The Origin and Depletion of Soil

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The Origin and Depletion of Soil

• Ben Rudy
• Apr. 7 2003

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Introduction

• Less than 3 percent of the population in the
  United States is employed in production
  agriculture.
• Yet, 2/3 of the population is engaged with
  agri-business.
• In other words, the majority of the population is
  likely to neglect the soil, unless they are
  educated on its importance.

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Soil vs. Dirt

• What is the definition of Soil

The top layer of the earth's surface,
consisting of rock and mineral particles mixed
with organic matter that supports plant growth.
What is the definition of Dirt
Any foul or filthy substance, as excrement, mud,
dust, etc.
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Factors in Soil Formation

• Parent Material

• Climate

• Topography

• Native Vegetation

• Time

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Parent Material

• Definition the material from which soil
  develops.
• The parent material can often be found at the
  soil surface or a few feet below the surface of
  the ground.
• Parent material can consist of Limestone,
  Sandstone, Shale, Peat, etc.

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Parent Material (cont.)

• Not all parent material is formed in place, or
  residual soils.
• Parent material moved by streams are call
  Alluvial deposits.
• P.M moved by lakes are call Lacustrine deposits.
• P.M. moved by the winds are call Loess deposits.
• Colluvial deposits are moved by gravity.
• Glacial deposits are moved by glaciers.

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Parent Material (cont.)

• The parent material and how the material was
  deposited influences the soils fertility and
  texture.

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Climate

• The climate effects the rate at which the parent
  material weathers.
• Climatically factors include
• Temperature
• Precipitation (amount and type)
• Location (Is the area on a slope, ridge or
  valley?)

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Topography

• Slope
• Effects the material being moved and material
  left behind by pulverizing it.
• Exposes subsoil at the upper portion of the
  slope.
• Effects the distribution of water on the Earths
  surface.

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Topography (cont.)

• Drainage or Lack of
• On non-level ground water runs off the surface
  and takes some soil with it.
• On level ground, water soaks in and moves through
  the soil in a process called percolation.
• Soils that are well drained are usually gently
  rolling hills, and are productive for row crops.

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Drainage or Lack of (cont)

• Soils that are poorly drained are less
  productive, because of high water table.
• The soil becomes saturated so that little to no
  air is present. This causes the fungi, bacteria
  and other organisms to slow down or die.

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Native Vegetation

• Animals and micro-organisms mix soils and form
  burrows and pores.
• Plant roots open channels in the soils. 
  Different types of roots have different effects
  on soils. 
• Grass roots are "fibrous" near the soil surface
  and easily decompose, adding organic matter. 
• Taproots open pathways through dense layers.

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Native Vegetation

• Micro-organisms affect chemical exchanges between
  roots and soil.
• Humans can mix the soil so extensively that the
  soil material is again considered parent
  material.

How is it possible that humans can mix the soil
so much it is considered parent material?
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Time

• Soil formation processes are continuous.
• Over time, soils exhibit features that reflect
  the other forming factors.
• Such as recently deposited material from a flood,
  that do not show any signs of soil development

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Soil Texture

• Sand
• Silt
• Clay

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Soil Texture

• The definition of soil texture is the size of
  individual soil particles.
• The larger the soil particle the courser the
  material feels when rubbed between the fingers.
• The largest soil particle is sand, and the
  smallest particle is clay.

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Soil Texture (cont.)

• Soils are rarely composed of pure sand, silt, or
  clay. They are usually composed of a mixture of
  all three components.
• Loam Soil Less than 52 sand, 28 to 50 silt,
  and 7 to 27 clay.

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Soil Texture (cont.)

• Sand
• Largest soil particle
• 2mm to .05mm in diameter
• Extremely poor water holding capability.

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Soil Texture (cont.)

• Silt
• Smaller particle than sand.
• .05mm to .002mm in diameter.
• Help hold water in the soil.

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Soil Texture (cont.)

• Clay
• Smallest soil particle.
• Less than .002mm in diameter.
• Has a negative charge.
• Helps hold water in the soil.
• Important to soil fertility.

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Relative Size of Soil Particles
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Soil Texture (cont.)

• Course-Texture (Sandy) Soil
• Loose and single grained.
• When squeezed in the hand while dry, it will fall
  apart when released.
• When wet, it will form a cast, but will crumble,
  when touched.

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Soil Texture (cont.)

• Medium-Text (Loamy) Soil
• Relatively even mixture of sand, silt, and clay.
• Feels somewhat gritty, but yet smooth.
• When wet, it will form a cast and can be handled
  easily without breaking.

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Soil Texture (cont.)

• Fine-texture (Clay) Soil
• Forms hard clods when dry.
• Very sticky then wet.
• Forms a long flexible ribbon when moist.

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Soil Texture Triangle
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Soil Structure
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Soil Structure

• Soil Structure is the tendency for soil particles
  to cluster together and function as soil units or
  aggregates.
• Aggregates or Peds contain sand, silt, and clay
  and are held together by a gel material formed
  from organic matter.

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Soil Structure (cont.)

• Advantages of a good soil structure
• Peds absorb and hold water better than single
  particles.
• They also hold nutrients and influence chemical
  reactions.
• Resists damage from falling raindrops.

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Soil Structure (cont.)

• Disadvantages
• Dispersed soil particles run together and form a
  crust on the surface of the soil.
• Crust prevents air and water from entering or
  exiting the soil.

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Soil Structure (cont.)

• Granular
• Resembles cookie crumbs and is usually less than
  0.5 cm in diameter.
• Commonly found in surface horizons where roots
  have been growing.

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Soil Structure (cont.)

