The soil profiles and soil profile description soil pits road cuts other excavations
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What is a soil profile What is a soil horizon What is a soil layer Symbols for identifying and naming of soil horizons and layers Types of Soil Horizons. Master horizons Transitional horizons Subordinate horizons and symbols.

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The Soil Profiles and Soil Profile Description (Soil pits, Road cuts, Other excavations)

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The soil profiles and soil profile description soil pits road cuts other excavations

What is a soil profile

What is a soil horizon

What is a soil layer

Symbols for identifying and naming of soil horizons and layers

Types of Soil Horizons.

Master horizons

Transitional horizons

Subordinate horizons and symbols

The Soil Profiles and Soil Profile Description(Soil pits, Road cuts, Other excavations)


Soil profile showing soil horizons

Soil Profile Showing Soil Horizons

  • Soil profile is a vertical section of soil from the earth’s surface extending to the parent material that shows the individual horizons of the soil.

  • Soil horizon is a layer of soil approximately parallel to the soil surface with distinct characteristics produced by soil forming processes

  • Soil Layer is a layer in the soil deposited by a geologic force (wind, water, glaciers, oceans, etc.) and not relating to soil forming process.


How do you start describing the soil

How do you start describing the soil?

What do you see?

What is different from top to bottom?

How deep do roots go?


Identification and nomenclature of soil horizons

Oe

Oa

A

E

Soil Profile 1

Soil Profile #2

Bt1

O

Bt2

A

BC

E

C

B

R

C

R

Identification and Nomenclature of Soil Horizons

  • In making soil examinations, every horizon or layer is described separately.

  • Three kinds of symbols are used in various combinations to designate horizons and layers. They are:

    • Capital letters

    • Lower case letters

    • Arabic numerals


The soil profiles and soil profile description soil pits road cuts other excavations

O

A

E

B

C

R

Oe

Oa

A

E

Bt1

Bt2

BC

C

R

Horizon Designations

Soil Profile #1

  • Capital letters are used to designate the master horizons and layers.

  • Lower case letters are used (as suffixes) to indicate specific characteristics of the master horizon and layer.

  • Arabic numerals are used (as suffixes) to indicate vertical subdivisions within a master horizon or layer and (prefixes) to indicate lithological discontinuities.

Soil Profile #2


Types of horizons 1 master horizons

O

A

E

B

C

R

Types of Horizons1. Master Horizons

  • The capital letters O, A, E, B, C, and R represent the master horizons and layers of soil.

  • The capital letters are the base symbols to which other characters are added to complete the designations.


The soil profiles and soil profile description soil pits road cuts other excavations

Top Soil

Subsoil

Parent Material


The soil profiles and soil profile description soil pits road cuts other excavations

A Horizon

B Horizon

C Horizon


O horizons or layers organic soil horizon

O

A

E

B

C

R

O Horizons or Layers(Organic Soil Horizon)

  • Layers dominated by organic material

  • Identification Criteria

    • >20% organic matter

    • Dark color (

    • Feels ‘Squishy”

    • Identifiable dead leaves, grass, etc. accumulated at surface


A horizons

O

A

E

B

C

R

A Horizons

  • Referred to as topsoil

  • Typically ranging from 6-30 centimeters thick

  • Mineral horizon formed at the surface or below an O horizon.

  • Characterized by an accumulation of well decomposed organic matter intimately mixed with the mineral fraction.

  • Identification Criteria

    • Mineral soil material

    • Mix of well decomposed organic matter and mineral material

    • Surface mineral horizon

    • Typically dark in color-darker than underlying horizons


The soil profiles and soil profile description soil pits road cuts other excavations

A-Horizon

A-Horizon


E horizons

O

A

E

B

C

R

E Horizons

  • Mineral horizon in the upper part of the soil typically underlying an O or A horizon.

  • Light colored, leached horizons ranging from not being present to several centimeters thick

  • Light color due to the natural color of the mineral grains.

  • Formed by weak organic acids that strip coatings from mineral grains.

  • Field Identification

    • Zone of eluviation - removal of clays, Fe, Al, and humus

    • Lighter in color than over or underlying horizon

    • Near surface, below O or A horizons and above a B horizon


The soil profiles and soil profile description soil pits road cuts other excavations

E Horizon

E Horizon


B horizons

O

A

E

B

C

R

B Horizons

  • Referred to as subsoil.

