Soil 101 Everything you need to know!

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Transcript Soil 101 Everything you need to know!

Soil 101
Everything you need to
Ms. Brown
Part 2: Understanding Soil Formation
Identify five factors involved in soil
Parent material: Type of rock material the soil
is formed from.
Climate: Temperature and moisture
characteristics of the area in which the soil
was formed.
Living organisms: The organisms, including
plant material, that live within the soil.
Topography: Slope characteristics of the soil
Time or weathering: Age of the soil and its
Types of Parent Material
• Parent materials are formed by the
disintegration and decomposition of rock.
• They are classified according to the way they
were moved and scattered.
Types of Parent Material
occurred from the blowing of the soil after the glaciers melted
and dried. well-balanced mineral content, medium texture, and
excellent water-holding capacity, Most Desirable Parent Material
occurred when the glaciers melted.
The melt waters carried the gravelly materials away to be
deposited below the glacial ridges.
Sandy outwash was carried further downstream and the finer
materials, silt and clay, were deposited in lakebeds or slow
moving water along streams.
variety of sizes of soil particles.
These soil particles have not been layered from the effects of
wind or water
recent sediments deposited by streams as they flood.
Alluvium is generally a water-borne material deposited on
Bed Rock
• Bedrock most of the shale, sandstone, or
limestone bedrock is buried by loess, glacial
till, outwash, or alluvium.
• However, in the unglaciated areas weathered
bedrock has provided soil parent material.
Organic Matter
• Organic matter: Organic soils occur
where formerly shallow ponds supported
swamp vegetation.
– The wet conditions slowed decay of the
dead plants so that organic matter could
– The two types of organic soils are referred
to as peat and muck.
– Muck is more decomposed than peat
How Topography Affects Soil
• Topography refers to the slope characteristics
of a soil.
• It includes the degree or steepness, length,
shape, and direction of a slope.
• These factors influence the amount of
rainwater runoff, or the amount that enters
the soil or collects in small depressions on the
soil surface.
• Soils on steep slopes have higher amounts of
runoff and erosion than those on level
How Organisms Affect Soil
• Two types of native vegetation:
– tall prairie grass --- prairie soils
– deciduous-hardwood forests--timber soils.
• Prairie soils have a dark and deep surface layer.
• This is because roots from the prairie grass filled
the top of the soil to a depth of 1 to 2 feet or
• Partial decay of these roots over a long period of
time gave these soils a high organic matter
How Organisms Affect Soil
• Timber soils tend to have a thin, moderately dark layer.
• This is due to organic matter accumulating on the
surface where decay occurs more rapidly.
– When tilled, this dark material is mixed with the soil below to
produce a lighter color.
• Other living matter that influences the development of
soil includes various kinds of animal life.
• Earthworms, crawfish, ground squirrels and other
burrowing animals, and various insects which
incorporate organic matter into the soil are examples.
Types of Weathering
Chemical Weather
Physical Weathering
Chemical weathering changes
the chemical makeup of rock
and breaks it down.
Rainwater is mildly acidic, and
can slowly dissolve many soil
Some minerals react with
oxygen in the atmosphere.
Oxidation further acts to
decompose rock.
Physical weathering the effects
of climatic factors such as
temperature, water, and wind.
Freezing and thawing is a major
contributor to physical
• Weathering causes soil to:
–Develop rapidly, plant nutrients are
released, and organic matter
• Soils will develop faster in humid
regions than in arid regions.
– Mature soil is at peak productivity with a high
amount of organic matter.
• Water begins leaching away nutrients and plant growth
starts to decline.
• This results in less organic matter.
– Minerals continue to break down and clay is
leached into the subsoil.
• The soil becomes lighter in color from less organic
How Climate Affects Soil Development
• Climate refers to rainfall, freezing, thawing,
wind, and sunlight.
– These factors are either directly or indirectly
responsible for the breakdown of rocks and
minerals, the release of plant nutrients, and many
other processes affecting the development of
What is Soil Texture?