• Blocky
• Irregular blocks
• Usually 1.5 - 5.0 cm in diameter.

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Soil Structure (cont.)

• Prismatic
• Vertical columns of soil that might be a number
  of cm long.
• Usually found in lower horizons.

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Soil Structure (cont.)

• Platy
• Thin, flat plates of soil that lie horizontally.
  
• Usually found in compacted soil.

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Soil Horizons
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Soil Horizons

• O horizon
• Surface layer.
• Comprised of organic matter and some mineral
  matter.
• May or may not be present in all profiles.

R
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Soil Horizons

• A horizon
• Topsoil
• Dark in color.
• Many not be present or maybe several inches deep.
• Contains organic matter and is high in nutrients.

R
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Soil Horizons

• B horizon
• Subsoil
• Usually lighter in color than the topsoil.
• Influences percolation of a soil.
• Can contain a Hardpan.

R
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Soil Horizons

• C horizon
• Parent Material

R
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Soil Horizons

• R horizon
• Bed Rock

R
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Label the Horizions
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Label the Horizions
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Soil pH
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Soil pH

• Soil pH is the measure of how acidic or basic it
  is.
• pH scale runs from 0 to 14
• Acid 0-6
• Neutral 7
• Basic 8-14

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How do soils become acidic?

• Leaching of nutrients.

• Crop removal of nutrients.

• Acids formed by fertilizers.

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Soil pH (cont.)

• Certain crops may have problems growing in soils
  that are too acidic or basic. Therefore
  producers run soil tests to measure the soils pH
  and nutrient content.

• What would the producer add to his fields if the
  soil was too acidic?

Lime
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Soil pH (cont.)

• Some crops, like blueberries require a acidic
  soil (4.0 to 5.0) a sulfur based material is
  added.
• The pH range for most soils, range from 4.0 to
  10.0.

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pH Scale
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pH scale for Forages
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pH scale for Row Crops
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Soil Ecosystem

• Plant Life,
• Microorganisms,
• Macroorganisms

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Soil Ecosystem

• Ecosystem is all of the plant and animal life
  that live in an area.
• All plants and organisms depend on each other to
  provide food and other environmental factors.

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Soil Ecosystem

• Plant Life
• The soil provides a support for the root system.
• Majority of all nutrients used by the plant are
  found in the soil.
• The area that contains the roots of a plant is
  called the rhizosphere.

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Soil Ecosystem (cont.)

• Microorganisms
• They live in the rhizosphere.
• Many live off plant roots.
• Help decompose dead material.
• Carbon Cycle

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Carbon Cycle
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Common Microorganisms

• Bacteria
• Rhizobia Nitrogen-fixing
• Found on the roots of legumes.
• Converts nitrogen in the air to a plant usable
  form.
• Can be transferred to other fields by
  transplanting the legume.

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Common Microorganisms

• Fungi
• Plant-like organisms that contain no-chlorophyll.
• Size microscopic to large mushrooms.
• Aid in the break down of dead plants.
• Especially the breakdown of lignin, a primary
  component of wood.

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Common Microorganisms

• Nematodes
• One of the MOST important microscopic animals.
• They have smooth round bodies that are not
  segmented and move by fluid pressure.

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Nematodes (cont.)

• Three groups of Nematodes

• Consume decaying organic matter

• Consume other microorganisms

• Consume plant parasites

MOST IMPORTANT!!
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Nematode
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Macroorganisms

• Earthworms
• Enhance the soil by
• Burrowing
• Pulling Organic matter from the surface down into
  the soil.
• Castings

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Macroorganisms

• Grub worms
• Feed on plant roots, and can become Very
  Destructive!

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Macroorganisms

• Groundhogs, moles, chipmunks, and other burrowing
  animals
• They create large passages that allow air and
  water to enter the soil.
• Help incorporate organic material into the soil.
• Very Destructive to plants.
• Holes and burrows can be hazardous when operating
  equipment.

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Erosion
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Erosion

• Define Erosion.

The wearing or washing away of the soil.
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Main Kinds of Erosion

• Wind Erosion

• Water Erosion

• Splash Erosion

• Sheet Erosion

• Rill Erosion

• Gully Erosion

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Wind Erosion

• What is it?

• Wind erosion is the movement and deposition of
  soil particles by wind.

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What causes wind erosion?

• A sparse or absent vegetative cover
• A loose, dry and smooth soil surface
• Large fields
• Strong winds

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Wind Erosion Model
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Are their any soils resistant to wind erosion?

• Loams, clay loams and silt loams are generally
  more resistant to wind erosion.

• Soils with more organic matter are more resistant
  to wind erosion.

What type of soils are least resistant to wind
erosion?
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Ways of Decreasing Wind Erosion.

• No-till
• Avoid burning fields
• Do not overgraze pastures

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Water Erosion

• Mechanism of water erosion

• Detachment
• Example Raindrop hitting the soil surface.

• Transportation

• Deposition

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Splash Erosion

• Impact of rain drops soil granules.

• Detaches and transports soil.
• Up to 2 feet by air.
• 3-5 feet by water.

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Splash Erosion
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Sheet Erosion

• Soil is removed uniformly from every portion of
  the slope.
• This type of water erosion in not very
  noticeable.
• But can be recognized by soil deposition at the
  bottom of a slope.

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Rill Erosion

• The most common forms of erosion.
• The removal of soil by concentrated water running
  through little streamlets.
• The rill channels can temporarily be removed by
  tillage.

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Gully Erosion

• Severe soil erosion.
• Large rills that cannot be crossed with
  equipment.
• Carry large amounts of water after rains.

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