SOIL PROFILE
Dr. S. Ibrahim Abro
Associate professor
Soil and environment
05/05/202 1
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Soil
Major part of the natural
environment,
Vital to the existence of life on the
planet.
Soil is the result of the process of the
gradual breakdown of rock, such as
weathering and erosion
Soil is made up from four
constituents:
mineral material,
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organic material,
Soil Profile
The soil profile is one of the most important
concepts in soil science.
The soil profile is defined as a vertical section
of the soil that is exposed when a soil pit, or
hole, is dug from the surface of the soil to the
underlying bedrock.
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Soil
Structure
Combination or arrangement of primary soil
particles.
Soil particles are:
Sand
Silt
Clay
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Cont,,
Sand: Natural occurring rough material,
The size of sand particles range between 2.0 mm and 0.05
mm.
Silt: Small particles, and size is between sand and clay.
Silt size as 0.05 mm and 0.002 mm.
Clay: very fine particles
And clay, less than 0.002 mm.
Notice that clay particles may be over one thousand times
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smaller than sand particles.
Soil
Composition
Soil composition is an
important aspect of nutrient
management.
The basic components of soil
are:
Minerals/Nutrients 45%,
Organic matter 5%,
Water 25% and
Air 25%. 7
Factors of
Formation
Soil is formed by…
Parent Material: the original soil transported
from elsewhere, usually by wind or water, at
different speeds
Climate: the amount, intensity, timing, and
kind of precipitation that breaks down parts of
ecosystem (i.e. rocks, trees) into soil
Topography: Slope and Aspect affect the angle
of the land.
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Cont,,
Biological: Plants,
animals, microscopic
organisms, and humans
interact with soil in
different ways.
Time: the amount of time
it takes for the four
factors (above) to
interact with each other.
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Soil Colour
Two types of soil on the basis of colour
1) Dark Colour Soil
2) Light Colour Soil
1.Dark Colour Soil:
Rich with a lot of organic matters.
2. Light Colour Soil:
Not so rich with organic matters
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Components of the Soil
Profile
A soil horizon makes up a distinct layer of soil.
The soil profile extends from the soil surface to
the parent rock material.
The regolith includes all of the weathered
material within the profile. The regolith has two
components:
Solum
Saprolite.
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Cont,,
Solum Saprolite
The saprolite is the least
The solum includes the
upper horizons with the weathered portion that
most weathered portion lies directly above the
solid, parental bedrock
of the profile.
C Horizon
Surface and subsoil
layers.
O, A and B Horizons. 12
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Master Horizons
Horizons based on color, roots, structure, rock
fragments.
Master Soil Horizons are depicted by a capital
letter in the order (from top to down):
The master horizons are represented by the
letters: B Horizon
O Horizon C Horizon
A Horizon R Horizon 14
E Horizon
O Horizon
Surface horizon that is comprised of organic
material at various stages of decomposition.
Surface-layer, at depths of 0-2 feet.
Dark in color, soft in texture.
Leaf litter – leaves, needles, twigs, moss,
lichens that are not decomposing.
Humus - rich organic material of plant and
animal origin in a stage of decomposition 15
A
Horizon
“Topsoil” or “Biomantle” Horizon.
largely consists of minerals (sand, silt, and clay)
Topmost layer of mineral soil, at depths of 2-10 feet.
Some humus present, darker in color than layers
below.
Biomantle - most biological productive layer;
earthworms, fungi, and bacteria live this layer.
Smallest and finest soil particles.
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E Horizon
The “Leaching Layer” Horizon
Small layer between A & B horizons
At depths of 10-15 feet
Light in color, mainly sand & silt
Poor mineral and clay content due to leaching –
the loss of water-retaining plant nutrients to
the water table
Soil particles larger than in A horizon but
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smaller than in B horizon.
B
Horizon
The “Subsoil” Horizon.
At depths of 10-30 feet.
Rich in clay and minerals like Fe & Al.
Some organic material may reach here
through leaching.
Plant roots can extend into this layer
Red/brown in color due to oxides of Fe &
clay. 18
C Horizon
The “Saprolite” Horizon.
At depths of 30-48 feet.
Made up of large rocks or lumps of partially
broken bedrock.
Least affected by weathering and have
changed the least since their origin.
Devoid of organic matter due to it being so far
down in the soil profile.
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R
Horizon
The “Bedrock” Horizon.
At depths of 48+ feet.
Deepest soil horizon in the soil profile.
Continuous mass of bedrock.
Colors are those of the original rock of the
area.
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Cont,,
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THE
END
THANK YOU
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