Download What is soil? - Central Senior High School

An Introduction to Soil
Bryan McElvany
Research Coordinator
Warnell School of Forest Resources
Patrick Davies
@%*!
Your first dirty word for the day
@%*T
@I*T
@IRT
DIRT
This is the stuff under your
fingernails
Why is soil science intimidating?
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Whole new vocabulary
Hard to visualize
Somewhat complex topics like chemistry and
physics
What is soil?
Several different ways to define soil
1) Geologic definition: Loose surface of the
earth as distinguished from solid bedrock
(support of plant life not required).
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2) Traditional definition: Material which
nourishes and supports growing plants
(includes rocks, water, organic material, air).
What is soil made of?
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Mineral Matter
Organic Matter
Air
Water
What is the function of soil?
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Plant medium
Recycling system for
nutrients
Animal home
Engineering medium
System for water
supply and purification
The ability of soil to perform those
functions is dependant upon:
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Soil Texture
Soil Structure
Soil Chemistry
Soil Age
Site Factors (topography, water, etc)
Etc.
Soil Formation Factors
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1)
2)
3)
4)
5)
There are five main factors that influence soil
formation processes.
Type of Parent Material
Climate
Topography
Biotic Components
Time
Parent Material
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1)
2)
Two major divisions in type of parent material
Residual-Formed in place (Residuum)
Transported-Parent material was moved by:
- wind (Eolian)
- ice (Glacial)
- gravity (Colluvial)
- water:
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rivers (Alluvial)
oceans (Marine)
lakes (Lacustrine)
Soil Formation Processes
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Transformations – modification of soil constituents.
Mineral weathering, organic matter breakdown.
Translocations – movement up, down, or laterally of
soil constituents.
Additions – movement of soil material in from
outside sources. Organic material from leaves, dust
from atmosphere.
Losses – movement of soil material out of the soil.
Transportation to groundwater, erosion of surface
materials.
Soil Formation Processes
Soil Formation in Action
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The soil formation processes, operating under the
influence of the soil formation factors, is the driving
force in soil genesis.
Important questions to remember are:
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What transformations and translocations took place in the
parent material to form this soil?
What materials were removed?
What was added?
How did the climate and topography affect those processes
over time?
Soil Horizons
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As soils develop they form layers called Horizons.
These horizons have distinct characteristics produced
by soil forming processes.
Master horizons include the O, A, E, B, and C
horizons.
Not every soil contains every horizon based on the
level of development of the soil.
Depth of each horizon varies between different soils.
O Horizon
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Layer of accumulated
organic matter such as
leaves, grass, twigs
Material can be in
various states of
decomposition
Generally dark in color
O
A
E
B
C
R
A Horizon
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Zone of incorporation of
organic matter into the
mineral soil
Generally it’s the most
productive horizon
High biological activity
Generally dark in color
Topsoil
O
A
E
B
C
R
E Horizon
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Zone of Eluviation or
leaching
Eluviation is the movement
of soil material out of a
layer of soil
Soluble minerals and
organic material move out
of this horizon
Generally a lighter
“washed” appearance in
color
O
A
E
B
C
R
B Horizon
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Zone of illuviation or
deposition
Accumulation of materials
“washed” from horizons
above
This material is commonly
clay, humus, sesquioxides,
or a mixture of the three
Variable in color from reds
and yellows to browns and
grays
O
A
E
B
C
R
C Horizon
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Parent material
The unconsolidated
material that has been
affected little by the soil
forming processes
O
A
E
B
C
R
Soil Texture
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Soil Texture is the relative proportion of the primary
particles in the soil.
Sand = 2mm – 0.05mm
Silt = 0.05mm – 0.002mm
Clay = < 0.002mm
Soil Texture
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This proportion of
sand, silt, and clay
can be grouped into
textural classes.
Soil texture has a
great deal to do with
many other soil
characteristics.
Soil Texture
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Coarse textured soil – soil that has a higher
proportion of larger particles. Sand, Loamy
sand, Sandy loam.
Fine textured soil – soil that has a higher
proportion of smaller particles. Clay, Silty
clay, sandy clay.
Soil Structure
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Soil structure is the
arrangement of soil
particles into
aggregates.
Structureless soils do
occur as either single
grained or massive.
Granular
Blocky
(Subangular)
(Angular)
Prismatic
Columnar
Platy
Wedge
Pore Space
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The voids between soil particles are called pores.
These can either be filled with water or air.
Soil texture plays a major role in total pore space as
well as size of pores.
Coarse textured soils (sandy) have larger pores, but
less total pore space.
Fine textured soils (clayey) have smaller pores, but
more total pore space.
Soil Permeability
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Permeability is a measure of how fast air and
water can move through a soil.
Soil texture and soil structure both pay a role
in soil permeability.
Soil Texture and Permeability
Soil Structure -Permeability
Granular Blocky
Platy
Soil Water
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Saturated soil is when that soils pores are full of
water.
Gravitational water is that water that moves out of the
soil due to gravity. This water is generally in the
larger Macro-pores.
Capillary water is that water that is held in the soil
due to adhesion and cohesion against the pull of
gravity. This water is generally held in the smaller
Micro-pores and as a film around soil particles.
Soil Water
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After a major rain event, once the gravitational
water has left the soil, the soil is at Field
Moisture Capacity.
The wilting point is reached when soil water
levels decline to the point that all remaining
water is held too tightly by soil particles to be
removed by the plant.
Soil Water
Available Water Capacity
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Available water capacity is a measure of the
water available to plants.
Commonly defined as the difference between
the amount of water at field moisture capacity
and the amount at the wilting point.
This is the water a plant has a chance of
utilizing.
Available Water Capacity
The End
Thanks