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Chapter 3

Soil Taxonomy

Chapter 3 Learning Objectives• 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 soilgeneral 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• 18 of them• Six we will focus on (and the assoc. genetic

label):

– Albic (E) - Argillic (Bt)( ) g ( )– Cambic (Bw) - Fragic (Bx)– Spodic (Bhs) - Calcic (Bk)

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

C l i l ti f b t ft– Calcic: accumulation of carbonates, often as white, chalk-like nodules

– Fragipan: cemented, dense, brittle pan

Argillic

Albic

Cambic

Unweathered

Light colored horizon

Weakly developed horizon

silicate claysNo

sign

ifica

nt

accu

mul

atio

n

FragipanCalcic

SpodicUnweathered

materialAcid weathering,

Fe, Al oxidesAccumulation oforganic matter

Modified from full version of Figure 3.3 in textbook (page 62).

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Levels of Description• Order• Suborder• Great group• Subgroup

Most general

• Family• Series

Most specific

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

• SuborderSuborder• Great group• Subgroup• Family• Series

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: AquentAquent

• 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 ) E ample Psammaq entclayey, hard…) Example: Psammaquent

• 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” or sharesplus whether it is 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 . . .• 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

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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!• Series – Often referred to by a single name

that doesn’t tell you anything unless you already know it well.

Soil Taxonomy

Order

12 Soil Orders

Fig 3.5

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Soil OrdersSoil Order “Formative

element”Characteristics, location, etc.

Entisol -ent Absence of distinct pedogenic horizons; climate & PM key

Inceptisol -eptGelisol -elHistosol -istAndisol -andAridisol -id

Entisols

Entisols• Sandy, young soils• Plainfield loamy sand:

Typic Udipsamment

Soil OrdersSoil Order

“Formative

element”

Characteristics, location, etc.

Entisol -ent Absence of distinct pedogenic horizons; climate & PM key

Inceptisol -ept Weak development nothingInceptisol ept Weak development, nothing exciting. There is a “B” horizon

Gelisol -elHistosol -istAndisol -andAridisol -id

Inceptisol: few horizons, inception of B (Bw)

Lithic Eutrudept - northern Michigan

Soil OrdersSoil Order

“Form. el” Characteristics, location, etc.

Entisol -ent Absence of pedogenic horizonsInceptisol -ept Weak development

Gelisol -el Permafrost, freeze-thaw f t (13% f ilfeatures (13% of soils worldwide!)

Histosol -istAndisol -andAridisol -id

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Gelisols: permafrost

• cryoturbation

Gelisols

GelisolsSoil Orders

Soil Order

“Form el” Characteristics, location, etc.

Entisol -ent Absence of distinct pedogenic horizons

Inceptisol -ept Weak developmentG li l l P f t f thGelisol -el Permafrost, freeze-thawHistosol -ist Very high OM in upper 80 cm

(peats), wetAndisol -andAridisol -id

HistosolsHistosols: organic soils

• Wetland delineation

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Soil Orders

Soil Order

“Form el” Characteristics, location, etc.

Entisol -ent Absence of horizonsInceptisol -ept Weak developmentGelisol -el Permafrost freeze-thawGelisol -el Permafrost, freeze-thawHistosol -ist Very high OM, wet

Andisol -and Volcanic soils, Al-humus complexes, mild temp, fairly moist

Aridisol -id

Andisols

AndisolsSoil Orders

Soil Order

Ending Characteristics, etc.

Entisol -ent Absence of distinct pedogenic horizons

Inceptisol -ept Weak developmentGelisol -el Permafrost, freeze-thawHistosol -ist Very high OM, wetAndisol -and Volcanic soilsAridisol -id No avail. H2O when plants growing –

the largest group of soils on Earth!

AridisolsAridisols: dry soils

• 12% globally• 9% US

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Soil OrdersSoil Order “Formative

element”Characteristics, location, etc.

Vertisol -ert Swelling clays, high BS, dry-wet

Mollisol ollMollisol -ollUltisol -ultAlfisol -alfSpodosol -odOxisol -ox

Vertisol: swelling and cracking clays

Vertisols

VertisolsSoil Orders

Soil Order

Ending Characteristics, location, etc.

Vertisol -ert Swelling clays, high BS

Mollisol -oll Dark, thick epipedon, grasslands, some dry period high BSsome dry period, high BS

Ultisol -ultAlfisol -alfSpodosol -odOxisol -ox

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Mollisol: dark, grassland, high base sat.

• Loess: silt• 22% of US• Very productive

Mollisols

Plate 8Plate 8 Mollisols Mollisols ---- a Typic Hapludoll from central a Typic Hapludoll from central Iowa. Mollic epipedon to 1.8 ft. Scale in feet.Iowa. Mollic epipedon to 1.8 ft. Scale in feet.

