GY1004 Principles of Physical Geography B

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• GY1004 Principles of Physical Geography B
• Lectures 5-6
• Soils

DEPARTMENT OF GEOGRAPHY
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Soil processes and patterns
The soil process-response system Horizonation
processes Soil types, classification and the
global distribution of soils
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Soil process-response system
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Horizonation processes

• Lessivation
• Leaching
• Translocation
• Mixing

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Lessivation
The finer the texture of the soil, the greater is
the effective surface area exposed by its
particles
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Leaching
Rainwater
Leaf litter
L A Eb Bt C
Organic acids H
Leaching and loss of clay particles, acc. of
organic matter
Clay particles Ca2 Mg2 Na K
Accumulation of clay, iron and bases
Some loss (Ca2 Mg2 Na K)
Some loss to drainage water
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Re-precipitation of CaCO3
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Calcification
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Podsolisation
O A Ea B C
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Pedalfers and Pedocals
PedALFErs Aluminium (Al) and iron (Fe) rich
PedoCAls Calcium (Ca) rich
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Upward translocationSalinisation
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Gleying
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Bivalent (Fe2) Ferrous iron oxide FeO (Reduced
form)
Trivalent (Fe3) Ferric iron oxide Fe2O3
(Oxidised form)
Laterite
Gley soil
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Soil process-response system
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Factors controlling soil development

• Climate
• Parent material
• Vegetation/organic matter
• Topography/relief
• Time

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The influence of climate
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Variation in the character of the weathered
mantle in relation to climate (Strakov, 1967)
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The influence of topography
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Catena
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Zonal soil classification
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Zonal soil classification

• Zonal
• Azonal
• Intra zonal

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Comprehensive Soil Classification System CSCS
Mollisols Aridisols aridus
solum Inceptisols inceptum solum

• Order 12
• Suborder 63
• Great group 250
• Sub group 1,400
• Family 8,000
• Series 19,000
• (USA only)

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The twelve soil orders of the CSCS

• Entisols
• Inceptisols
• Andisols
• Gelisols
• Histosols
• Oxisols

• Ultisols
• Vertisols
• Alfisols
• Spodsols
• Mollisols
• Aridisols

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Summary

• The internal characteristics of a soil depend on
  the operation of horizonation processes
  (leaching, gleying, translocation).
• Fundamental differences in soils are found over
  the Earths surface as a result of differences in
  soil forming processes.

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Summary

• The intensity of these processes is controlled
  by five major factors
• climate, parent, material, vegetation, relief
  and time. These processes operate at a range of
  scales and control both the global and local
  distribution of soil types.

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Summary

• It is possible to define environmental domains
  for different soils and develop zonal models of
  soil development and classification on the basis
  of formative processes.
• The US Comprehensive Soil Classification System,
  however, classifies soils on the basis of their
  physical characteristics, rather than formative
  processes. It is a six-level hierarchical
  classification based on 12 broad soil orders.