Soil and Plant Growth

1
Soil and Plant Growth

• What is soil?
• As a medium for plant growth, soil can be
  described as a complex natural material derived
  from disintegrated and decomposed rocks, and
  organic materials, which provides nutrients,
  moisture,and anchorage for land plants

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Four principal components of soil

• 1. 45 Minerals (clay, sand, or silt particles)
• 2. 25 Air
• 3. 25 Water
• 4. 5 Organic matter (living dead)

3
How soils are formed?

• This is a long term process that involves both
  physical chemical weathering, along with
  biological activity.
• It can take 100 years to form 1 of topsoil

4
Characteristics involved in forming soil.

• Parent Material material from which soils are
  formed.
• Climate Temperature and moisture.
• Living Organisms microscopic macroscopic
  plants and animals.
• Topography shape position of the land
  surface.
• Time period during which parent material has
  been subjected to soil formation.

5
Plants and Soil

• Nutrients are released by decomposers
• Productive soil is a dynamic process
• Nutrient cycling is key to understanding

6
Soil profile

• Organized into horizons
• O-Organic ( A-Topsoil)
• A-Topsoil
• B-Subsoil
• C-Parent material

7
Soil Texture

• Clay is the smallest
• Silt
• Sand the largest
• Loam a mixture

8
Spheroidal

• Granular Crumb
• (organic matter content is high)

9
Prism-Like

• Prismatic Columnar
• (found in subsoils and common in arid semiarid
  regions)

10
Plate-Like

• Platy
• (can occur in any part of the profile)

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Block-Like

• Blocky
• (most common in subsoils, particularly those in
  humid regions)

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others

• Massive single grain

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Soil structures influence?

• Soil moisture relationship
• Aeration
• Heat transfer
• Root growth

14
Soil Reaction (pH)

• Soil reaction (acidic, neutral, alkaline) refers
  to the relative concentration of hydrogen ions
  (H) and hydroxyl ions (OH-) in the soil

15
Soil Plants

• Nutrient-Holding Capacity
• Water Holding Capacity (permeability)
• Aeration ( porosity)
• pH

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pH

• The acidity or alkalinity of the soil
• pH is not a fixed characteristic of the soil and,
  depending on a number of conditions, varies over
  time.
• Soils in climates with high rainfall humidity
  generally tend to be acid. (This is due to the
  leaching of base elements as well as by harvested
  crops usage of sodium, potassium, calcium,
  magnesium)
• Soils in arid climates tend to be alkaline.

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pH Range

• 0 - 4.0 extremely acid
• 4.1 5.0 strongly acid
• 5.1 6.0 moderately acid
• 6.1 6.9 slightly acid
• 7.0 neutral
• 7.1 8.0 slightly alkaline
• 8.1 9.0 moderately alkaline
• 9.1 10 .0 strongly alkaline
• 10.1 14 extremely alkaline

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pH Range

• The pH for most agriculture soils lies between 5
  and 8.5

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Changing the pH levelof an acid soil

• 1. The pH of an acid soil can be increased by
  adding amendments or fertilizers containing such
  elements as
• Calcium
• Potassium
• Sodium
• Magnesium

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Changing the pH levelof an acid soil

• Calcium Carbonate (CaCO3)
• Also known as agricultural lime
• This is finely ground limestone
• This is effective due to its ability to provide
  calcium (Ca) and hyfroxyl (OH-) ions

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Changing the pH levelof an acid soil

• The prolonged use of chemical fertilizers that
  are residually acid tend to make the soil acid.
  Examples are
• Ammonium Sulfate (NH4)2SO4
• Ammonium Nitrate (NH4NO3)
• Ferrous Sulfate (FeSO4)

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Changing the pH levelof an alkaline soil

• Acid-forming chemicals such as
• Ferrous Sulfate (FeSO4)
• Calcium Sulfate (CaSO4) in some irrigation areas,
  a saturated solution of calcium sulfate is
  allowed to drip into the irrigation water or
  spread as a powder.
• Elemental Sulfar (S) through the process of
  oxidation produces sulfuric acid (H2SO4) and
  acidify the soil

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Changing the pH levelof an alkaline soil

• The prolonged use of chemical fertilizers that
  are residually alkaline tend to make the soil
  more alkaline. Examples are
• Sodium Nitrate (NaNO3)
• Potassium Nitrate (KNO3)
• Calcium Nitrate Ca(NO3)2
• Calcium Carbonate (CaCO3)

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pH and Plant Nutrients

• The availability of certain plant nutrients is
  regulated by the acidity or alkalinity of the
  soil. Examples
• Iron and Zinc become less available to plants as
  the pH increases
• Phosphorus is more available at a soil pH of 6.5
  7 than at either higher or lower values.

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pH and Plant Nutrients

• Calcium availability decreases with increased
  acidity.

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Cation Exchange Capacity

• CEC is an important measure of the fertility and
  potential productivity of a soil
• Clay and organic matter have a net negative
  charge which attract the positively charged
  cations. (se figure 1-9)
• Ca, Mg K NH4 are plant nutrients
• Na H effect soil chemical physical
  characteristics

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Soil Organic Matter

• Helps strengthen soil aggregates
• Improves aeration and water infiltration
• Increases water-holding capacity
• Provides significant amounts of CEC
• Provides buffering against rapid change in soil
  reaction acid 0r alkaline forming materials are
  added to soil

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• Form stable organic compounds that can increase
  the availability of micronutrients.
• Provides a source of many plant nutrients.
• Provides a food source for soil microorganisms.

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Types of organic matter

• Green manure crops
• Crop residues
• Animal manures
• Compost
• Look at Table 1-3

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Soil Organisms
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Soil Organisms

• Micro flora
• Bacteria
• Fungi
• Algae
• You tell me what they do?

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Soil Management

• 1. Tillage (Primary Secondary)
• 2. No-Till or Minimal till
• 3. Conservation (National Resources Conservation
  Service NRCS 2 billion tons of topsoil lost per
  year)
• Best Management Practices (BMP, crop, fertilizer,
  pesticide, water management)