Transcript The Soil Profile - AAMU Myspace Login

The Soil Profiles and Soil
Profile Description
(Soil pits, Road cuts, Other excavations)
1. What is a soil profile
2. What is a soil horizon
3. What is a soil layer
4. Symbols for identifying and naming of soil
horizons and layers
5. Types of Soil Horizons.
– Master horizons
– Transitional horizons
– Subordinate horizons and symbols
Soil Profile Showing Soil
Horizons
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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?
What do you see?
What is different from top to
bottom?
How deep do roots go?
Identification and Nomenclature
of Soil Horizons
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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
Soil Profile 1
O
A
E
Soil Profile #2
Oe
Oa
A
E
Bt1
B
Bt2
BC
C
C
R
R
Horizon Designations
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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 #1
O
A
E
B
C
R
Soil Profile #2
Oe
Oa
A
E
Bt1
Bt2
BC
C
R
Types of Horizons
1. Master Horizons
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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.
O
A
E
B
C
R
Top Soil
Subsoil
Parent
A Horizon
B Horizon
C Horizon
O Horizons or Layers
(Organic Soil Horizon)
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Layers dominated by organic
material
Identification Criteria
–
–
–
–
>20% organic matter
Dark color (
Feels ‘Squishy”
Identifiable dead leaves, grass, etc.
accumulated at surface
O
A
E
B
C
R
A Horizons
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Referred to as topsoil
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Typically ranging from 6-30 centimeters thick
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Mineral horizon formed at the surface or below an
O horizon.
O
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Characterized by an accumulation of well
decomposed organic matter intimately mixed with
the mineral fraction.
A
E
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Identification Criteria
B
– Mineral soil material
– Mix of well decomposed organic matter and mineral
material
– Surface mineral horizon
– Typically dark in color-darker than underlying
horizons
C
R
A-Horizon
A-Horizon
E Horizons
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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
O
A
E
B
C
R
E Horizon
E Horizon
B Horizons
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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
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(silicate clay, iron, aluminum, humus, carbonates, gypsum, or
silica) alone or in combination;
O
A
E
B
C
R
B Horizon
B Horizon
C Horizons or Layers
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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
O
A
E
B
C
R
R Layers
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Hard bedrock
O
E.g. granite, sandstone,
basalt, quartzite, and
indurated limestone.
A
E
Field Criteria
C
– Can not dig it with a
shovel or backhoe
B
R
A-Horizon
E-Horizon
B-Horizon
C-Horizon
Types of Horizons
2. Transitional Horizons
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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.
O
A
E
EB
B
BC
C
R
A Horizon
A/B Horizon
B Horizon
Types of Horizons
3. 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)
Oe
Oa
A
E
Bt
Btg
BC
C
R
O-Horizon
A-Horizon
E-Horizon
B-Horizon
Forest Floor
Typical Forest Soil
Typical Grassland Soil
Soil Profile Described
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 (BHorizon)
i - fibric - organic - nondecomposed (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)