test 2

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soilscience
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test 2
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2010-10-22 06:31:17
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test2
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  1. pH dependant charge (3)
    • -1:1 clays
    • -Protonation in acidic conditions creates a positive charge on colloid
    • -deprotonation in Alkaline conditions creates a Neg charge on colloid
  2. Isomorphic substitution (3)
    • -Happens during the crystaline formation of 2:1
    • -Happens when cations of a similar radii substitute for each other
    • -Creates a perminate neg charge
  3. Cation Exchange Capacity(3)
    • -Sum of the total of cations a soil can hold
    • -clay surfaces are neg, so they bond to colloid
    • -Measured in cmolc/kg
  4. Osmotic Potential (4)
    • -the force governing water movement from soil to plant roots
    • -The movement of water of a semipermiable surface
    • -water travels from an area of high energy to an area of low energy
    • -Plants use salts to create the energy differencial
  5. Metric Potenital(2)
    • -H20 energy gradient most responsible for capilarity attraction of water to soil solids
    • -Always negative
  6. Field capacity (3)
    • -The amount of water a soil holds after free drainage
    • -48 hours after rain or irrigation
    • --10 kPa to -30 kPa
  7. Saturated hydraulic conductivity (2)
    • -Ksat
    • -The ability of porous material to transmit water
  8. Describe the process of aggregation of clay particles
    • Biological-
    • Bacterial exudates
    • Fungial Hyphae

    • Physical-
    • Polyvalent cations
    • oxide cementing

    Process is Flocculation
  9. Identify the primary driving force for water movement in unsaturated soil and explain the mechanism (6)
    • -Matric potential!!!
    • -moves from areas of high energy to low energy
    • -H20's affinity to solid surfaces (adhesion)
    • -Cohesion
    • -Function of capilary rise
    • - clays transmit h20 further b/c of capilary rise
  10. Given two similarly high clay soils one an oxisol and one a vertisol, Compare Ksat (2) & (2)
    • -Vert would have a low Ksat b/c of the 2:1
    • -The expanding micropores would fill and not drain the water b/c of smectite

    • -Oxisol would have a high Ksat b/c of the good aggregation of the 1:1 clay
    • -psuedosand
  11. When estimating the Volumetric water @ FC one would expect a clay soil to have a FC of____
    Silt____ and Sand_____
    • clay=-30kPa
    • Silt= -20 kPa
    • Sand= -10 Kpa
  12. How do you account for large differences in volumetric water content between clay and sand (2)
    • -Clays hold more h20 b/c of the greater surface area of clays
    • -the adhesion properties of water play a huge role
  13. Why does the plant available water decrease as clay increases?(3)
    • -Due to the attriction of water to clay particles
    • -increased micropores lock up water on its surface
    • -More water in soil but less available to plants
  14. How would you calculate base saturation for a soil? measured in?
    • sum of bases/ ECEC
    • %
  15. How would you determine the Al content of a soil?*
    Al= ECEC-Base/ECEC
  16. How can you determine 1:1 or 2:1 based on CEC and ECEC?(4)
    • -If the CEC and ECEC are very close then it is 2:1
    • -Neg charge

    -Caused by isomorphic substitution

    -Protonation dictates the ph dependant charge
  17. How can use assume the acidity of a soil based on CEC and ECEC
    *CEC is measeured at pH 7*

    When CEC is higher than ECEC then acidic

    • Acidic soils = 1:1=pH dependant
    • More weathering= more acid
  18. Dominate clay mineral on Ustox
    Al/Fe oxides
  19. Source of charge on Colloid surface of Ustox
    pH dependant
  20. Ustox at 4.5 ph, AEC or CEC?
    AEC, more positive charge
  21. What effect does liming have on an acid soil?(3)
    • - The surface charge will become more negative
    • -Removes h+ from soil solution
    • -deprotonation
  22. Given Om and Db find Ov
    Ov=Om *Db
  23. Given Om and Db at FC and at PWP, find the PAW
    • find Ov=Om *Db
    • find the difference between Ov @Fc and Ov @PWP x Depth FOR BOTH FC AND PWP at differnt depths
  24. Discuss denitrification and the role reduction plays in it
    Under staturated conditions the soil is in a reducing environment The N becomes reduced and unavailable to the plants, which causes N deficiencies. Older leaves turn Yellow as N is a mobile nutrient
  25. If a soil has a Om water content of 32%, much would you have to weigh out to ensure you end up with 2000g after ODing?
    2000(.32)=(x-2000/2000)

    • 640= x-2000
    • 2640g = x
  26. Given r and l figure volume of a cylinder
    Pi*r2*l
  27. Figure Db if r= 3.0 cm and l= 15cm and Od is 570
    Pi *3.02cm* 15cm=424.10

    570/ 424.1= 1.3
  28. Given Db 1.3 and Om .179 find the Ov
    Om * Db= Ov

    Ov= .179 * 1.3= .233= 23%
  29. Given Db= 1.3 find porosity unspecified soil
    • Porosity = 1- Db/Dp * 100
    • 1.3 Mg

    1-1.3/2.65 * 100= 51%
  30. Given : Depth 20 cm
    Db 1.15
    Om @ FC=0.35
    Om @ PWP= 0.15

    Find PAW
    Solve for Ov in Each 1st because we need to solve for (Ov @FC) - (OV @ PWP)

    • Ov @ FC= Om * Db= 0.35 * 1.15=.4025
    • Ov @ PWP= Om * Db = 0.15 * 1.15=.1725

    .4025 - .1725=0.23

    0.23 * 20cm= 4.6 cm

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