soil Orders
Soil Order “Formative Characteristics,
element” location, etc.
Entisol
-ent
Inceptisol
Gelisol
Histosol
Andisol
Aridisol
-ept
-el
-ist
-and
-id
Entisols
Absence of distinct
pedogenic horizons;
climate & PM key
Soil Orders
Entisols
• Sandy, young soils
• Plainfield loamy sand:
Typic Udipsamment
Inceptisol: few horizons, inception
of B (Bw)
Lithic Eutrudept - northern
Michigan
Soil
Order
“Formativ Characteristics, location, etc.
e
element”
Entisol
-ent
Absence of distinct pedogenic
horizons; climate & PM key
Inceptisol
-ept
ept
Weak development,
development nothing
exciting. There is a “B”
horizon
Gelisol
Histosol
-el
-ist
Andisol
-and
Aridisol
-id
Soil Orders
Soil
Order
“Form. el” Characteristics, location, etc.
Entisol
-ent
Absence of pedogenic horizons
Inceptisol
-ept
Weak development
Gelisol
-el
Permafrost, freeze-thaw
f t
features
(13% off soils
il
worldwide!)
Histosol
-ist
Andisol
-and
Aridisol
-id
4
Gelisols: permafrost
Gelisols
• cryoturbation
Soil Orders
Gelisols
Soil
Order
“Form el” Characteristics, location, etc.
Entisol
-ent
Absence of distinct pedogenic
horizons
Inceptisol
-ept
Weak development
G li l
Gelisol
-ell
P
Permafrost,
f t freeze-thaw
f
th
Histosol
-ist
Very high OM in upper 80 cm
(peats), wet
Andisol
-and
Aridisol
-id
Histosols: organic soils
Histosols
• Wetland delineation
5
Soil Orders
Soil
Order
“Form el” Characteristics, location, etc.
Entisol
-ent
Absence of horizons
Inceptisol
-ept
Weak development
Gelisol
-el
Permafrost freeze-thaw
Permafrost,
Histosol
-ist
Very high OM, wet
Andisol
-and
Aridisol
-id
Andisols
Volcanic soils, Al-humus
complexes, mild temp, fairly
moist
Soil Orders
Andisols
Soil
Order
Ending Characteristics, etc.
Entisol
-ent
Inceptisol
-ept
Absence of distinct pedogenic
horizons
Weak development
Gelisol
-el
Permafrost, freeze-thaw
Histosol
-ist
Very high OM, wet
Andisol
-and
Aridisol
-id
Volcanic soils
No avail. H2O when plants growing –
the largest group of soils on Earth!
Aridisols: dry soils
Aridisols
• 12% globally
• 9% US
6
Vertisol: swelling and cracking
clays
Soil Orders
Soil Order “Formative Characteristics,
element” location, etc.
Vertisol
-ert
Mollisol
-oll
oll
Ultisol
-ult
Alfisol
Spodosol
-alf
-od
Oxisol
-ox
Swelling clays, high
BS, dry-wet
Vertisols
Soil Orders
Vertisols
Soil
Order
Ending Characteristics, location, etc.
Vertisol
-ert
Swelling clays, high BS
Mollisol
-oll
Dark, thick epipedon, grasslands,
some dry period
period, high BS
Ultisol
-ult
Alfisol
-alf
Spodosol
-od
Oxisol
-ox
7
Mollisol: dark, grassland, high base sat.
• Loess: silt
• 22% of US
• Very productive
Mollisols
Plate 8 Mollisols -- a Typic Hapludoll from central
Iowa. Mollic epipedon to 1.8 ft. Scale in feet.
Soil Orders
Soil
Order
Ultisols
Ending Characteristics, etc.
Vertisol
-ert
Mollisol
-oll
Dark, thick, grasslands
Ultisol
-ult
Wet subtropical
p
or tropical,
p , highly
g y
acidic, high in clay, Fe and Al
oxides, productive if add fertilizers
Alfisol
-alf
Spodosol
-od
Oxisol
-ox
Swelling clays, high BS
Soil Orders
Ultisols: Bt w/ low bases
• More
leached than
Alfisols
• Less fertile
Soil
Order
Vertisol
Mollisol
Ending Characteristics, etc.
-ert
-oll
Swelling clays, high BS
Dark, thick, grasslands
Ultisol
-ult
subtropical,
p , acidic,, high
g in clay,
y, Fe,, Al
Alfisol
-alf
Moist, forested, mildly acidic,
translocation of clays,
moderate-high BS
Spodosol
-od
Oxisol
-ox
8
Alfisols: Bt, ochric epipedon
Alifsols
Soil Orders
Soil
Order
Endin Characteristics, etc.
g
Vertisol
-ert
Swelling clays, high BS
Mollisol
Ultisol
-oll
-ult
Dark, thick, grasslands
Moist & warm, acidic, high in clay,
oxides
Alfisol
-alf
Moist, forested, clays
Spodosol
-od
Translocation of humus and Al,
Fe, cool, wet, sandy, coniferous
forest
Oxisol
-ox
Spodosol: Bs, Bh or Bhs, albic
horizon
Spodosols
Spodosols
• Northern Wis
– Orthods: typical
of central
concept of
Spodosols
9
Soil Orders
Soil
Order
Oxisols
Ending Characteristics, etc.
