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Science Dept.

Geology and Soils GEO 100 Notes
Soil Physical Properties

  1. Soil Physical Properties

    1. Soil Texture
    2. Soil Structure
    3. Soil Consistence
    4. Soil Color
    5. Soil Temperature
    6. Soil Permeability

  2. Soil Texture - The Smaller the Particle, the More Surface Area Per Gram

    1. Soil Separates

      1. very coarse sand ... 2.0 - 1.0 mm; sand is usually of quartz and micas.
      2. coarse sand .......... 1.0 - 0.5 mm
      3. medium sand ........ 0.5 - 0.25 mm
      4. fine sand ............. 0.25 - 0.10 mm
      5. very fine sand ...... 0.10 - 0.05 mm
      6. silt ...................... 0.05 - 0.002 mm; composed of quartz, feldspar and micas
      7. clay ................ less than 0.002 mm; composed of clay minerals

  3. Soil Textural Classes

    1. Broad Classification

      1. Sands: Greater Than 70% Sand
      2. Silts: Greater Than 80% Silt
      3. Clays: Greater Than 40% Clay
      4. Loams: Mix of Sand, Silt and Clay

    2. Soil Textural Triangle

    3. Mechanical or Particle Analysis: By the Use of Sand Sieves and a Hydrometer for Silt and Clay

    4. Analysis By Feel

    5. Soil Texture And Uses

      1. Sandy

        1. Agriculture: Can Not Hold Water or Nutrients
        2. Erosion: Not Susceptible to Water, Susceptible to Wind
        3. Construction: Spread Footings, Poor Road Bed
        4. On-Site Sewage: Good Perc. Rate, Not Enough Leaching, Bad for G.W.

      2. Clays

        1. Agriculture: Hold Water and Nutrients Tightly - Cloddy, Crusty
        2. Erosion: Can Erode Easily
        3. Construction: Expanding Clays, Compaction Cab Be a Problem
        4. On-Site Sewage: Poor Perc. Rates

      3. Silty

        1. Agriculture: Good
        2. Construction: Shift, Does Not Pack Well

  4. Soil Structure

    1. Type

      1. Platy: Reduced penetration of Roots, Air, and Water - Common in A2
      2. Prisimlike

        1. Prismatic: Flat or Pointed Tops
        2. Columnar: Rounded Tops
        3. Found in B (montmorillonite clay) of MidWest and Na Soils of the Great Plains

      3. Blocky:

        1. Angular ~ 90o in B2
        2. Subangular Less Than 90o in B1 and in B3

      4. Granular or Spheroidal: If Porous = Crumb - Common in A1 and in Ap
      5. Structureless

    2. Structural Class: Various Sizes of Structural Units

    3. Distinctness: Degree of Development

  5. Formation of Soil Structure

    1. Soil Structure

      1. Ca, Mg, and H: Good Soil Structure
      2. Na: Soil Structure Destroyed

    2. Unstable Soil Aggregates Caused By

      1. Wetting And Drying
      2. Freezing and Thawing
      3. Root Pressures
      4. Fungi With Hyphae That Encompasses Soil Particles
      5. Soil Tillage

    3. Cementing By ... When Unstable Soil Aggregates Are Brought Together

      1. Clay
      2. Organic Matter
      3. Iron Oxides
      4. Aluminum Oxides

    4. Importance: Good Soil Structure = Good Permeability

      1. Less Erosion
      2. Decreases Runoff
      3. Enhances Root Growth
      4. Better Water Holding Capacity
      5. Better Drainage

    5. Improvement

      1. Avoid Clodding and Compaction - Do Not Till When Wet
      2. (Ca+Mg)/Na Ratio - Lime Properly and Help Soil and Organisms
      3. Add Organic Matter - Grow and Till In Grasses and Legumes
      4. For Neccessary N Microorganisms (Rhizobium) - Grow Legumes
      5. Turn Under Crop Residues For Organic Matter

  6. Soil Consistence

    1. Cohesion - Plasticity

    2. Adhesion - Stickyness

    3. Type of Clay - Soil Consistence

    4. Atterberg Limits - Lab Tests

    5. Plasticity

      1. Determination of Plasticity: Press Into Ribbons By Pressing Soil Between Forefinger and Thumb

      2. Importance: Hold Water Well - May or May Not Hold Great Amounts of Nutrients, Depends on Kaolinite

    6. Stickyness

      1. Determination of Stickyness: Will Wet Soil Stick To Fingers?

        1. Sticky = Montmorillonite
        2. Not So Sticky = Kaolinite

      2. Importance: High in Water and Nutrients - Montmorillonite Clays

  7. Soil Color

    1. Organic Matter - Black

    2. Heat/Temperature - Dark Soil Absorb More Heat

    3. Parent Materials - Felsic Are Light While Mafic Are Dark

    4. Drainage

      1. Red - Yellow: Oxidized Fe
      2. Blue - Gray: Reduced Fe
      3. In Soils

        1. Well: no gray throughout
        2. Moderate: gray in lower B
        3. Somewhat Poor: gray in upper B
        4. Poor: gray throughout

  8. Soil Temperature

    1. Controlled By Radiant Energy

      1. Near Surface The Teperatures Are Affected By

        1. Air Temperature
        2. Vegetation
        3. Soil Moisture/Drainage
        4. Soil Color

      2. Deeper - Seasonal Changes
      3. Deepest - Determined By the Annual Temperature

    2. BioActivity

      1. Above 5oC (40oF) Increases
      2. 0oC (32oF) to 5oC (40oF) Suspended
      3. At 0oC (32oF) Ceases

    3. Germination

      1. From 13oC (55oF) To 38oC (100oF) Increases
      2. Below 13oC (55oF) Slow

  9. Soil Permeability

    1. Permeability = Interconnected Pore Space

    2. Importance = Air, Water, Organisms Can Move

    3. Pore Space = % By Volume or Volume of Air or Water That can be Held By the Soil

    4. Soil Bulk Density = Weight or Mass/Volume

    5. Soil Percolation Rates: After The Soil Percolation Test Pit (6 to 12 in square by 18 to 24 in deep) Has Been Saturated (Overnight) Take Measurements

    6. Soil Texture

      1. Sands: May Have Little Pore Space But Good Permeability
      2. Clays: May Have Much Pore Space But Poor Permeability

    7. Soil Drainage

      1. Drainage: If Soil is Well Drained, The Soil Is Better Oxidized
      2. Problem: The Soil May Have Good Permeability But Beacause of Some Other Factor (Slope, Location, etc.) It May Be Poorly Drained

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