Soils Exam 2

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  1. Which is static, texture or structure?
    Texture is static, structure is dynamic
  2. What are the top two coloring agents?
    • (1) Organic matter (darkens soil)
    • (2) FeO2 (red/orange/yellow)
  3. Size of Sand
    2-.05 mm
  4. Size of Silt
    0.05-.002 mm
  5. Size of clay
  6. Specific surface
    the amount of particle surface area exposed and available as a site for chemical and physical processes per unit mass or volume of soil
  7. Specific surface affects:
    • (1) Adsorption/retention of water
    • (2) Adsorption of chemicals
    • (3) Area for chemical reactions
    • (4) Aggregation
    • (5) Microbial colonization
  8. Specific surface (As) is a function of which two things?
    • (1) Particle size
    • (2) Mineralogy
  9. Characteristics of Coarse soils
    Holds less water/nutrients, not very erosive, very permeable, may compact to form hardpan
  10. Characteristics of fine soils
    holds large amounts of water/nutrients, erosion, slow permeability, and may shrink/swell.
  11. Soil structure
    Structure is the arrangement of primary sand, silt, and clay particles into secondary aggregates called peds or structural units which have distinct shapes are easy to recognize.
  12. Soil structure: structureless
    • massive
    • single grained
  13. Soil structure types
    Granular, block, platy, columnar, prisimatic
  14. Columnar vs prismatic
    columnar is rounded on top, prismatic is flat on top
  15. Soil structure grade
    scale from 0-3 (0 being structureless)
  16. What causes soil structure to develop?
    • (1) wetting/drying
    • (2) Plant activity and root pressure
    • (3) Microorganisms
    • (4) Cementing by clay, organic matter, iron and aluminum compounds
  17. Management of soil structure involves
    • (1) Minimizing soil disturbance
    • (2) Timing disturbance
    • (3) Add the proper amounts of lime and fertilizer (plant growth)
    • (4) Maintain or increase organic matter contents of Ap horizon.
  18. Slaking is
    the breakdown of large, air-dry soil aggretates into smaller microaggregates when suddenly immersed in water.
  19. Particle density (Dp)
    Dp = mass of dry soil/soil solids - volume of soil solids
  20. Bulk density
    An index of compaction.  Increased compaction, increased Db.  Larger particle size, increased Db.

    Db = mass of dry soil - bulk V of soil material

    Db = mass soil solids - (V of soil solids + volume of pores)
  21. What farm operation may cause compaction?
    Extensive cultivation
  22. As bulk density increases...
    • (1) Soils become more compact
    • (2) Soil strength increases
    • (3) pore space decreases
  23. PSp
    percent pore space; F*100
  24. Porosity (f)
    a soil physical property which indicates how much of the bulk volume of the soil is occupied by pores.

    f = Vpores + Vtotal
  25. Macropore characteristics
    • >0.08 in diameter 
    • Influenced by soil structure
    • allow for mvt of ai and water
    • normal field conditions contain air
  26. Types of macropores
    • (1) Interparticle
    • (2) Tubular 
    • (3) Planar voids (cracks between peds)
  27. Micopores
    • Influenced by soil texture
    • <0.08 mm in diameter
    • mesopores are included here
    • tend to hold water
    • less air in micropores
    • less air mvt; water mvt slow
  28. Soils with a high porosity can benefit upland crop culture due to:
    • can accomodate a large V of air and water
    • Air and water mvt may be effective
    • Limited or no problem of root penetration
    • Soil is relatively less prone to erosion
  29. Soil consistence:
    • describes the ease with which a soil can be reshaped or ruptured
    • refers to the degree of plasticity and stickiness of the soil
    • soil consistence is affected by the type and amount of clay in the soil (high clay content means high stickiness)
  30. Soil strength
    the capacity of a soil mass to withstand stress without rupturing or becoming deformed
  31. Plastic Limit
    An atterberg limit.  Water content (%) beyond which the soil will transform into a malleable, plastic mass and cause additional swelling; never disturb soil when the moisture content is above the plastic limit
  32. Liquid Limit
    Water content (%) when water transforms into a viscous liquid that will flow when jarred
  33. Coefficient of liner extensibility
    quantifies the expansiveness of a soil
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Soils Exam 2
2015-02-28 22:02:45

soils exam 2
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