Vertisol
-ert
Mollisol
-oll
Swelling clays, high BS
Dark, thick, grasslands
Ultisol
-ult
Moist & warm, acidic . . .
Alfisol
-alf
Moist, forested, clays
Spodosol
Oxisol
-od
-ox
cool, wet, sandy, acidic . . .
Extreme weathering, tropical forest, Fe,
Al oxides, old, stable PM
Oxisols
• Tropical
• Highly weathered
Development and soil orders
Development of the soil orders
Bk
ice
Bo
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The SUPER SIMPLIFIED guide to soil orders
1. If no subsurface horizons Æ Entisol
2. If aridic moisture regime and NOT and
Entisol Æ Aridisol
3. If mollic epipedon Æ Mollisol
pp
Æ Histosol
4. If histic epipedon
5. If permafrost Æ Gelisol
The SUPER SIMPLIFIED guide (cont.)
6. If on volcanic material Æ Andisol
7. If TONS of clay, with shrink-swell features
(“slickensides,” large cracks when dry) Æ
Vertisols
8 If spodic horizon (Bh
8.
(Bh, Bs) Æ Spodosols
9. If oxic horizon (Bo) Æ Oxisols
The SUPER SIMPLIFIED guide (cont.)
10. If umbric epipedon (low BS), argillic horizon,
subtropical location Æ Ultisol
11. If ochric epipedon (sometimes umbric),
argillic horizon, often an albic horizon, and a
cool, moist climate Æ Alfisol
12 If ochric
12.
h i epipedon
i d and
d NOT an E
Entisol
ti l or
Aridisol, often a cambic horizon Æ
Inceptisol
Soil Taxonomy
Suborder
11
Suborders
• Often described based on climatic
information
• Name of the suborder tells what order
the soil belongs to PLUS one other
feature of the soil (usually climate
climate,
except for Aridisols…)
Soil Temperature Regimes
Soil Moisture Regimes
• Aquic – saturated for extended periods
WET
• Udic – not dry for more than 90 days
• Ustic – dry 90-180 days
• Xeric – dry summer
summer, moist winter
• Aridic – moist <90 days
• Torric (not a real moisture regime but used in
names like one. dry + hot )
DRY
Suborders
• Often described based on climatic information
–
–
–
–
–
–
–
Aqu - wet
Ud - moist
Ust - dry
Xer – moist winter, dry summer
Torr – hot and dry
Cry – very cold
Hist – histic epipedon
•
•
•
•
•
•
Pergelic - < 0oC
Cryic – 0-8, cold summer
Frigid – 0-8, warm summer
Mesic – 8-15
Thermic – 15-22
Hyperthermic - >22
COLD
HOT
• Iso-(frigid, mesic, thermic, hyperthermic):
small difference between summer and winter
Suborders (cont.)
Also differentiated based on key features
• Fluv: fluvial, from a river
• Psamm: sandy
• Alb: albic horizon ((E)) – leached
• Arg: argillic horizon (Bt) – clayey
• Orth: “other” or “true to the definition”
• Example: Aqualf (note capitalization)
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Examples of suborders
Examples of suborders
(see Table 3.3 of text for more)
•
•
•
•
•
•
Entisols
Aquents
Fluvents
O
Orthents
Psamments
Mollisols
Albolls
Aquolls
C
Cryolls
Udolls
Ustolls
Xerolls
•
•
•
•
•
Oxisols
Aquox
Torrox
Udox
Ustox
Vertisols
Aquerts
Cryerts
Uderts
Usterts
Xererts
Soil Taxonomy
Great group
Great Groups
• Subdivisions of suborders. Name has 3
pieces of information. SINGLE WORD
• Defined largely by the presence or
absence of diagnostic horizons and the
arrangement of those horizons (see text
Table 3.4)
Great Groups
• Divisions of suborders. 3 pieces of info. SINGLE
word
• diagnostic horizons key
• Example: Argiudoll
Order = Mollisol
Suborder = Udoll (moist)
Great group tells you there is an argillic
horizon
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Soil Taxonomy
Formative elements for Great Group
• Argi: clay
• Calc: calcic (calcium carbonate, Bk
horizon!)
• Dur: hard
• Hapl: minimal development or simple
• Hum: humic materials
• Plus ones learned for suborder level
(psamm, cry, fluv, torr, . . .)
Family
Families
Soil Taxonomy
• Differentiated by particle size,
mineralogy, CEC, and temperature
classes
• Example:
– fine-loamy,
fi l
mixed,
i d mesic,
i U
Ustollic
t lli
Haplargid
Series
Series
• The most specific unit of the classification
system
• A subdivision of the family
• Each series defined by a specific range of soil
properties: usually kind, thickness, and
arrangement of horizons
• Name usually from a town or river or county
• Example: Kewaunee
– This happens to be a fine, mixed, mesic, Typic
Hapludalf at the family level
14
EXAMPLE TEST QUESTION
• Given the following SUBGROUP name,
identify the soil ORDER and
SUBORDER.
• Describe the soil as best you can.
(What vegetation type is most likely?
What is the climate like? What does the
profile look like?)
Subgroup name = Typic Albaqualf
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