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What does it mean when you can make a long ribbon ??

What does it mean when you can make a long ribbon ??. High clay content !. Sandy clay, silty clay or clay. http://www.fao.org/docrep/field/003/AC172E/AC172E04.htm. An alternative method of “texture by feel”. Start with a ball of soil about 3 cm in diameter.

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What does it mean when you can make a long ribbon ??

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  1. What does it mean when you can make a long ribbon ?? High clay content ! Sandy clay, silty clay or clay http://www.fao.org/docrep/field/003/AC172E/AC172E04.htm

  2. An alternative method of “texture by feel” Start with a ball of soil about 3 cm in diameter http://www.fao.org/docrep/field/003/AC172E/AC172E04.htm

  3. Ball throwing method The texture of soil can be inferred by the way a ball of soil acts when it is thrown at a hard surface such as a wall or a tree. Throw a ball of soil to a tree or wall 3 m away. If the soil is good only for splatter shots when either wet or dry, it has a coarse texture (loamy sand). If there is a “shot gun” pattern when dry and it holds its shape against medium range target when wet, it has a moderately coarse texture (sandy loam). If the ball shatters on impact when dry and clings together when moist but does not stick to the target it has a medium texture (loam, sandy clay loam, silty clay loam). If the ball holds its shape for long - range shots when wet and sticks to the target but is fairly easy to remove it has a moderately fine texture (clay loam). If the ball sticks strongly to the target when wet and becomes a very hard missile when dry, it has a fine texture (clay) :->. http://www.fao.org/docrep/field/003/AC172E/AC172E04.htm

  4. Does this soil have a high clay content? Not necessarily !! Color can be misleading!! Soil consistence is a better indicator of clay than color High clay soils tend to be very cohesive and adhesive when wet and hard when dry !

  5. Clay affects many soil properties Brady and Weil, 2002

  6. Clay affects many soil properties Brady and Weil, 2002

  7. Clay affects many soil properties Brady and Weil, 2002

  8. Expansive soils ~ 10 billion dollars of structural damage caused by expansive soils in the US each year

  9. Expansive soils in the central US Abundant clay with high swelling potential Less than 50% clay with high swelling potential Abundant clay with slight to moderate swelling potential Less than 50% clay with slight to moderate swelling potential Little to no swelling clay

  10. Special design features for expansive soils Brady and Weil, 2002

  11. Understanding expansive soils Plasticity index Coefficient of linear extensibility VPL - VSL ----------- VPL low high Moisture content Brady and Weil, 2002

  12. WIU (%) Clay content 0-12” Textural class 0-12” Where is the clay in central McDonough Cty ??

  13. (%) Organic matter content 0-12”

  14. Soils with more clay tend to accumulate more C C content (%) Clay content (%) (Körschens et al., 1998)

  15. More OM is needed to stabilize fine textured soils 16 % clay 39 % 49% 39 % 49% 16 % clay Adapted from Russell (1973)

  16. Cation exchange capacity 0-12” (centimols/kg)

  17. What is the other source of charge ? Relationship between SOM and CEC Organic Contribution to CEC Total CEC } clay http://www.grdc.com.au/growers/res_summ/cso00029/part3_2_1.htm

  18. (cm) Plant available water 0-60”

  19. Impact of clay on plant available water Available water Brady and Weil, 2002

  20. Why do fine textured soils normally have lower bulk densities than coarse textured soils ? (g/cm3) Bulk density 0-12” Brady and Weil, 2002

  21. If bucket A contains a high clay soil and bucket B a low clay soil, which bucket is likely to weigh the most? B A

  22. Why 2 microns ???? Classifying soil particle sizes Coarse sand Brady and Weil, 2002 In most but not all classification systems, clay is defined as < 2 microns

  23. Very small particles have special properties What is a colloid? Colloids stay in suspension 2 microns 1nm – 1000nm Brady and Weil, 2002

  24. Impact of particle size and shape on surface area : volume ratio What normally happens to particles with high surface area to volume ratios ? They dissolve ! Diameter

  25. Relationship between particle size and mineralogy http://www.fao.org/docrep/field/003/AC172E/AC172E04.htm

  26. Primary minerals congruent chemical weathering physical weathering incongruent chemical weathering HCO3- K+ Cl- Ca+2 Na+ SO4-2 sand and silt dissolved salts K+ secondary minerals

  27. Clay particles are made of very insoluble materials !

  28. How did this happen ?? Eluviation Illuviation Foth, 8th ed.

  29. Dry soil at the end of an extended dry period http://edafologia.ugr.es/iluv/media/origen1.gif

  30. Rain water rapidly infiltrates the surface horizon http://edafologia.ugr.es/iluv/media/origen2.gif

  31. Some clay particles disperse in water filled pores http://edafologia.ugr.es/iluv/media/origen3.gif

  32. Suspended clay moves downward through macropores to deeper, drier horizons http://edafologia.ugr.es/iluv/media/origen4.gif

  33. Capillary action moves water outward into micropores http://edafologia.ugr.es/iluv/media/origen5.gif

  34. A thin “skin” of oriented clay particles begins to accumulate on the walls of macropores http://edafologia.ugr.es/iluv/media/origen6.gif

  35. Oriented clay particles coat the walls of dry macropores http://edafologia.ugr.es/iluv/media/origen7.gif

  36. Many years go by… The process repeats itself over and over… causing illuvial clay skins to slowly increase in thickness http://edafologia.ugr.es/iluv/media/origen8.gif

  37. Where did this clay come from ? Clay skins Translocation Alteration Neoformation http://edafologia.ugr.es/iluv/media/rec1.gif

  38. Soil forming processes Primary  Secondary minerals clay minerals TRANSFORMATIONS Adapted from Stewart (1990)

  39. a primary mineral 2NaAlSi3O8 +9H2O + 2H+ 4H4SiO4 2Na+ H4Al2Si2O9 Kaolinite a secondary clay mineral Soluble leachates

  40. Silicate minerals make up 92% of the earth’s crust !

  41. Plagioclase Feldspar What do these minerals have in common ? Orthoclase Feldspar Quartz They are all silicate minerals ! - different configurations of the same building blocks Pyroxene Amphibole Muscovite

  42. Quartz Muscovite Dominant silicate mineral in sand fraction Example of a primary phyllosilicate mineral http://espm.berkeley.edu/classes/espm-121/soilmineralogy.html

  43. Building blocks of phyllosilicate clay minerals http://pubpages.unh.edu/~harter/crystal.htm Oxygen atoms at each corner and an aluminum atom in the center Aluminum octahedron Silicon tetrahedron Why is this structure called an octahedron?

  44. Assembling the building blocks into sheets Tetrahedral sheet Octahedral sheet

  45. 1:1 configuration Hydrogen atoms hydroxyl groups Octahedral sheet 1:1 layer * * shared oxygen atoms * Tetrahedral sheet http://pubpages.unh.edu/~harter/crystal.htm

  46. 2:1 configuration Tetrahedral sheet shared oxygen atoms Octahedral sheet 2:1 layer * * * * * * shared oxygen atoms Tetrahedral sheet http://pubpages.unh.edu/~harter/crystal.htm

  47. http://pubpages.unh.edu/~harter/crystal.htm Non-expansive ! Hydrogen bonding of 1:1 layers

  48. Expansive 2:1 layers Bentonite Brady and Weil, 2002

  49. Non-expansive 2:1 layers K+ Brady and Weil, 2002 Illite

  50. Different types of phyllosilicate minerals Brady and Weil (2002)

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