Introduction to Soils and Soil Descriptions

Why do we need to know something about soils?

• Stability of the land surface

• Clues to past climate and vegetation

• Clues to terrestrial or aquatic environment

• Datable materials

• Document changes in geomorphic setting

• Mapping extent of sedimentary units and geomorphic surfaces

Soil mapping units

(Schaetzl and Anderson, 2005, p. 35)

O Horizon: surface accumulation of organic matter. Top layer is undecomposed and visible to the naked eye.

A Horizon: Mineral horizon that occurs under an O horizon or at the surface. The top A horizon contains accumulated organic matter and is typically dark. May have granular structure

E Horizon: Zone of eluviation of silicate clays, Fe, Al oxides. Pale in color and coarser due to leaching.

B Horizon: Zone of illuviation. Has little or no geologic structure. It may have illuvial accumulation of clays, aluminum, iron, salts, or humus. Structure may be blocky with coatings or gleying.

C Horizon: Weathered parent material, may have accumulation of carbonates

Soil pedon “a soil individual”

(Buol et al., 1980; Walker and Cohen, 2007)

Soil taxonomy and classification

System consists of 6 categories (#s in the U.S as of 2002)

Order (12)

Suborder (60)

Great groups (300)

Subgroups (2,400)

Families (5,500)

Series (17,000) [ie. county level soil mapping series]

(Walker and Cohen, 2007)

Distinguish features for distinguishing soil orders

(1) Composition of the soil (mineral vs. organic)

(2) Diagnostic horizons

(3) Distinctness of horizons

(4) Base saturation

(Walker and Cohen, 2007)

Soil orders common in the Midwest and major features Alfisols [alf] “forest soils” Subsurface horizons of silicate clay accumulation and moderate

to high base saturation. Humid climate with forest or prairie veg Entisols [ent] “recently formed” Little or no morphological development. This is due to

youth, dryness or cold, inertness of parent materials, or other factors that prevent soil horizon development.

Histosols [ist] “organic soils” Soils consisting largely of organic matter. These soils represent nonoxidizing, or water saturated conditions, such as the peat and muck in former bogs and ponds.

Inceptisols [ept] “embryonic soils” Soils with some diagnostic horizon or horizons, poorly expressed. A horizon is usually pale or dark gray, B horizon often red and bioturbated.

Mollisols [oll] “grassland soils” Soils with thick, dark surface horizons, moderate to high in organic matter, with a high base status. Characteristics of grasslands of steppes and prairies.

Spodosols [od] “subsoil sesquioxide” Soils with subsurface horizons of amorphous accumulations or of cementation with iron oxides. Moist sandy soil with pale gray, loose top horizon. Forest.

(Buol and others, 1980; Walker and Cohen, 2007)

Soil horizon nomenclature

(1) Use capital letters for master soil horizons (B = B horizon)

(2) Use suffixes to describe additional characteristics and features (Bs = B horizon with illuvial accumulation of sesquioxides)

(3) Use numerical prefixes to denote lithologic discontinuities (2Bs)

(4) Numerical suffixes denote subdivisions within a master horizon (Bt1, 2Bt2)

(5) The prime (‘) is used to indicate a 2nd occurrence of an identical horizon descriptor, but not for buried horizons (indicated by suffix “b”) or a lithologic change (denoted by numerical prefix).

(Walker and Cohen, 2007)

Entisols – new surfaces, beginning of soil development

i = slightly decomposed organic matter w = weak color or structure in the B horiz. t = illuvial accumulation of silicate clay

Images from www.geo.msu.edu/SoilProfiles

Lamellic Udipsamment A - Bw - E - E and Bt1 - E and Bt2 - BC Location: Southern Michigan, USA. Photo by R. Schaetzl. Tape increments 10 cm. Typic Udipsamment Oi - A - Bs - BC - C

Location: Central Lower Michigan, USA. Photo by R. Schaetzl

ud [L., udus, humid] = high moisture psamm [Gr., psammos, sand] = sandy texture

Inceptisol – weak horizonation

Images from www.geo.msu.edu/SoilProfiles

dystr [Gr., dys, ill; distrophic, infertile] = low base saturation, acidity problems likely

