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Soil Formation

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Title: Soil Characteristics Last modified by: Joe W. Kotrlik Created Date: 11/3/1999 4:20:44 PM Document presentation format: On-screen Show (4:3) Company – PowerPoint PPT presentation

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Title: Soil Formation


1
Soil Formation
2
Soil Physical Properties
  • Slope is defined as the angle of the soil surface
    from horizontal.
  • It is expressed as the of rise over run.

3
Soil Physical Properties
  • Slope effects the productive potential in
    numerous ways Rain runoff, soil erosion, the
    use of farm machinery, and contour farming.

4
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.

5
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.

6
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.

7
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.

8
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)

9
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

10
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.
11
Soil Texture
Pore size and number this depends on the
particle size. So there are more pores that are
found between the larger particles.
12
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
13
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
14
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.

15
Soil Texture
Sand What will sand do to the soil? It will
improve the soil by improving the water
infiltration and aeration
16
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.
17
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.

18
Soil Texture
  • Pass out picture of triangle and lets see if we
    can classify some soils.

19
Soil Texture Triangle
20
Soil Texture
1. 40 sand 22 clay and 38 silt What is the
soil classified as?
21
Soil Texture
2. 90 sand 10 clay and 25 silt What is it?
22
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?
23
Soil Structure
  • What are the three grades of structured soils?
  • Weak structure peds are hard to distinguish.
    Only a few can be separated from the soil.
  • Moderate structure peds are visible and can be
    handled without breaking up.
  • Strong structure most of the soil is formed into
    peds.

24
Soil Structure
  • The six principle soil structural classes
  • Granular
  • Prismatic
  • Massive
  • Blocky
  • Platy
  • Single grain

25
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.

26
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.


27
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.

28
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
    material).

29
Characterizing Soils
  • The top soil is the most productive because that
    is where all the nutrients are.

30
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31
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.

32
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.

33
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

34
Horizons
The O Horizon- Is 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.
35
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.

36
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

37
Horizons
The C Horizon- lacks 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
38
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.

39
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.

40
Parent Material
  • Rocks are different from minerals because they
    are not uniform.
  • There are three types of rocks, igneous,
    sedimentary, and metamorphic.

41
Parent Material
  • Igneous rocks are those formed by the cooling of
    molten rock.
  • Sedimentary rocks are those formed by the
    solidification of sediment.

42
Parent Material
  • Metamorphic rocks are simply igneous or
    sedimentary rocks which have been reformed
    because of great heat or pressure.

43
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.

44
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.

45
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.

46
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.

47
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.

48
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.

49
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.

50
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.

51
Weathering
  • New soil is continually being made, but it takes
    a long time to create new soil and if it isnt
    managed properly, soil can be eroded away quicker
    than it can be made.

52
Soil
  • a layer of natural materials on the earths
    surface containing both organic and inorganic
    materials and capable of supporting plant life.

53
Soil
  • The material covers the earths surface in a thin
    layer.
  • It may be covered by water, or it may be exposed
    to the atmosphere.

54
Soil
  • Soil contains four main components inorganic
    material, organic matter, water, and air.

55
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.

56
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.

57
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.

58
Soil
  • Soil is formed very slowly.
  • It results from natural forces acting on the
    mineral and rock portions of the earths surface.
  • The rock is slowly broken down to small particles
    resulting in soil.

59
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.

60
Organic Matter
  • Soil organic matter decaying plant and animals.
  • As they die, they are attacked by microorganisms
    fungi, bacteria, and others.

61
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 forest floor are good
    examples.

62
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.

63
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 soil capable of
    plant production

64
Additional Resources
  • http//soils.usda.gov/education/
  • Water Movement in Soil Video (Click Below)
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