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

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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!

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

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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

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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

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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

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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

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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

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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

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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

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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 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 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

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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 is the climate like? What does the profile look like?) Subgroup name = Typic Albaqualf

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