Download Soil Characteristics

Soil Formation
Soil Physical Properties
• Slope is defined as the angle of
the soil surface from horizontal.
• It is expressed as the % of rise
over run.
Soil Physical Properties
• Slope effects the productive
potential in numerous ways:
Rain runoff, soil erosion, the
use of farm machinery, and
contour farming.
Soil Physical Properties
• Texture refers to the proportions of
sand silt and clay in the soil.
• Course-textured soils are and
sandy and do not hold water well,
while fine-textured soils contain
clay and tend to hold more surface
moisture.
Soil Physical Properties
• Flood hazard refers to the
likelihood that the soil will
flood.
• This may occur in flood plains
near rivers and greatly reduce
plant production.
Soil Physical Properties
• Erosion as a soil property,
refers to the degree that the soil
has already been damaged.
• May range from none to severe.
Soil Physical Properties
• A field used for crop production
that has little or no erosion can
continue to be used for crops.
• But a severely eroded field may
need to be turned into pasture
where it is always covered.
Soil Texture
• Soil Texture
• What is Soil Texture?
– It is the proportion of three sizes of soil
particles.
• Which are:
– Sand (Large)
– Silt (Medium)
– Clay (Small)
Soil Texture
Effects of Particle Size?
Soil particle size affects two important soil features:
They are internal surface area
The numbers and size of the pore spaces
Soil Texture
What is the internal surface area ?
It is the area of soil that the total surface are of the particles in
the soil.
So the smaller the soil particles the greater the internal surface
area will be.
Soil Texture
Pore size and number:
this depends on the particle size.
So there are more pores that are found between the larger
particles.
Soil Texture
What is a Soil Separates?
They are categories that scientist have divided up
into three groups
The three groups are:
Sand
Silt
Clay
Soil Texture
What is Sand?
It is the largest and is further divided into
four subcategories.
They are:
Very coarse sand
Coarse sand
Medium sand
Fine Sand
Soil Texture
Sand
it is the larges soil separate and is composed mainly of
weathered grains of quartz.
Sand is also gritty to the touch.
Sand grains will not stick to each other.
Soil Texture
Sand
What will sand do to the soil?
It will improve the soil by
improving the water infiltration
and aeration
Soil Texture
Silt
is the medium sized soil separated.
Silt particles are silky or powdery to the touch
Silt grains will not stick to one another just like sand grains.
Silt is the best soil as it has the ability to hold large amounts
of water in a form plants can use.
Soil Texture
• Clay
– is the smallest size soil separate.
– It is composed of tiny crystals
– Clay is formed by chemical reactions between
weathered minerals to form tiny particle of new
minerals.
– Clay will hold more plant nutrients than any
other separate.
– Clay grains will stick to one another.
Soil Texture
Pass out picture of triangle
and lets see if we can classify
some soils.
Soil Texture Triangle
Soil Texture
1.
40% sand 22% clay and 38%
silt
What is the soil classified as?
Soil Texture
2.
90% sand 10 % clay and 25 %
silt
What is it?
Soil Texture
Lets go and texture some of the samples that we have.
See if you can make a ribbon and with which one?
Which one feels grittiest?
Which one feel powdery?
Soil Structure
What are the three grades of structured soils?
A. Weak structure: peds are hard to distinguish.
Only a few can be separated from the soil.
B. Moderate structure: peds are visible and can be
handled without breaking up.
C. Strong structure: most of the soil is formed into
peds.
Soil Structure
The six principle soil structural classes:
A. Granular
B. Prismatic
C. Massive
D. Blocky
E. Platy
F. Single grain
Soil Structure
• Soil structure: Soil particles cling together
by various reasons such as moisture,
earthworms, and the movements of plant
roots. Groups of clinging particles are
called peds or soil aggregates.
Soil Drainage
• Permeability
– Soil permeability is the property of the soil pore system
that allows fluid to flow. It is generally the pore sizes and
their connectivity that determines whether a soil has high
or low permeability. Water will flow easily through soil
with large pores with good connectivity between them.
Small pores with the same degree of connectivity would
have lower permeability, because water would flow
through the soil more slowly. It is possible to have zero
permeability (no flow) in a high porosity soil if the pores
are isolated (not connected). It is also to have zero
permeability if the pores are very small, such as in clay.
Soil Drainage
• Porosity
–Porosity of a soil is the volume of
all the open spaces (pores) between
the solid grains of soil. For growing
things in soil, the porosity is
important as it defines the volume of
water that can be held in a given
volume of the soil.
Characterizing Soils
• The Soil Profile
• Most soils have three distinct
layers called horizons.
• The horizons are called A
Horizon (topsoil), B horizon
(subsoil), and C horizon (parent
Characterizing Soils
• The top soil is the most
productive because that is
where all the nutrients are.
The Soil Profile
• What is a horizon?
–They are the layers of the
different types of soil and the
different depths that the layers
will be located at.
The Soil Profile
• What is a soil profile?
–It is the vertical section
through the soil and
extending into the
unwreathered parent materials
and exposing all the horizons.
Master Horizons
• What is the Master Horizons?
