Transcript The Soil Profile - AAMU Myspace Login

The Soil Profile
• 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
• Therefore, a soil profile is made up of soil
horizons.
• It is this soil profile that is studied in the
field to represent a bigger area.
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
• 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 both as suffixes to
indicate vertical subdivisions within a
horizon or layer and prefixes to indicate
lithological discontinuities.
1. Master Horizons and Layers
• 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.
Soil profile showing major horizons
O Horizons or Layers
(Organic Soil Horizon)
• Layers dominated by organic material
• Some are saturated with water for long
periods of time or were once saturated but
are now artificially drained.
A Horizons
• Mineral horizons that formed at the surface or
below an O horizon and
– 1) are characterized by an accumulation of humified
organic matter intimately mixed with the mineral
fraction
– 2) have properties resulting from cultivation,
pasturing, or similar kinds of disturbance.
– 3) Usually coarser in texture having lost some of its
finer materials by translocation or erosion
E Horizons
• Mineral horizon in which the main feature
is loss of silicate clay, iron, aluminum, or
some combination of these, leaving a
concentration of sand and silt particles of
quartz or other resistant minerals.
• E horizons are usually, but not necessarily,
lighter in color than an underlying B
horizon.
B Horizons
• Horizons that formed below an A, E, or O
horizon and are dominated by obliteration
of all or much of the original rock structure
and by the following:
– illuvial concentration of silicate clay, iron,
aluminum, humus, carbonates, gypsum, or
silica, alone or in combination;
– evidence of removal of carbonates
– residual concentration of sesquioxides;
– coatings of sesquioxides that make the horizon
lower in color value, higher in chroma, or
redder in the hue than overlying and
underlying horizons;
– alteration that forms silicate clay or liberates
oxides or both and that forms granular, blocky,
or prismatic structure;
– Any combination of these.
C Horizons or Layers
• Horizons or layers excluding hard bedrock,
that are little affected by pedogenic
processes and properties of O, A, E, or B
horizons.
• The material of C horizons may be either
like or unlike that from which the solum
presumably formed.
R Layers
• Hard bedrock
• E.g. granite, sandstone, basalt, quartzite,
and indurated limestone.
2. 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.
• Major pedogenic subdivisions within O, A,
and B horizons of mineral soils are
indicated by a primary Arabic number e.g.
O1, O2, B1, B2 etc.
• Designations of common subdivisions of
soil horizons are as follows;
• Oi, Oe, Oa, A, E, AB, E/B, AC, BA, BE,
B/E, BC, CB, B, Bw.
3. Subordinate 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 is permanently
frozen is designated Bf. The lower case letter f
indicates frozen horizon. The symbols and their
meanings are as follows:
a - sapric - organic soils - well
decomposed
b - buried soil horizon
d - dense - geogenic soil material
e - hemic - mod. decomp. - organic
soil
f - frozen soil - permanently frozen,
permafrost
g - gleyed soil - gray color due to
low O2 - reduction of Fe
h - accumulation of humus other
than in the A or O horizons
i - fibric - organic - nondecomposed
k - accumulation of calcium
carbonate (CaCO3)
m - cementation - hard - indurated
n - sodium accumulation
p - plowing - only used with A
q - silica accumulation - very
weathered or old soil
r - soft rock - used with C or Cr
s - sesquioxides - accumulation of
Fe and Al - red color
t - clay accumulation - clay films
w - color or structure development
x - Fragipan - hard, dense layer
that developed with time
y - gypsum accumulation (CaSO4)
z - salts more soluble than gypsum
(KCL - NaCl - NaSO4)