Parent Material

Biota

Climate

Topography

Time

O horizon: accumulated organic layer at the soil surface. More organic matter than mineral matter. “Litter layer”

• A horizon: layer nearest the surface that is dominated by mineral particles, but has been darkened by the accumulation of organic matter. A horizons are often called “topsoil.”

• E horizon: The “leached and bleached” horizon, or zone of eluviation. E horizons are light colored, nearly white, due to the removal of clay, organic matter, and iron oxides.

• B horizons: form below O, A, and E horizons. The B horizon is the zone of accumulation, or illuviation.

• C horizon: unconsolidated material below the B horizon. Resembles the parent material but can be dug with a shovel. C horizons have not undergone sufficient soil forming processes to qualify as a B.

• R horizon: Consolidated rock. Little evidence of weathering. Bedrock.

• w –weak subsoil development
• t - accumulation of silicate cla
• g -strong gleying (loss of iron oxides, blue/gray color)
• k - accumulation of carbonates
• m - cementation or induration
• v – plinthite (accumulation of red iron-oxides, irreversible hardening)
• p - plowing or other disturbance (A horizon only)

• q - accumulation of silica
• r – weathered or soft bedrock (C horizon only)
• ss – slickensides (smeared clay films)

3 size types and sizes

made from?

Clay: <.002mm

Silt:.05mm-.002mm

sand: 2mm-.05mm

Soil Color

Causes of Color

Value: white to blackness in the color 0=black 10=white

Chroma: Intensity of color

Hue: color (blue, green etc)

Read Order

HVC

Iron oxides: Hematite is red (Fe2O3)
Goethite is yellow (FeOOH)
Organic Matter makes soil black and dark brown.

• Granular
• Platy
• Blocky: Angular Blocky and Subangular Blocky
• Prismatic and Columnar

• Structureless
– Massive (coherent mass with no aggregates or peds)
– Single-grain (e.g. beach sand)

Igneous rocks

Intrusive

Extrusive

formed when hot, molten magma cools.
– Intrusive (cools underground) - granite

Magma cools more slowly underground forming larger crystals
Granite = More Quartz (lighter, more resistant to weathering)
Gabbro = Less Quartz (Darker, less resistant to weathering)

– Extrusive-cools at the surface of the earth

Magma reaches the surface cooling faster forming smaller crystals
Rhyolite = More Quartz (lighter colored, more resistant to weathering)
Basalt = Less Quartz (darker colored, less

Primary minerals in igneous rocks: quartz, feldspars, biotite, hornblende, and olivine.

•Felsic Minerals: aluminum-rich.
– Potassium Feldspars
– Plagioclase Feldspars
– Muscovite mica

• Mafic Minerals: magnesium- and iron-rich.

– Olivine
– Pyroxene minerals
– Amphiboles
– Biotite mica

Resultant Soils

Sandstone

Shale

Limestone

Metamorphic Rocks

Sandstone ->

Limestone ->

Shale ->

Grantie ->

Categories of parent material:

How parent material got there

– Residuum or residual, rock weather in place

– Alluvium unconsolidated material deposited by rivers

– Lacustrine lake sediments, The parent material is clay and silt sized material, often organic-rich.

• Peat : slightly decomposed
• Muck : highly decomposed

– Colluvium deposited by gravity down slopes

Wind

• Eolian deposited sands by wind

•Loess - windblown silts and clay

– Marine ocean sediments

Glacial

• Till deposited by glaciers unsorted and compacted

•Outwash deposited by glaciers indistinguishable from other water deposts

– Organic accumulates in wetlands

volcanic ash soils

• Commonly found near volcanos
• Colloidal material is amorphous (allophane and ferrihydrite)
• Young soils (5000 – 10,000 years)
• High natural productivity except for phosphorus.

• Spodosols are acidic soils characterized by a subsurface accumulation of humus that is complexed with Al and Fe.

These photogenic soils typically form in coarse-textured parent material and have a light-colored

The process that forms these horizons is known as podzolization.

Spodosols often occur under coniferous forest in cool, moist climates.

• Hydric soils form under conditions of saturation

• Accumulation of iron and manganese nodules
• Zones of iron accumulation on pore surfaces and root channels
• Zones of iron depletion: gray mottles or gley colors

Organic matter decomposition rates are slow because of the lack of electron acceptors:
like oxygen

when water leaves life appears dramatically

Smooth

Wavy

Irregular

Broken

• An epipedon is a surface horizon. It may include both the A and B horizons if soil darkening extends from the surface into the B horizon.
• Eight different epipedons are recognized in soil taxonomy.

• Mollic epipedon - dark A horizon, high in organic matter. Value and Chroma 3 or lower when moist, Thick, dark, well-structured, pH>5.5

• Ochric epipedon – low O.M., light color

Subsurface Diagnostic Horizons

Argillic, Natric, Spodic, Cambic, Albic, Oxic

• Argillic: accumulation of silicate clay, clay films on ped surfaces (Bt horizon)
• Natric: Accumulation of sodium
• Spodic: Accumulation of Al- and Fe-oxides and humus.

• Cambic: Slightly altered horizon. Some evidence of illuvial process and structure development (Bw horizon).
• Albic: Elluvial horizon. Loss of Fe-oxides and silicate clays (E horizon).
• Oxic: Accumulation of Fe- and Al-oxides, and non-swelling silicate clays (kaolinite).

Soil Moisture Regimes

Aquic, Udic, Ustic, Xeric, Aridic, Torric

• The soil moisture regime is used to classify soils at the suborder level.

• Aquic – (wet, saturated soils)

• Udic – soils of humid climates (soil never dry more than 45 days: winter and summer rain)

• Ustic – soils of semi-arid climates (some summer rain)

• Xeric – soils of Mediterranean climates (winter rain)

• Aridic – soils of arid climates (deserts)

• Torric – hot and dry moisture regime

• Pergelic – permafrost

•Frigid - 0C to 8C, summer 6C> winter
• Cryic 0 to 8 oC mean annual soil temp.
• Mesic 8 to 15 oC
• Thermic 15 to 22 oC
• Hyperthermic >22 oC

How to read a map

ex:CbF2

Name of Description

First Letter: initial letter of the soil series name

Third Letter: Slope No letter = 0 A:low slope F:Steep

# = Erosion: 1 least 3 most

This is soil phase

Land Capability Classifications

Subclasses

e,w,s,c

For Agriculture

Classes 1-4 are good

4-8 bad

e: erosion

w: wet

s: shallow

c: bad climate

Al and Si Clays: Kaolinite = no swelling, Montmorillinite or smectite = swelling,

= dark brown/black

Al and Fe Clays: Gibbsite, Hematite = red

Limes: Calcite, Dolomite = white

Goethite - yellow

Phylosilicate Clays

Starting Material

• feldspar minerals, Al3+ is in tetrahedral coordination (surrounded by 4 oxygen atoms).
• During chemical weathering of primary the Al moves into octahedral coordination to form secondary

Clays are (-) charged

• Mica -

Muscovite (yellow mica) has Al in the octahedral sheet.

Biotite (black mica) has Fe in the octahedral sheet. => Vermiculite contains cations

Kandites have one sheet of tetrahedrally coordinated Si and one sheet of octahedrally coordinated Al. The layers are held together by H-bonding. 1:1 clay mineral.

There is no isomorphous substitution

2:1 clay mineral

Formed from the weathering of feldspar, mafic minerals, and volcanic ash in drier climates.

Swelling clay (vertisols)