Download AG-NL-01.470-05.1p Envirothon_soil_Introduction

An Introduction to Soil
Bryan McElvany
Research Coordinator
Warnell School of Forest Resources
Patrick Davies
August 2008
@%*!
Your first dirty word for the day
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@%*T
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@I*T
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@IRT
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DIRT
This is the stuff under your
fingernails
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Why is soil science intimidating?
• Whole new vocabulary
• Hard to visualize
• Somewhat complex topics like chemistry
and physics
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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).
2) Traditional definition: Material which
nourishes and supports growing plants
(includes rocks, water, organic material,
air).
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What is soil made of?
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•
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Mineral Matter
Organic Matter
Air
Water
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What is the function of soil?
• Plant medium
• Recycling system for
nutrients
• Animal home
• Engineering medium
• System for water
supply and
purification
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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.
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Soil Formation Factors
•
1)
2)
3)
4)
5)
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There are five main factors that influence
soil formation processes.
Type of Parent Material
Climate
Topography
Biotic Components
Time
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Parent Material
• Two major divisions in type of parent material
1) Residual-Formed in place (Residuum)
2) 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
• 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.
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Soil Formation Processes
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Soil Formation in Action
• 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:
– 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?
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Soil Horizons
• 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.
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O Horizon
• 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
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A Horizon
• 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
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E Horizon
• 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
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B Horizon
• 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
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C Horizon
• Parent material
• The unconsolidated
material that has
been affected little by
the soil forming
processes
O
A
E
B
C
R
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Soil Texture
• 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
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Soil Texture
• 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.
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Soil Texture
• 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.
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Soil Structure
• Soil structure is the
arrangement of soil
particles into
aggregates.
• Structureless soils
do occur as either
single grained or
massive.
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Granular
Blocky
(Subangular)
(Angular)
Prismatic
Columnar
Platy
Wedge
Pore Space
• 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.
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Soil Permeability
• 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.
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Soil Texture and Permeability
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Soil Structure -Permeability
Granular
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Blocky
Platy
Soil Water
• 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.
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Soil Water
• 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.
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Soil Water
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Available Water Capacity
• 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.
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Available Water Capacity
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The End
Thanks
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