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11.8: Review and Additional Resources

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    Figure \(\PageIndex{1}\)

    Review and assess your learning. Start with the "Important Terms and Concepts" to ensure you know the terminology related to the topic of the chapter and concepts discussed. Move on to the "Review Questions" to answer critical thinking questions about concepts and processes discussed in the chapter. Finally, test your overall understanding by taking the "Self-assessment quiz".

    Important Terms and Concepts

    • Parent material
      the material that soil develops from, and may be rock that has decomposed in place, or material that has been deposited by wind, water, or ice
    • Soil forming factors
      parent material, climate, topography, organisms, and time
    • Soil horizon
      different colored layers; form as a result of the four horizon development processes, additions, transformation, translocation, and removal
    • O horizon
      primarily composed of organic matter; filled with nutrients and has strong soil moisture retention
    • A horizon
      the beginning of the true mineral soil; organic material mixed with inorganic products of weathering; typically dark colored due to the presence organic matter
    • E horizon
      generally light-colored with eluviation being the dominant process; Leaching is active in this horizon
    • B horizon
      accumulation of fine material leads to the creation of a dense layer
    • C horizon
      the soil parent material, either created in situ or transported into its present location
    • Soil profile
      All the horizons taken together
    • Humus
       dark brown, nutrient-rich material made from decomposed leaves and plant roots.
    • Material addition
      materials that are transported into the location where a soil is forming
    • Material transformation
      occur by chemical and biological processes acting on them
    • Material translocation
      involves the movement of soil-forming materials through the developing soil profile
    • Material removal
      the materials are completely removed from the soil profile
    • pH scale
      how hydrogen ion concentration in the soil is measured
    • Bulk density
      the mass per unit volume including the pore space
    • Soil structure
      the way soil particles aggregate together into peds.
    • Soil texture
      refers to the relative proportion of sand, silt and clay size particles in a sample of soil
    • Ped
      soil structure forms; come in a variety of shapes depending on the texture, composition, and environment
    • Granular structure
      crumb structures, look like cookie crumbs. They tend to form an open structure that allows water and air to penetrate the soil
    • Platy structure
      looks like stacks of dinner plates overlaying one another. Platy structure tends to impede the downward movement of water and plant roots through the soil
    • Physical weathering
      aka mechanical weathering; the breakdown of large pieces of earth material into smaller ones
    • Chemical weathering
      breaks down earth material by chemical alteration
    • Laterization
      occurs in the hot, rainy tropics where chemical weathering proceeds rapidly
    • Podzolization
      The E horizon is heavily leached and basically composed a of light colored layer of sand. The upper portion of the B horizon is stained reddish color from the accumulation of sesquioxides. The profile gets lighter in color as depth increases. 
    • Calcification
      Soil tends to be rich in organic matter and high in soluble bases. The B horizon of the soil is enriched with calcium carbonate
    • Gleization
      occurs in regions of high rainfall and low-lying areas that may be naturally waterlogged. Bacterial activity is slowed, inhibiting the decomposition of dead vegetation. Peat is found in the upper portion of the soil. the soil has a black to bluish - gray color.
    • Salinization
      occurs in warm and dry locations where soluble salts precipitate from water and accumulate in the soil. Salt may also accumulate in soils from sea spray.
    • Oxisol
      Chemical weathering in the presence of warm temperatures combined with heavy rainfall creates a soil rich in iron and aluminum oxides. A rich diversity of decomposers, rapid uptake by vegetation, and heavy precipitation quickly removes nutrients from the soil. What is left is a nutrient poor soil, not well-suited for agriculture. Cleared of vegetation, the exposed surface is easily eroded.
    • Ultisol
      Highly weathered soils, they are often red/yellow in color. Found in the moister portions of the Humid Subtropical climate, they have a illuvial clay layer
    • Alfisol
      Eluviation is moderate and base status is fairly high; well-developed and contain a subsurface layer of clay. Having a favorable moisture balance and good fertility, they are very productive soils for agriculture.
    • Spodosol
      Surface litter breaks down in the presence of water to form a weak organic acid. Acidic soil water removes base ions in solution to create an acidic soil. Easily dissolved materials are leached from surface layers leaving behind the most resistant material creating an ashy-gray near-surface layer. Layers at depth are stained with iron and aluminum oxides.
    • Mollisol
      well-known for their dark brown to black organic rich surface layers; have a granular structure and soft consistency when dry. Rich in calcium and others nutrients, and generally posses high moisture retention. Calcium nodules are found near the base of the soil as calcium carbonate precipitates out of soil water.
    • Entisol
      soils lacking horizons because their parent material has only recently accumulated. Also form where the parent material is quartz sand, in which horizons do not easily form. 
    • Inceptisol
      soils just starting to show horizon development
    • Histosol
      have a very high content of organic matter in the dark upper layer of the profile. Form in places where organic matter is slow to decompose and thus accumulates over time such as bogs and swamps.
    • Aridisol
      typically light in color as there is little organic matter. A negative moisture balance in these soils inhibits eluviation. Calcification and salinization are acting in these soils. Soil horizons are weakly developed and sodium is often high in concentration.
    • Andisol
      Soils developing in parent material containing at least fifty percent volcanic ash; support a dense natural cover in moist climates.
    • Vertisol
      Dark black soils rich in expandable clay minerals. The clay readily swells upon wetting and shrinks when dried. Surface fragments fall into the cracks and are "swallowed" when the soil swells upon wetting. The soil then develops an "inverted profile" with organic material that is typically located near the surface of the profile is now found at depth.

