SOIL GENESIS, PHYSICAL, CHEMICAL AND COLLOIDAL PROPERTIES OF SOIL

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SOIL GENESIS, PHYSICAL, CHEMICAL AND
COLLOIDAL PROPERTIES OF SOIL

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Soil Genesis

• Genesis means origin. It means how soils are
  developed. Mostly soils are developed by
  weathering of minerals. Soil genesis includes
  soil forming factor and soil forming process.
• Soils from mineral materials are developed by
  the dynamic forces of climate and the action of
  plants and animals (biosphere) as modified by
  topography (lay of the land) over time (years).

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• I- RESIDUAL PARENT MATERIALS
• Parent material formed from weathered minerals
• Weathering of bed rocks
• R.P.M. is formed on relatively level topography
• ORIGIN OF PARENT MATERIAL
• may be from rocks
• Igneous
• Sedimentary
• Metamorphic rockschemical composition changed by
  heat

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• II- TRANSPORTED PARENT MATERIAL formed from
  weathered rocks that have been moved to another
  location by water, wind, ice or gravity.
• III- CUMULOSE PARENT MATERIAL
• Could be called residual parent material
• Because they have been formed in place, in
  another sense, they are not residual because they
  did not develop from underlying bed rocks.
• Parent material of organic soils (cummulose) are
  mostly plant residues preserved by excessive soil
  wetness.

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SOIL FORMATION FACTORS

• A soil is generated when the active factors of
  climate and biosphere interact with passive
  parent material and modified by passive
  topography over neutral time.
• Parent material
• Climate
• Organisms
• Topography
• Time

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Soil Forming Processes

• Boul et al. (1980). Lists a number of
  important soil forming processes into four
  categories i.e. additions, losses, transfers and
  transformation with in a soil body. Further these
  are classified as
• General processes
• Specific processes

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• General Soil Forming Process
• Eluviation movement of material out (e.g., E
  horizons also A horizons).
• Illuviation movement of material in (B horizons)
  
• Decalcification removal of calcium carbonate
• Lessivage downward migration and accumulation of
  clay, producing an argillic or clay-enriched
  horizon.

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Fullerton Series, Typic Hapludult, showing clay,
Fe accumlation in the Bt horizon.
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Pedoturbation

• Pedoturbation is the process of soil mixing by
  fauna and flora and physical churning and cycling
  of soil materials. It may invert soil layers. It
  has following types
• Faunal Pedoturbation
• Floral Pedoturbation
• Agrilli Pedoturbation

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Specific Soil Forming processes
Calcification Weak eluviation and
formation of secondary calcium
carbonates in sub soil horizons and leads
to formation of the chernozemic soils.
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Podzolization

• Fe, Al, and organic matter accumulate in the
  illuviated spodic (Bh or Bs)
• Fe and Al leach from eluviated albic (E) horizon
• Dominant in the boreal climatic zone,
• Also occur in southeast coastal plain of US
  (Aquods, Groundwater Podzols) an
• Giant podzols'' with extremely thick E and Bs
  horizons occur in the tropics

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Other Specific Soil Forming Process

• Salination
• Alkalization
• Desalination
• Dealkalization

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Spodosol a result of podzolization (called
Podzols in other classification systems besides
the US)
Photo of soil profile
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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CLIMATE AND SOIL GENESIS

• SOIL ORDERS
• Entisols (any climate, young parent material)
• Aridisols (dry climate)
• Histosols (any climate where surface water is
  abundant)
• Oxisols (tropical climate)
• Ultisols (humid, sub-tropical climate)
• Mollisols Vertislos (calcareous plant material)
• Alfisols Inceptisols (not closely related with
  climate)
• Spodosols

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Aridisol Entisol
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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Gelisol Histosol
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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Inceptisol Mollisol
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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Oxisol Spodosol
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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Ultisol Vertisol
Photos courtesy of USDA NRCS, National Survey
Center http//www.statlab.iastate.edu/soils/photog
al/orders/soiord.htm
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Topography and soil genesis

• Determines runoff water
• Controls the amount of soil material removed and
  relocated
• Affects deposition and soil texture
• Affects the vegetation

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Biosphere and soil genesis

• Flora Fauna
• Active Factor
• Effect of plants
• Effect of animals

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Time and soil genesis

• Affects soil genesis
• Neutral Factor
• Time influences all other factors

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Soil Physical Properties

• Soil Texture
• Provides general information regarding the
  amount of sand, silt and clay
• Soil Structure
• Arrangement of soil particles to form
  aggregates

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Soil Physical Properties

• Soil Consistence
• Relative cohesive strength of aggregates to
  resist rupture and deformation.
• Particle density
• Weight of individual soil particle in relation
  to water
• Bulk density
• Weight of volume of soil in relation to equal
  volume of water

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Soil Physical Properties

• Soil Color
• Measured in terms of hue, value and chroma

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Soil Physical Properties

• SOIL TEMPERATURE
• Bacteria (25-30 oC)
• Fungi (37 oC)
• N Fixing Organisms (36 oC)
• Actinomycetes (55-59 oC)

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Soil Chemical and colloidal Properties

• Organic Matter
• Provides a generalized indication of the
  relative fertility status of soil, promotes great
  water retention, aeration and fertility.
• Soil pH
• An index of the relative acidity and
  alkalinity of the soil.
• Buffering
• Resistance to change in pH

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Soil Chemical and Colloidal Properties

• Soil Salinity Range
• An index of salt content
• Cation Exchange Capacity
• Relative measure of soil potential to retain
  added nutrients