• Soil texture is the fineness or coarseness of a
• It describes the proportion of three sizes of
soil particles. These are:
– Sand - large particle
– Silt - medium sized particle
– Clay - small particle
What does Texture Affect?
• Soil workability the ease with which soil may
be tilled and the timing of working the soil
after a rain
• Ability of plants to grow some root crops like
carrots and onions will have difficulty growing
in a fine-textured soil
Determining Soil Texture
• Soil texture may be determined in one of two
– The percentages of sand, silt, and clay may be
tested in the lab.
• Once tested, you may determine the textural class of
the soil by referring to the textural triangle.
– The ribbon method.
and Size
of the
Textural Triangle
Understanding the
Textural Triangle
and Determining
Soil Texture
Worksheet: Part 1
• Determining Soil Texture by the Ribbon
Soil Profiles
What is a Soil Profile?
• A soil profile is a vertical cross-section of the soil.
– When exposed, various layers of soil should be apparent.
• Each layer of soil may be different from the rest in
a physical or chemical way.
– The differences are developed from the interaction
of such soil-forming factors as:
Parent material
Weathering (time)
Native vegetation
A soil profile is
usually studied to a
depth of 3 to 5
What are the major horizons of a soil
profile and how do they differ?
• There are 3 primary soil horizons called
master horizons.
– A Horizon
– B Horizon
– C Horizon
A Horizon.
This is often referred to as
topsoil and is the surface
layer where organic matter
Over time, this layer loses
clay, iron, and other
materials due to leaching.
This is called eluviation.
The A horizon provides the
best environment for the
growth of plant roots,
microorganisms, and other
• O Horizon.
– This is an organic
layer made up of
partially decayed
plant and animal
– It generally occurs in
undisturbed soil
such as in a forest.
B Horizon.
This horizon is
referred to as the
It is often called the
“zone of
accumulation” since
chemicals leached
from the A and E
accumulate here.
• E Horizon.
• This is the zone of
greatest eluviation.
– Because the clay,
chemicals, and
organic matter are
very leached, the
color of the E
horizon is very light.
– It usually occurs in
sandy forest soils
with high amounts
of rainfall.
B Horizon
– This accumulation is called illuviation. The B
horizon will have less organic matter and more
clay than the A horizon.
– Together, the A, E, and B horizons are known as
the solum.
– This is where most of the plant roots grow.
C Horizon
• This horizon is referred to as the substratum.
– It lacks the properties of the A and B horizons
since it is influenced less by the soil forming
– It is usually the parent material of the soil.
R Horizon
• This is the underlying bedrock, such as
limestone, sandstone, or granite.
– It is found beneath the C horizon.
Soil Profile Horizons
• O Horizon
A Horizon
B Horizon
C Horizon
R Horizon
organic layer of leaves,
roots,and decaying material
Bedrock or solid rock
below the C Horizon
How do soils within a soil profile
change over time?
• Soils change over time in response to their
• The environment is influenced by the soilforming factors.
The causes of these changes can be
classified into 4 processes:
– Additions. Materials such as fallen leaves, wind-blown
dust, or chemicals from air pollution that may be added
to the soil.
– Losses. Materials may be lost from the soil as a result of
deep leaching or erosion from the surface.
– Translocations. Materials may be moved within the soil.
• This can occur with deeper leaching into the soil or upward
movement caused by evaporating water
– Transformations. Materials may be altered in the soil.
• Examples include organic matter decay, weathering of
minerals to smaller particles, or chemical reactions.
Understanding Soil Color
• What are physical features used to
differentiate between soils?
– Texture coarseness or fineness of soil
– Structure the way in which soil particles are
held together
– Depth of horizons the depth of each soil
– Color refers to the darkness or lightness of
the soil color
What are the colors used to describe
surface soils?
• Colors associated with surface soils are
dependent on the amount of organic
matter found in them.
• Colors may be classified as:
– Very Dark: approximately 5% organic matter
– Dark approximately 3.5% organic matter
– Moderately dark approximately 2.5% organic
– Light approximately 2% organic matter
– Very light approximately 1.5% organic matter
The amount of organic
matter is the factor used to
determine the color of the
surface soil.