    Review Questions \(\PageIndex{1}\)

    Which soil orders lack noticeable horizons?


    Entisols lack noticeable horizons as parent material has not undergone significant weathering processes.  On the other hand, oxisols may be so strongly weathered that visually distinguishing horizons can be difficult.

    Which soil order has the highest organic content?


    Histosols are noted for high organic content. Peat can be mined from histosols.

    Describe the various soil forming processes.


    Soil forming processes are what determine the type of soil that forms. Podzolization - Cool, humid environments; needle leaf forest cover common. Leads to the development of soils that are acidic, have an ash-grey E-horizon. Spodosols. Laterization - warm, humid environments; broadleaf evergreen forest cover. Creates highly oxidized soils that are red/yellow in color. Oxisols; Ultisols. Calcification - warm, dry environments; grass cover. Creates soils rich in calcium carbonate; high base status. Salinization - warm, dry environments. Creates soils containing soluble salts.

    Which vegetation biome is associated with mollisols?



    In which soil order might you find a subsurface layer of calcium carbonate?



    Which soil order forms an "inverted soil profile"?



    Which soil orders are associated with midlatitude temperate forests?



    What impact do broadleaf deciduous trees have on the nutrient status of soils?


    Broadleaf deciduous forest increase the nutrient base status of soil. A constant cycling of nutrients between the soil and tree occurs through decomposition of leaf litter and root uptake.

    How does soil particle size influence field capacity, infiltration, and permeability?


    Fine textured soils (small particle size) have more total pore space per unit volume than does coarse textured soils (large particle size). Fine textured soils have high field capacity than coarse textured soils. Coarse textured soil has larger, better connected pore space yielding greater infiltration and permeability compared to fine textured soil.

    What is soil texture and why is it important?


    Soil texture is the relative proportions of sand, silt, and clay size particles. Soil texture effects such processes as infiltration, permeability, and field capacity.

    Self-Assessment Quiz \(\PageIndex{1}\)

    1. The zone of illuviation is commonly the 
      1. O horizon
      2. A horizon
      3. B horizon
      4. C horizon
    2. A soil texture with 30% Clay, 30 % silt, and 40% Sand is classified as a
      1. loam
      2. clay loam
      3. silty clay loam
      4. sandy clay 
    3. Which of the following soil structures would impede the infiltration of water the most?
      1. Platy
      2. Blocky
      3. Crumb
      4. Columnar
    4. Which of the following soil orders is most associated with broadleaf deciduous temperate forests?
      1. Spodosol
      2. Aridisol
      3. Mollisol
      4. Alfisol
    5. Soil profiles are likely to be the least developed
      1. at the top of a hill
      2. at the middle of a hill slope
      3. a slight distance ahead of a hill slope
      4. none of the above as hill slope site has nothing to do with soil development
    6. Which of the following soil horizon processes creates the acidification of soils by the break down of organic matter?
      1. Additions
      2. Removals
      3. Transformation
      4. Transfer 
    7. Which of the following is not a soil forming factor?
      1. Time
      2. Organisms
      3. Parent material
      4. Season

    climate map

    1. Which of the following soil forming processes is likely occurring at letter L
      1. Calcification
      2. Laterization
      3. Podzolization
      4. Acidification
    2. Which soil would I most likely find at location E
      1. Spodosol
      2. Ultisol
      3. Mollisol
      4. Aridisol
    3. Which soil would I most likely find at location C
      1. Spodosol
      2. Ultisol
      3. Mollisol
      4. Aridisol
    1. C
    2. B
    3. A
    4. D
    5. B
    6. C
    7. D
    8. A
    9. B
    10. A

    Additional Resources

    Use these resources to further explore the world of geography

    Connections"How to green the world's deserts and reverse climate change | Allan Savory" TED Talk

    Web Sites


    web site icon Natural Resources Conservation Service

    web site icon States Soils - NRCS


    This page titled 11.8: Review and Additional Resources is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Michael E. Ritter (The Physical Environment) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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