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Laterization of Tropical Soils

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Laterization is the weathering process of tropical soils in ... This soil taxonomy refers to soils of tropical rain forest 15 to 25 degrees from the equator. ... – PowerPoint PPT presentation

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Title: Laterization of Tropical Soils


1
Laterization of Tropical Soils
  • Tyson Wine
  • Envir 315
  • Professor Terry Swanson

2
Laterization of Tropical Soils
  • Laterization is the weathering process of
    tropical soils in which soil and rocks are
    depleted of silica and bases (acidic) while being
    enhanced with aluminum and iron oxides.
  • This process forms what is known as a laterite,
    from the Latin later meaning brick or tile.

3
Laterization
  • This image is what is known as an ultisol.
  • Laterization forms these deep red to bright
    orange-red soils because they are high in iron
    content..
  • These soils are often acidic and lack much
    organic matter.

4
Laterization
  • These soils form in hot, rainy locations,
    especially the tropics, where chemical reactions
    from weathering are rapid.
  • Decomposition and leaching occur quickly.
  • The heavy rains, porous underlying rock, and hot
    climates make for high weathering and ultimately
    depleted soils which can harden into laterites.

5
Laterites
  • Also classified as oxisols.
  • Oxisols are defined as containing no more than
    10 weatherable minerals (at any depth).
  • The weatherable materials have already been
    weathered.

6
Oxisol
These oxisols are classified as such by the USDA.
This soil taxonomy refers to soils of tropical
rain forest 15 to 25 degrees from the equator.
7
Laterization
  • Iron and aluminum rich oxides concentrate at or
    near the topsoil.
  • Bases (Ca, Mg, K) are available from the
    vegetation forms a lack of humic acid.
  • Iron and aluminum oxides are insoluble without
    humic acid and concentrate.
  • When these high concentrations of oxides are
    exposed to air, they harden through desiccation
    to form laterites.

8
Laterization in Tropical Rainforests
  • Rainforests were originally considered to be high
    in nutrients, but are now realized to survive off
    of the decomposing debris on the forest floor,
    not oxisols.
  • Oxisols lack of soluble minerals makes them
    infertile, making it virtually impossible for
    plants or trees to form without the presence of
    plant and tree debris.

9
Coping with Laterization
10
Coping with Laterization
11
Feedbacks
  • Tree roots extend laterally up to 25 feet,
    providing structure and preventing erosion.
  • The elimination of these roots allows for greater
    runoff and erosion.

12
Deforestation
  • Since the plants and trees of tropical
    rainforests rely on decomposing organic matter
    for nutrients, deforestation eliminates the
    source of their nutrients.
  • Oxisols do not contain high nutrients and do not
    allow for the regrowth of an extensive forest.
  • In addition, many hardwood trees depend on
    animals for seed dispersal. Elimination of
    animals thus prevents many rainforest flora from
    germinating.
  • Also, the loss of the forest canopy results in
    many seedlings not being able to germinate due to
    temperature or other variations in microclimatic
    conditions.
  • Lastly, the loss of mycorrhiza leaves many
    seedlings without the ability to fix nitrogen and
    assist in nutrient transport.

13
Deforestation in Madagascar
14
Deforestation
15
Deforestation
16
Deforestation
  • In addition, the lack of a canopy allows for the
    soil to be exposed to the sun and wind, allowing
    farther evaporation (desiccation) to harden the
    soils more.
  • Another positive feedback that results from this
    occurs due to reduced infill and increased
    runoff, leading to faster removal of water and
    nutrients and increasing the laterization effect.

17
Deforestation
18
Slash and Burn Agriculture
  • The slash and burn method of deforestation
    provides enough nutrients to support agriculture
    for a few years.
  • Since the soil contains no nutrients, these soils
    are completely used up within a few years, after
    which they are virtually useless.

19
Permanence
  • Laterization is irreversible due to feedbacks and
    rapid rate of erosion. The end result is hard
    soils incapable of supporting agriculture, let
    alone the forests that survived for millennia.

20
References
  • Butler, Rhett A. Soils and Nutrient Cycling.
    ltwww.rainforests.mongabay.comgt. 2008.
  • ThinkQuest Team 26634. Impact of Deforestation
    on Laterization. 1999. ltlibrary.thinkquest.orggt.
  • Ritter, Michael E. Soil Forming Processes. The
    Physical Environment an Introduction to Physical
    Geography. lthttp//www.uwsp.edu/geo/faculty/ritter
    /geog101/textbook/title_page.htmlgt. 2009.
  • Desertification. Wikipedia, the free
    encyclopedia. 2009. ltwww.wikipedia.comgt.
  • Butler, Rhett A. Amazon Destruction. Mongabay.
    ltwww.rainforests.mongabay.comgt. 2008.

21
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