The amount of organic
matter is determined by the
kind of native vegetation.
Native vegetation refers to
the type of plant material that
grew on the soil.
What colors are used to describe
• Subsoil colors are associated with natural
drainage of the soils.
• This is the drainage condition that existed
when the soil was forming.
• Subsoil colors are classified as:
– Bright-colored brown, reddish brown, or
yellowish brown
– Dull-colored gray or olive gray
– Mottle-colored clumps of both bright and dull
colors mixed together
What factors determine the color of subsoil?
• The color of subsoil is determined by the status of
iron compounds.
• These are determined by the type of drainage
found in the soil as it formed. Good drainage
provides subsoil that is bright in color.
• This is because the iron found in these soils has
been oxidized.
• This can be compared to metal that oxidizes or
rusts when both moisture and air are present.
• Rust has a bright or orange color.
What factors determine the color of
• Poor drainage provides subsoil that is dull or
gray in color.
• This is because the iron found in those soils
has not been subject to air or oxygen.
• The iron compounds do not oxidize.
• This leaves a grayish color.
What factors determine the color of
• Somewhat poor drainage provides subsoils
that are mottled.
• This is because the soil was saturated with
moisture for certain periods.
• This leaves a gray color in some soil clumps.
• Since the soil was comparatively dry during
other periods, it left a bright color in other soil
How do parent material, age, and
slope affect the color of soil?
• In addition to organic matter and drainage,
soil color may also be affected by other
– parent material
– age
– slope
As soils age, much of the
darker color is lost due to the
weathering process.
This causes the soil to lose
organic matter.
Soil on top of hills is usually
lighter in color than the soil in
depressions or on level
This is partly due to the darker
topsoil being washed off the
This leaves the lighter
subsurface or subsoil exposed.
Parent Material
• The color of a soil is
associated with the
kind of material
from which it is
• Soils that are
developed from
sand or lightcolored rock will be
• Those developed
from darker
materials such as
peat or muck, will
be darker in color.
Lab Time
• Making Your Own Soil Profile
• Part 1: Illustrating the Soil Profile You are
• Part 2: Creating your Own Edible Soil Profile
Understanding Water Holding Ability
• What is Moisture holding Capacity?
– Moisture holding capacity is the ability of the soil
within the soil profile to retain water.
What is available to the plants?
• Available soil moisture is the water in the
soil that can be used by plants.
– When moisture levels are high, plants can
easily extract moisture from the soil.
– As the water is used, soil moisture tension
• Soil moisture tension is the force by
which soil particles hold on to moisture.
How do we determine how much
moisture the soil can hold?
• Moisture holding capacity is determined primarily
by the soils texture.
– As a rule, the finer the texture of the soil, the more
moisture it will hold.
– A soil high in sand will hold less water.
– Soils high in clay, hold water and keep it from percolating
out of the root zone.
– If the soil is entirely clay, it will hold the water too tightly.
– This means less water is available to plants than if silt
were present.
– A good silt loam holds the most moisture available for
• The amount of moisture the soil can hold for
plants is referred to as available water holding
Available water holding capacity
depends on:
• 1. How deep the soil profile is.
• 2. The type of soil texture found
throughout the soil profile.
– On average, the following textures will hold the
designated amount of moisture per inch of soil:
– fine textured
.20 inches
– moderately fine textured .25 inches
– medium textured
.30 inches
– moderately coarse textured
.20 inches
– coarse textured
.10 inches
How do you know figure the water
holding capacity
• To determine the available water holding
capacity for a given area, multiply the depth of
each horizon, to a maximum depth of 60
inches, by the amount of water the texture
within that horizon can hold.
• Add the totals for each horizon to calculate
total water holding capacity.
• A horizon: 9 inches deep, medium texture = 9
× .30 =2.70 inches
• B horizon: 23 inches deep, moderately fine
texture =
23 × .25 = 5.75 inches
• C horizon: 28 inches deep, medium texture =
28 x .30 = 8.40 inches
• Total = 16.85 inches of water
Water Holding Experiment!
