SOIL GENESIS, PHYSICAL,
CHEMICAL AND COLLOIDAL
PROPERTIES OF SOIL
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).
I- RESIDUAL PARENT MATERIALS:

Parent material formed from weathered
minerals
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Weathering of bed rocks
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R.P.M. is formed on relatively level
topography
ORIGIN OF PARENT MATERIAL:
may be from rocks
1.
Igneous
2.
Sedimentary
3.
Metamorphic rocks—chemical composition
changed by heat
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.
SOIL FORMATION FACTORS
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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
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
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.
Fullerton Series, Typic
Hapludult, showing clay, Fe
accumlation in the Bt horizon.
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
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.
Podzolization
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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
Other Specific Soil Forming
Process
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Salination
Alkalization
Desalination
Dealkalization
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
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)
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Spodosols
Aridisol
Entisol
Photos courtesy of USDA NRCS, National Survey Center
http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Gelisol
Histosol
Photos courtesy of USDA NRCS, National Survey Center
http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Inceptisol
Mollisol
Photos courtesy of USDA NRCS, National Survey Center
http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Oxisol
Spodosol
Photos courtesy of USDA NRCS, National Survey Center
http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Ultisol
Vertisol
Photos courtesy of USDA NRCS, National Survey Center
http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Topography and soil genesis
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Determines runoff water
Controls the amount of soil material
removed and relocated
Affects deposition and soil texture
Affects the vegetation
Biosphere and soil genesis
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Flora + Fauna
Active Factor
Effect of plants
Effect of animals
Time and soil genesis
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Affects soil genesis
Neutral Factor
Time influences all other factors
Soil Physical Properties
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Soil Texture
Provides general information regarding
the amount of sand, silt and clay
Soil Structure
Arrangement of soil particles to form
aggregates
Soil Physical Properties
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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
Soil Physical Properties
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Soil Color
Measured in
terms of hue,
value and
chroma
Soil Physical Properties
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SOIL TEMPERATURE
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Bacteria
Fungi
N Fixing Organisms
Actinomycetes
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(25-30 oC)
(37 oC)
(36 oC)
(55-59 oC)
Soil Chemical and colloidal
Properties
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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
Soil Chemical and Colloidal
Properties
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Soil Salinity Range
An index of salt content
Cation Exchange Capacity
Relative measure of soil potential to
retain added nutrients