Soil is described in terms of physical and biological components' Both of these components are impor

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Soil - Unit Overview

• Soil is described in terms of physical and
  biological components. Both of these components
  are important in establishing a foundation of
  soil knowledge, essential for good, sustainable
  management.

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Soil Components
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Organic Matter

• Living about 15 - living leaf
• Recently dead - produce nutrients,
• - dead leaf
• Long dead stable, holds nutrients, humus-
  decomposed leaf

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Air and Water

• Occupy the same pore space
• Essential for soil life

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Soil Particles

• Sand largest O 20-40x
• Silt medium o 25x
• Clay smallest . 1
• Pore space varies with size of particles

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Soil Texture
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Characteristics of the Various Soil Classes
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Soil Horizon
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Soil Structure Categories
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Factors which affect soil structure

• Organic Matter Content
• Soil Organisms
• Soil Colloids
• Tillage
• Freezing and Thawing
• Water Movement

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Organic Matter Content

• May be increased by
• Adding manure
• Growing cover crops
• May be decreased by
• Tillage
• Hot,
• Humid
• environment

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Soil Organisms

• Bacteria in soil have sticky
• substance on cell wall.
• This glue holds soil particles
• to bacteria and to each other.
• This binds soil particles into larger particles.
• Fungi produce thread-like structures called
  mycelia which bind soil particles and peds
  making larger particles.

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Soil Colloids

• Very small particles with a weak electric charge.
  o o-
• The charge causes water to bind to particles.
• As water evaporates, colloids and larger
  particles draw together, creating even larger
  particles.

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Tillage

• Positive effect
• Creates air space in soil, allowing organisms
  needed oxygen
• Negative effect
• Disrupts the soil structure and kills the larger
  organisms such as earthworms.
• If done when too wet or dry, may destroy the soil
  structure of the tillage zone.

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Freezing and Thawing

• As water in soil freezes it expands, pushing soil
  particles apart.
• This opens pore spaces for air.
• As water thaws, pore spaces tend to remain
  temporarily.
• This can be enough to encourage soil organisms,
  by allowing more oxygen.

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Water Movement

• Positive
• As water moves vertically through the soil some
  of the water is stored, and can be used by crops.
• Negative -
• Vertical movement of water can cause leaching of
  minerals.
• Vertical movement in soil freshly tilled may
  cause collapse and less pore space.
• Vertical movement in clay can result in a hard
  pan.
• Horizontal movement may cause erosion.

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pH

• pH is the measure of the concentration of
  hydrogen ions.
• It is measure on a logarithmic scale going from
  1-14 with 1 being the most acidic (most hydrogen
  ions) and 14 the most basic (least hydrogen
  ions).
• pH of soil is important because certain chemical
  reactions only occur in certain range.
• Not as important for organic systems, because
  they depend on biological reactions more than
  chemical reactions.

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Soil Ecosystem

• Biological model of soil management as opposed to
  the chemical model is the major key to good soil
  management.
• More individual life forms in soil than live on
  the surface of the earth.
• 4 billion bacteria, 1 million fungi per teaspoon
  of soil
• Perform many functions to support plant life

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Biodiversity

• Soil fertility is related to having a large
  number of different types of life forms.
• Different crops depend on different ecosystems.
• Annual field crops bacteria dominated
• Woody perennials fungi dominated

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Producers-herbivores-predators-higher
predators-decomposers
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How the soil food web benefits plant life

• Builds soil structure
• Disease suppression
• Improves nitrogen retention
• Mineralizes nutrients
• Produces plant growth hormones
• Improves crop quality

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Builds soil structure

• Pore space from burrowing.
• Sticky substance from bacteria holds particles
  together.
• Fungal hyphae holds soil conglomerates together

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Disease Suppression

• Population density good organisms take up all
  the niches in the soil so there is no room for
  disease organisms.
• Antibiotics some fungi produce antibiotics
  which destroy certain bacteria.

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Improves nitrogen and other nutrient retention

• Waste given off by organisms contain nutrients.
• Soil organisms retain nutrients in their bodies.
• When organisms die the nutrients are released.

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Mineralizes nutrients

• Organisms can take nutrients that plants cant
  use and change them into a form that plants can
  use, such as nitrogen.
• Chelation Some nutrients are in a form that is
  not available to plants. Soil organisms can add
  an organic molecule, changing their form and
  making them available to the plant.

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Decomposition of plant toxins

• Natural plant toxins, such as phenols and tannin,
  can be detoxified when there is a diversity of
  soil organisms.
• Man-made toxins can also be detoxified by a
  diversity of soil organisms.

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Produces plant growth hormones

• Some plant hormones, such as auxin, can be
  produced by some soil organisms.
• Auxin promotes root growth.

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Improves crop quality

• Not well studied
• Relation between soil biodiversity and nutrient
  quality of food grown in soil
• More proteins, vitamins, anti-oxidants present
  when soil had a diversity of organisms present

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Importance of Carbon

• Basis for all life
• Cells 70-95 water the rest carbon compounds
• All organic compounds are carbon compounds

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Carbon Cycle
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Importance of nitrogen

• Nitrogen is part of proteins and nucleic acids so
  is needed by every living organism
• Free nitrogen (nitrogen gas) makes up about 78
  of the atmosphere but is not available to plants
• Plants must absorb nitrogen compounds from the
  soil

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Nitrogen Cycle
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Summary

• Soil properties
• Composition of soil
• Texture sand, silt, clay, loam
• Structure pore space
• Soil biology, ecosystems
• Soil life produces nutrients, builds structure
• Trophic levels
• Soil nutrient cycles
• Carbon cycles through organic matter and carbon
  dioxide
• Nitrogen cycles through nitrogen gas and nitrogen
  compounds to proteins and nucleic acids