Soil OrdersSoil Order

Ending Characteristics, etc.

Vertisol -ert Swelling clays, high BSMollisol -oll Dark, thick, grasslands

Ultisol -ult Wet subtropical or tropical, highly p p , g yacidic, high in clay, Fe and Al oxides, productive if add fertilizers

Alfisol -alf

Spodosol -odOxisol -ox

Ultisols

Ultisols: Bt w/ low bases

• More leached than Alfisols

• Less fertile

Soil OrdersSoil Order

Ending Characteristics, etc.

Vertisol -ert Swelling clays, high BSMollisol -oll Dark, thick, grasslandsUltisol -ult subtropical, acidic, high in clay, Fe, Alp , , g y, ,

Alfisol -alf Moist, forested, mildly acidic, translocation of clays, moderate-high BS

Spodosol -odOxisol -ox

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Alifsols Alfisols: Bt, ochric epipedon

Soil OrdersSoil Order

Ending

Characteristics, etc.

Vertisol -ert Swelling clays, high BSMollisol -oll Dark, thick, grasslandsUltisol -ult Moist & warm, acidic, high in clay,

oxidesAlfisol -alf Moist, forested, clays

Spodosol -od Translocation of humus and Al, Fe, cool, wet, sandy, coniferous forest

Oxisol -ox

Spodosols

Spodosol: Bs, Bh or Bhs, albic horizon

• Northern Wis– Orthods: typical

of central concept ofconcept of Spodosols

Spodosols

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Soil OrdersSoil Order

Ending Characteristics, etc.

Vertisol -ert Swelling clays, high BSMollisol -oll Dark, thick, grasslandsUltisol -ult Moist & warm, acidic . . .Alfisol -alf Moist, forested, claysSpodosol -od cool, wet, sandy, acidic . . . Oxisol -ox Extreme weathering, tropical forest, Fe,

Al oxides, old, stable PM

Oxisols

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 orders1. If no subsurface horizons Entisol2. If aridic moisture regime and NOT and

Entisol Aridisol3. If mollic epipedon Mollisol4. If histic epipedon Histosolp p5. If permafrost Gelisol

The SUPER SIMPLIFIED guide (cont.)

6. If on volcanic material Andisol7. If TONS of clay, with shrink-swell features

(“slickensides,” large cracks when dry) Vertisols

8 If spodic horizon (Bh Bs) Spodosols8. If spodic horizon (Bh, Bs) Spodosols9. If oxic horizon (Bo) Oxisols

The SUPER SIMPLIFIED guide (cont.)

10. If umbric epipedon (low BS), argillic horizon, subtropical location Ultisol

11. If ochric epipedon (sometimes umbric), argillic horizon, often an albic horizon, and a cool, moist climate Alfisol

12 If h i i d d NOT E ti l12. If ochric epipedon and NOT an Entisol or Aridisol, often a cambic horizon Inceptisol

Soil Taxonomy

Suborder

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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 climatefeature of the soil (usually climate, except for Aridisols…)

Soil Moisture Regimes• Aquic – saturated for extended periods

• Udic – not dry for more than 90 days

• Ustic – dry 90-180 days

• Xeric – dry summer moist winter

WET

• Xeric – dry summer, moist winter

• Aridic – moist <90 days• Torric (not a real moisture regime but used in

names like one. dry + hot ) DRY

Soil Temperature Regimes• Pergelic - < 0oC• Cryic – 0-8, cold summer• Frigid – 0-8, warm summer• Mesic – 8-15• Thermic – 15-22

COLD

• Thermic – 15-22• Hyperthermic - >22

• Iso-(frigid, mesic, thermic, hyperthermic): small difference between summer and winter

HOT

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

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 (see Table 3.3 of text for more)

Entisols Mollisols• Aquents Albolls• Fluvents Aquolls

O C• Orthents Cryolls• Psamments Udolls• Ustolls• Xerolls

Examples of suborders Oxisols Vertisols

• Aquox Aquerts• Torrox Cryerts• Udox UdertsUdox Uderts• Ustox 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 textarrangement 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 = MollisolOrder = MollisolSuborder = Udoll (moist)

Great group tells you there is an argillic horizon

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Formative elements for Great Group• Argi: clay• Calc: calcic (calcium carbonate, Bk

horizon!)• Dur: hard• Hapl: minimal development or simple• Hapl: minimal development or simple• Hum: humic materials• Plus ones learned for suborder level

(psamm, cry, fluv, torr, . . .)

Soil Taxonomy

Family

Families• Differentiated by particle size,

mineralogy, CEC, and temperature classes

• Example: fi l i d i U t lli– fine-loamy, mixed, mesic, Ustollic Haplargid

Soil Taxonomy

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 horizonsarrangement 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

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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 vegetation type is most likely? What is the climate like? What does the profile look like?)

Subgroup name = Typic Albaqualf