Soils

1
Soils Growing Media
2
What is Soil?

• A naturally weathered part of the earths surface
• A fundamentally important part of plant growth
  (in most cases), but not absolutely crucial (not
  essential)

3
What are Soil Functions? (as related to plant
growth)

• Source of mineral nutrients
• Source of water (H2O)
• Anchorage

4
Soil Properties of Horticultural Interest

• Physical
• Room for air and water to move in soil
• Room for root growth
• Structural base for plant anchorage
• Chemical
• Plant nutrient source and reservoir

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5 Soil Components - Ideal Soil
Space portion
Solid portion
1
Inorganic minerals 45-47
3
Air 25
2
Water 25
4
Organic matter 3-5
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Inorganic Mineral Component

• Most of solid part of soil - 45/-
• Important in plant anchorage
• Soil particles are classified by size
• Sand - largest - coarse
• Silt - intermediate
• Clay - smallest - fine

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Inorganic Mineral Component

• Provides some minerals that are plant nutrients
• Depends on the rock from which the soil was
  formed (parent material)
• A portion of these minerals will be dissolved in
  the soil water
• Provides a place for other nutrients to attach so
  they stay in the soil and are held there for
  plant roots to access

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Holding Other Nutrients

• Nutrients are held because
• Soil particles are electrically charged
  (generally negative. - - -)
• Nutrient particles (ions) are electrically
  charged (generally positive, )
• This characterisitic of soil is called

Cation Exchange Capacity
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Cation Exchange Capacity
Fe
Fe
K
K
K
Fe
K
K
K
Fe
K
Fe
Fe
Fe
K
K
K
Fe
Fe
10
Cation Exchange Capacity

• Mostly on small, clay particles
• Prevents nutrient loss (leaching)
• Soils vary in their CEC (Cation Exchange
  Capacity)
• Nutrients are exchanged by roots (removed from
  soil particles and moved into xylem of root)

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What minerals are plant nutrients, anyway?

• Major Nutrients and their Roles
• Nitrogen N proteins/DNA
• Phophorus P energy storage/DNA
• Potassium K metabolism
• Calcium Ca cell walls
• Sulfur S proteins
• Magnesium Mg chlorophyll

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Minor minerals (less needed)

• Iron
• Zinc
• Manganese
• Copper
• Boron
• Molybdenum
• Chlorine
• (Cobalt, Nickel)

13
What influences nutrient uptake by a plant from
soil?

• How much nutrient is in the soil
• Solubility of the nutrient ion (Fe, K, etc.)
• CEC of the soil
• Soil pH (acidity vs. alkalinity)
• How much organic matter is in soil

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Horticulturally, which can we
influence?

• How much nutrient is in the soil
• How? - add fertilizer
• Solubility of the nutrient ion (Fe, K, etc.)
• CEC of the soil
• Soil pH (acidity vs. alkalinity)
• How? - add lime (Ca Mg) or sulfur
• How much organic matter is in soil
• How? - add O. M.

15
Space Component
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Space Soil Water

• Water occupies spaces between soil particles
• Large spaces drain fastest, small spaces hold
  water longer

17
Space Soil Air (Atmosphere)

• Air occupies spaces between soil particles
• 100 relative humidity
• Very different in composition from air above
  ground
• Elevated carbon dioxide - CO2
• Reduced oxygen - O2

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Space Air Water

• Both occupy the same space
• Thus, when space is filled with one (ie. water)
  it is not filled with air
• Both are, of course, essential
• Need balance of air and water
• Remember Large spaces drain fastest (air), small
  spaces hold water longer (water) so a mix of size
  spaces is best!

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Organic Matter Component

• O.M. is small part of soil by volume (3-5)
• Composed of once-living matter
• Plant/animal material debris

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Functions of O.M.

• Water holding
• Nutrient holding (contributes to CEC of a soil)
• Nutrient source via decomposition
• Soil structure (helps clump soil particles
  together making spaces for air and water larger)

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O. M. as Nutrient Source

• Decomposition results in
• Carbohydrates CO2
• Proteins/DNA,RNA N
• Other nutrients
• (P, K, Mg, Ca, etc.)

decompose to
Available To plants
decompose to
22
O. M. Changes Soil Structure

• O. M. and organic acids it produces glue the
  mineral soil particles together
• Increases the size of spaces between particles

23
Mineral Soil without O.M.
All small spaces between particles
24
Mineral Soil with O.M.
Large spaces between clumps
Small spaces within clumps
Organic Matter Glue
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Horticulturally speaking, what can be done about
O.M.?

• In the field - grow cover or green manure crops
  and plow into soil
• In greenhouse - mix O. M. with other materials
  (ie. sphagnum peat moss)
• In garden - compost or sphagnum, etc.

26
Soil Organisms Component

• Micro- and macro-organisms
• Algae, bacteria, fungi, nematodes
• Earthworms, insects, moles, etc.
• Some are beneficial, some are harmful
• Serve many functions

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Functions of Organisms

• Decompose Organic Matter
• Open spaces between soil particles (tunneling,
  burrowing, etc.)
• Change (fix) nitrogen from air to a form plants
  can use
• Form symbiotic (mutually beneficial)
  relationships with plant roots for water and
  nutrient uptake - mycorrhizae

28
Functions of Organisms

• Compete with plants for water, nutrients, air
• Infect plant tissues and cause disease

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Horticulturally, what?

• Eliminate harmful micro-organisms by
• Pasteurization (heating, steaming) of greenhouse
  media
• Chemical applications to the field
• Add beneficial micro-organisms
• Rhizobium (N fixation)
• Mycorrhizal fungi

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Summary

• Soil is complex
• Physical, chemical, and biological properties of
  importance

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Summary (contd.)

• A soil (growing medium) should provide
  nutrients, water, air
• Five components

Space portion
Solid portion
Inorganic minerals 45-47
Also, Soil micro- organisms they occur in the
space portion of soil
Air 25
Water 25
Organic matter 3-5
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Container Growing Media
When is soil not really soil?
Answer When it is a growing medium!
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Container Horticulture

• Greenhouse
• Landscape planters
• Houseplants
• Interiorscapes

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Characteristics of Medium

• Adequate CEC
• Aeration/drainage
• Water holding capacity
• Free of disease/pests/toxins
• Lightweight
• Inexpensive
• Uniform and reproducible
• Readily available

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Soil or No Soil?

• A root-zone medium may contain some soil with
  other components (soil-based), or it may contain
  no soil at all (soilless)!
• If there is any soil in the medium, in order to
  be effective, the soil component of a soil-based
  mix must be at least 20 of the total volume of
  medium.

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Medium Components

• Soil - Sands to clays
• Highly variable in all characteristics
• Problem is reliable continuing source
• Sand - large size soil particles
• Large pore spaces means aeration/drainage
• Cheap, but heavy (too weighty to ship very far)

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Medium Components

• Perlite - lava heated to 1400F
• High water holding
• No CEC
• Promotes aeration
• Sterile and lightweight
• Vermiculite - mica heated to 2000F
• High water holding
• High CEC
• Sterile and lightweight

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Medium Components

• Peat - part decomposed residue of wetland sedges,
  sphagnum moss, etc.
• High water holding
• High CEC
• Promotes aeration
• Coir - coconut husk fibers
• Some of same characterisitics as sphagnum

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Medium Components

• Wood chips, sawdust, bark chips
• Must be composted to remove toxins
  (ie. ammonia)
• Cheap
• May rapidly decompose consuming N
• Other locally available materials
• Cottonseed hulls, rice hulls, etc.
• Variable characteristics