Spodic Dystrudept A - E - Bw - E/Bt - Bt/E - Bw'1 - Bw'2 - 2BC Location: Forest County, NE Wisconsin, USA. Photo by R. Schaetzl

Spodic Dystr-ud-ept

Order

Great group

Suborder Extragrade

formative

elements

Histosols -- wetlands

r = soft or weathered bedrock

Images from www.geo.msu.edu/SoilProfiles

sapr [Gr., sapro, rotten, dead, decaying] = having less than one-sixth (by volume) of the organic soil material consisting of recognizable plant tissue (after rubbing)

Lithic Haplosaprist Oi1 - Oi2 - 2Cr Location: Central Upper Michigan, USA. Photo by R. Schaetzl

Spodosols – evergreen forests, acidic, sandy

i = slightly decomposed organic matter a = highly decomposed organic matter h = illuvial accumulation of organic matter s = illuvial accumulation of sequioxides m = strongly cemented

Images from www.geo.msu.edu/SoilProfiles

hapl [Gr., haplous, simple] = minimum horizon development orth [Gr., orthos, true] = the common ones

Typic Haplorthod Oi - Oa - E - Bhs - Bsm - Bs - BC - C Location: Central Upper Michigan, USA. Photo by R. Schaetzl

Alfisols – Deciduous forest

Inceptic Hapludalf A - Bs - E - Bt1 - 2Bt2 - 3C Location: Eastern Lower Michigan, USA. Photo by R. Schaetzl

Inceptic Hapludalf A - E - Bs - E' - 2Bt1 - 2Bt2 - 2BC - 2C Location: NE Lower Michigan, USA. Tape increments 10 cm. Photo by R. Schaetzl

s = illuvial accumulation of sesquioxides t = illuvial accumulation of clay

Images from www.geo.msu.edu/SoilProfiles

hapl [Gr., haplous, simple] = minimum horizon development ud [L., udus, humid] = high moisture

Mollisols -- Prairies

w = weak color or structure t = illuvial accumulation of silicate clay

Images from www.geo.msu.edu/SoilProfiles

hapl [Gr., haplous, simple] = minimum horizon development ud [L., udus, humid] = of humid climate

Typic Hapludoll A - BA - Bw1 - Bw2 - Bw3 - Bt - R Location: Dodge County, SE Wisconsin, USA. Photo by R. Schaetzl

Soil Geomorphology and the Catena Concept

Figure 9.7 Schematic diagrams of soil-slope relations (Birkland, 1999)

Slope is stable

Slope is unstable

Field

~ 1839 land purchase Ipswich Prairie

Platte River – Galena River

Upland Drainage Divide,

SE Grant County, Wisconsin

Field

~1839 Land Purchase

Jim Knox photos

Southeast Grant County

Wisconsin Upland Sites

Approximately 38 cm

of topsoil erosion has

occurred during the

past 175 years of

agricultural land use.

(Source: Knox, 2001)

Severe rill erosion in late 19th century NW Illinois corn field. Photo Source: Wisconsin State Historical Society.

tree stump

(Buol et al., 1997)

Figure 6.29 Idealized changes in paleosol type and maturity with distance away from channel (Bridge, 2003)

Paleosols, Soil Geomorphology, and Floodplains

Example valley stratigraphic column Middle Fork Vermilion River near Armstrong, IL

(Stanke, 1988)

Web soil survey of Boardman area

http://websoilsurvey.nrcs.usda.gov/

Using soil mapping units for geomorphic interpretation and history (top 5 ft)

Web soil survey of Boardman area

http://websoilsurvey.nrcs.usda.gov/

Using soil mapping units for geomorphic interpretation and history (top 5 ft)

Lu = Lupton Muck

Tr = Tonkey-Hettinger-Pickford loam overwash

Ka = Kalkaska loamy sand

Soil series descriptions

Paleosols in alluvial settings

• Difficult to distinguish

• Overprinting with modern pedogenesis

• Muting from post-burial processes

• Indicators of paleoenvironments

• Look at on a landscape basis

• Represent periods of stability

• May have human artifacts

(Schaetzl and Anderson, 2005, p. 550)

Soil development and relative dating

Soil development or depositional unit?

Boardman River, Keystone Impoundment, Stop 2