– The are A, B and C horizons are
known as the master horizons. They
are a part of a system for naming
soil horizons in which each layer is
identified by a code O, A, E, B, C
and R
Horizons
The O HorizonIs the organic layer made of wholly
or partially decayed plant material
and animal debris . You can
normally find this layer in a forest
with fallen leaves, branches and
other debris.
Horizons
• The A Horizon– It is usually called the topsoil by most farmers.
This is where the organic matter accumulates
over time. This layer is very prone to leaching
and losing iron and other minerals. The A
horizon provides the best environment for the
growth of plant roots, microorganisms and
other life.
Horizons
• The B Horizon– This is also called the subsoil is often called the
zone of accumulation where chemicals leached
out of the A horizon
Horizons
The C Horizonlacks the properties of the A and
B horizon. It is the soil layer
that is less touched by soil
forming processes and is
usually the parent material soil
Parent Material
• Soil parent materials are those
materials underlying the soil and
from which the soil was formed.
• There are five major categories of
parent material: minerals and
rocks, glacial deposits, loess
deposits, alluvial and marine
deposits and organic deposits.
Parent Material
• Minerals are solid, inorganic,
chemically uniform substance
occurring naturally in the earth.
• Some common minerals for soil
formation are feldspar, micas,
silica, iron oxides, and calcium
carbonates.
Parent Material
• Rocks are different from
minerals because they are not
uniform.
• There are three types of rocks,
igneous, sedimentary, and
metamorphic.
Parent Material
• Igneous rocks are those formed
by the cooling of molten rock.
• Sedimentary rocks are those
formed by the solidification of
sediment.
Parent Material
• Metamorphic rocks are simply
igneous or sedimentary rocks
which have been reformed
because of great heat or
pressure.
Parent Material
• During the ice age, glaciers moved
across areas of the northern
hemisphere.
• They ground, pushed, piled,
gouged, and eventually deposited
great amounts of rocks, parent
material, and already formed soil
material.
Parent Material
• Loess deposits are generally
thought of as windblown silt.
• Alluvial and marine deposits are
water borne sediments.
• Alluvial deposits are left by
moving fresh water.
• Marine deposits are formed on
ancient ocean floors.
Parent Material
• Organic deposits are partially
decayed plants that live plants
are able to root and grow in.
• These are found in swamps and
marshes.
Weathering
• When minerals are exposed to
weather, they begin to break
down into smaller pieces.
• This is mostly done by heating
and cooling of the minerals and
rock.
Weathering
• Some minerals are water
soluble which means they
dissolve when exposed to water.
• Some rocks may contain some
minerals that are water soluble
and only that part of the rock
will dissolve. Ex: some caves.
Weathering
• When a tree or other types of
plants begin growing in the
cracks of rocks, this may speed
up the break down of the rock
because of the pressure the
roots may exert.
Weathering
• Ice can also speed up the
weathering process on rocks.
• If a rock has a crack that can fill
up with water, when the water
freezes, it can literally crumble
the rock into small pieces.
Weathering
• Rocks can also be broken down
by mechanical grinding such as
wind blowing sand at high
speeds or glaciers causing rocks
to grind each other.
Weathering
• New soil is continually being
made, but it takes a long time to
create new soil and if it isn’t
managed properly, soil can be
eroded away quicker than it can
be made.
Soil
• a layer of natural materials on
the earth’s surface containing
both organic and inorganic
materials and capable of
supporting plant life.
Soil
• The material covers the earth’s
surface in a thin layer.
• It may be covered by water, or
it may be exposed to the
atmosphere.
Soil
• Soil contains four main
components: inorganic material,
organic matter, water, and air.
Soil
• Ideal soil should contain about
50% solid material and 50%
pore space.
• About half of the pore space
should contain water and half of
the space should contain air.
Soil
• Inorganic material consists of
rock slowly broken down into
small particles.
• The organic material is made up
of dead plants and animals
varying in stages of decay.
Soil
• The percentages of the four
main soil components varies
depending on the kind of
vegetation, amount of
mechanical compaction, and the
amount of soil water present.
Soil
• Soil is formed very slowly.
• It results from natural forces
acting on the mineral and rock
portions of the earth’s surface.
• The rock is slowly broken down
to small particles resulting in
Organic Matter
• In most soils, the proportion of
organic matter is relatively
small (2-5%).
• Its importance in formation and
production is much higher than
the small % would suggest.
Organic Matter
• Soil organic matter decaying
plant and animals.
• As they die, they are attacked
by microorganisms: fungi,
bacteria, and others.
Organic Matter
• There are two types of organic
matter.
• Original tissue is that portion of
the organic matter that can still
be recognized.
• Twigs and leaves covering a
Organic Matter
• Humus is organic matter that is
decomposed to the point where
it is unrecognizable.
• The brown color you sometimes
see in soil is a good example.
Organic Matter
• Purposes of organic matter: affects
the soil structure by serving as a
cementing agent, returns plant
nutrients to soil (P, S, N), helps
store soil moisture, makes soil
more tillable for farming, provides
food (energy) for soil
microorganisms, which makes the
Additional Resources
• http://soils.usda.gov/education/
• Water Movement in Soil Video (Click Below)