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An Overview of Andisols - ResearchGate

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					AN OVERVIEW OF ANDISOLS
         LILLY SANOVIA
     OGLALA LAKOTA COLLEGE
       NOVEMBER, 2011
           WHAT IS AN ANDISOL?

• USDA soil taxonomy classifies an Andisol as a soil
  formed on pyroclastic parent materials.
• Andisols contain a significant percentage of
  volcanic glass and colloidal materials.
• In the FAO soil classification, Andisols are called
  Andosols.
                 OCCURRENCE

• Andisols are found over less than 0.8% of the Earth’s
  surface.
• Occur most commonly in the Pacific Ring of Fire
  due to the volcanism present there.
• Largest occurrences in Chile, Ecuador, Columbia,
  Mexico, Japan and Java.
                     TWO IMPORTANT PROPERTIES

• The presence of extractable aluminum and iron
• Short-range-order clay minerals such as allophane
  and imogolite




 Source: http://www.mindat.org/min-139.html   Source: http://www.mindat.org/photo-143668.html
             PARENT MATERIAL
• Parent materials include volcanic ash and other
  material ejected during volcanic explosion
  (pyroclastics)
• Volcanic ash consists of glassy materials with
  detectable amounts of aluminum and silica
• Volcanic ash is highly soluble and amorphous
  (no well-defined crystalline structure)
                       WEATHERING
• Weathering of pyroclastics forms short-range-
  order compounds
• The most detectable of these in an Andisol
  are allophane and imogolite
• Weathering of these parent materials also
  produces other non-crystalline
  aluminosilicates and ferrihydrite.




           Source: http://webmineral.com/specimens/photos/Ferrihydrite.jpg
                    TIME
• Weathering of pyroclastic parent materials
  occurs faster than most other parent materials.
• As a result, many Andisols are relatively young
• Weathering is much slower in arid
  environments.
• As a result, Andisols in arid environments tend
  to be older than Andisols in wetter
  environments.
                 HUMIFICATION
• Aluminosilicates stabilize humic
  acids, causing them to
  accumulate (humification).
• This process causes the soil to
  darken on the surface
  (melanization).
• These complexes of humic acids
  and aluminosilicates are not very
  soluble
• As a result, they tend to
  accumulate on the soil surface,
  causing a thick, dark horizon
               CLASSIFICATION OF ANDISOLS

• Andisols are classified as having less than 25%
  organic carbon.
• Must also meet one or more of these conditions:
 •   Extractable percentage of aluminum/iron of 2% or more
 •   A bulk density of 0.9 g/cm3 or less.
 •   Phosphate retention 85% or more.
 •   The E horizon, if present, will consist of volcanic ash
 •   The B horizon contains SiO2
     • Beaded if there is an E horizon
     • As silcrete if there is an E horizon
                                             EPIPEDON
 • The epipedon is the top
   layer of a soil, commonly
   used for classification.
 • Andisols may have a histic
   epipedon (thin horizon of
   peat or muck)
 • Or a melanic epipedon
   (thick, black horizon)
Source: http://soils.cals.uidaho.edu/soilorders/i/And_04b.jpg
             ANDISOL SUBORDERS

• Aquands – Form in low-lying areas where the water
  table is at or near the soil surface
• Cryands – Form in very cold environments
• Torrands – Form in arid environments
• Xerands – Form in very dry environments
• Vitrands – Young, coarse-textured Andisols with low
  water-holding capacity (due to high presence of
  volcanic glass)
• Ustands – Form in sub-humid environments
• Udants – Form in humid environments. These are the
  most common Andisols.
ANDISOL DISTRIBUTION MAP
                    REFERENCES

• Soils of the Past: An Introduction to Paleopedology,
  Gregory J. Retallack, Blackwell Science Ltd., 2001

• The Twelve Soil Orders, University of Idaho, College
  of Agricultural and Life Sciences, accessed on
  November 16, 2011:
  http://soils.cals.uidaho.edu/soilorders/andisols.htm

• University of Wisconsin – Madison, Department of
  Soil Science:
  http://www.soils.wisc.edu/courses/SS325/soilorders.h
  tm
            ACKNOWLEDGEMENTS

• Dr. Hannan LaGarry
• Oglala Lakota College, Math and Science
  Department

				
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