  • Horizons that formed below an O, A, or E horizon and that have undergone changes during soil formation such that the original parent material structure is no longer discernable. Some of the changes are brought about by materials accumulating in the following ways:

  • The zone of accumulation (or illuviation) within the soil.

  • Field Identification

    • Subsurface horizon formed below an O, A, E horizon and above the C horizon

    • Formed as a result of soil forming processes

    • Expressed often by color

    • Illuvial concentration-zone of accumulation

      • (silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica) alone or in combination;


The soil profiles and soil profile description soil pits road cuts other excavations

B Horizon

B Horizon


C horizons or layers

O

A

E

B

C

R

C Horizons or Layers

  • Referred to as parent material.

  • These horizons and layers are little affected by soil forming processes (unweathered geologic material).

  • Field Identification

    • Little affected by soil-forming processes

    • Geologic layering

    • Color of unweathered geologic material


R layers

O

A

E

B

C

R

R Layers

  • Hard bedrock

  • E.g. granite, sandstone, basalt, quartzite, and indurated limestone.

  • Field Criteria

    • Can not dig it with a shovel or backhoe


The soil profiles and soil profile description soil pits road cuts other excavations

A-Horizon

E-Horizon

B-Horizon

C-Horizon


Types of horizons 2 transitional horizons

O

A

E

EB

B

BC

C

R

Types of Horizons2. Transitional Horizons

  • Horizons dominated by properties of one master horizon but having subordinate properties of another

  • Two capital letter symbols are used as EB, BE, BC.

  • Master horizon that is given first designates the kind of horizon whose properties dominate the transitional horizon

  • E.g. EB has characteristics of both an overlying E and an underlying B horizons, but is more like E than B.


The soil profiles and soil profile description soil pits road cuts other excavations

A Horizon

A/B Horizon

B Horizon


Types of horizons 3 subordinate horizons distinctions within master horizons and layers

Oe

Oa

A

E

Bt

Btg

BC

C

R

Types of Horizons3. Subordinate Horizons(Distinctions within master horizons and layers)

Lower case letters are used as suffixes to designate specific kinds of master horizons and layers.

E.g. a B horizon which has illuvial accumulation of clay is designated Bt.

A Bt horizon which shows evidence of gleying (water saturation) is designated as Btg.

The lower case letters t and g indicate clay accumulation and gleying respectively. (See next slide for symbols and their meanings)


The soil profiles and soil profile description soil pits road cuts other excavations

Forest Floor

O-Horizon

A-Horizon

E-Horizon

B-Horizon


The soil profiles and soil profile description soil pits road cuts other excavations

Typical Forest Soil

Typical Grassland Soil


Soil profile described

Soil Profile Described


The soil profiles and soil profile description soil pits road cuts other excavations

a - sapric - organic soils - well decomposed (O-Horizon)

b - buried soil horizon (A-, B-Horizon)

d - dense - geogenic soil material (B-Horizon)

e - hemic - mod. decomp. - organic soil (O-Horizon)

f - frozen soil - permanently frozen, permafrost (A-, B-, C-Horizon)

g - gleyed soil - gray color due to low O2 - reduction of Fe (B-Horizon)

h - accumulation of humus other than in the A or O horizons (B-Horizon)

i - fibric - organic - non-decomposed (O-Horizon)

k - accumulation of calcium carbonate (CaCO3) (B-, C-Horizon)

m - cementation - hard - indurated (B-Horizon)

n- sodium accumulation (B-Horizon)

p- plowing (A-Horizon)

q - silica accumulation - very weathered or old soil (B-Horizon)

r - soft rock (C-Horizon)

s - sesquioxides - accumulation of Fe and Al - red color (B-Horizon)

t - clay accumulation (B-Horizon)

w - color or structure development (B-Horizon)

x - Fragipan - hard, dense layer that developed with time (B-Horizon)

y - gypsum accumulation (CaSO4) (B-, C-Horizon)

z - salts more soluble than gypsum (KCL - NaCl - NaSO4) (B-, C-Horizon)


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