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SOIL FORMATION

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Soil Formation

  • The Importance of Soil
    • All life depends on the thin top layer of soil covering the earth’s surface.
    • Topsoil provides:
      • Support
      • Water
      • Air
      • Nutrients

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Weathering: Biological, Chemical, and Physical Processes

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Weathering: Breakdown of Rock near the Surface

Mechanical

  • Geological Activity – abrasion
    • often occurs to rocks in rivers, beaches, or desert areas
  • Glacial Activity
  • Expansion of ice
  • Effects of Temperature

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Erosion – by wind

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Erosion – by water

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Glacier Receding

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Wedging - Frost

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Weathering: Breakdown of Rock near the Surface

Chemical Alteration

  • Carbon dioxide, sulfur dioxide and various nitrogen compounds from the air form acids when dissolved in water. These acids may react with the rock and increase breakdown.

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Chemical Weathering

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Weathering�Breakdown of Rock near the Surface

  • Organic Processes
    • Wedging – Plant Roots

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Wedging - Roots

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What Determines Soil Type

  • P
    • Residual - Transported
    • Least Important Factor for Mature Soils

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Soil Composition

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What determines soil type?

Young Soils/Immature Soils

  • Strongest Influence Is Parent Material

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Mature Soils

  • Strongest Influences: Climate, Vegetation, Drainage

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Soil Formation and Generalized �Soil Profile

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Soil Horizons and Profiles

Soil Profile

  • Suite of Layers at a Given Locality

Soil Horizons

  • Layers in Soil
  • Not Deposited, they are Zones of Chemical Action
  • Layers (horizons) of mature soils
    • O horizon: leaf litter
    • A horizon: topsoil
    • B horizon: subsoil
    • C horizon: parent material, often bedrock

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Principal Soil �Horizons

  • O - Organic (Humus) Often Absent
  • A – Leaching
    • K, Mg, Na, Clay Removed
  • B – Accumulation
    • Absent in Young Soils
    • Distinct in Old Soils
    • Al, Fe, Clay (Moist)
    • Si, Ca (Arid)
  • C - Parent Material

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Soils of the Canada

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Typical Soil Profile (Spodosol)

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Ultisols – Georgia Clay

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Soil Characteristics

  • Physical
    • Texture
    • Porosity
    • Permeability
    • Humus

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  • Chemical
    • pH
      • *You need to know how to fix pH problems
    • Nitrogen
    • Phosphorous
    • Potassium

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  • Porosity - the percentage of interconnected space in rock and soil that can contain water

Permeability – the degree to which the pores in the rock or soil are connected together so that water can move freely

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Main Soil Textures

Soil Type

Texture

Permeability

Porosity

Sand

Gritty

High

Low

Silt

Smooth & Slippery

Med

Med

Clay

Sticky

Low

High

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Soil Formation vs. Soil Erosion

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  • Soil formation
    • Takes hundreds of years to form 1 cm (0.4 inches) of soil

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  • Soil erosion
    • Blown away in weeks or months from plowing and clearing forests – any time we leave the topsoil unprotected

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Topsoil Erosion Is a Serious Problem in Parts of the World

  • Soil erosion
  • Two major harmful effects of soil erosion
    • Loss of soil fertility through depletion of plant nutrients in topsoil
    • Water pollution in nearby surface waters where eroded soil ends up as sediment
      • Kills fish, shellfish
      • Clogs irrigation ditches, reservoirs, lakes, and boat channels
    • Eroded soil may also be polluted with pesticides and fertilizers

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Dust Bowl of the 1930’s

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China’s Dust Storms - 2006

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February 1

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Soil Textural �Triangle Practice �Exercises

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�% Sand % Silt % Clay Texture Name

75 10 15 sandy loam

10 83 7 _______________

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February 2

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Climatic Zone

  • North America is divided into 10 climatic zones, 1 is the coldest, 10 is the warmest.
    • Where are the coldest and warmest climatic zones in Canada?
  • What is our climatic zone in Mill Bay?
    • 8a
  • A plant’s ability to withstand a given climate is called its
    • Hardiness

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http://www.planthardiness.gc.ca/

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Frosts

  • https://tinyurl.com/yc5bbmxc

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  • We need to know how first and last frost to determine our outside growing window.
    • Last spring frost – May 1
    • First fall frost – October 19

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  • These dates determine our general growing season and proper planting and harvesting times
  • Seed packets often have such instructions

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Seed packet info

  • Look at the link below and check out the kind of info on a seed packet

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  • https://gardenerspath.com/how-to/beginners/backs-seed-packets-display-valuable-information-gardener/

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