• 1 Jar of Sand, I Jar of Black Soil: Which do you
think will hold more water? Why?
• LAB: We have 3 Different Soils we are going to
test the water holding capacity of:
– Sandy
– Clayey
– Loamy
Understanding Soil Degradation
• Soil degradation is a lowering of the quality of soil or
the loss of soil productivity.
• Soil degradation occurs because people do not
understand soil and the consequences of certain of
its uses.
• Minimizing soil degradation is important in
maintaining a good environment.
• Soil degradation results from:
– Construction
– Contamination
– Erosion
How can construction result in soil
• Construction is altering land by building:
– Roads
– Houses
– Offices
– Factories
– Other structures
• Construction degrades the soil by replacing productive land
with structures that prevent the production of plants or
• Construction degrades the soil when native grasses and
trees are removed.
• This leaves the soil unprotected from erosion.
Construction and Soil Degradation
• Large equipment may move topsoil around and cover it with
• Soil can be compacted when wet by heavy equipment.
• Digging deep into the earth brings up subsoil and parent
• When it is spread on the surface, fertility is lowered.
• Native grasses and trees are removed leaving soil
unprotected from erosion.
• Topsoil is covered with subsoil.
• Soil is compacted and mashed into deep ruts when it is wet.
• Digging deep into the earth brings up parent material and
subsoil that is spread on the surface, lowering the fertility.
What are the sources of contamination
and how do they result in soil
• Contamination results when chemicals, oil, and other
substances leak into the land.
• Some contaminants soak into the soil and destroy its ability
to support plant growth.
• Other materials may pass through the soil and enter the
ground water.
• This can contaminate water supplies.
• Land formerly used as dumps, mines, and factory
sites may be rehabilitated.
• This involves removing contaminated soil and
covering what remains with non contaminated soil.
– This process is expensive.
• Land formerly used as dumps, mines, and
factory sites may be rehabilitated.
• This involves removing contaminated soil and
covering what remains with non contaminated
– This process is expensive.
• Soil may be contaminated by agricultural practices,
such as:
– Use of too much fertilizer.
– Use of excess chemicals.
– Use of irrigation water containing salt
What is soil erosion and how does it
result in soil degradation?
• Soil erosion is the process by which soil is
Natural causes
• Natural erosion shapes the earth’s
landscape by rounding off mountains and
filling in valleys which may form new,
highly fertile areas.
– An example is the Mississippi River Delta.
Soil Erosion Continued
Human actions
• Human activity, such as construction and
plowing may cause accelerated erosion,
which removes topsoil at an excessive
– In many places, soil is being lost faster than
it is being formed.
• This will result in loss of soil fertility and
What are other sources of soil
• Improper irrigation practices
• Growing crops without replacing plant nutrients
• Pollution of soils with chemicals, industrial waste,
human waste and livestock waste
• Overgrazing and deforestation
• Compaction
• Improper irrigation practices result in salinization,
alkalization and water logging.
• Salinization is an accumulation of soluble salts.
• Alkalization is an accumulation of exchangeable
• Both of these are harmful to plant growth
Other Sources of Soil Degradation
• Growing crops without replacing plant nutrients
and soil organic matter.
• These soils are “mined” of nutrients.
• As fertility drops, soil organic matter is lost and
soil structure deteriorates.
• Pollution of soils with chemicals, industrial waste,
human waste and improperly handled livestock
• A large accumulation of heavy metals, salts or an
acute accumulation of chemicals can render soil
• Overgrazing, deforestation and other practices
that remove productive plant cover cause a
condition called desertification.
– This problem is most common in low rainfall areas.
• Humus content and fertility drops.
• Surface soil is exposed and becomes subject to
• Compaction is the packing of soil particles tightly
together after years of tillage with heavy
• It can break down soil structure.
• Plant growth is reduced, organic matter drops,
permeability is lost, and runoff increases.
Doing the Research!