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What does it mean when you can make a long ribbon ?? High clay content ! Sandy clay, silty clay.

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Presentation on theme: "What does it mean when you can make a long ribbon ?? High clay content ! Sandy clay, silty clay."— Presentation transcript:

1 What does it mean when you can make a long ribbon ?? High clay content ! Sandy clay, silty clay or clay

2 An alternative method of “texture by feel” Start with a ball of soil about 3 cm in diameter

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) :->.

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

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

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

11 Understanding expansive soils Moisture content Plasticity index Coefficient of linear extensibility V PL - V SL ----------- V PL Brady and Weil, 2002 lowhigh

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

13 Organic matter content 0-12” (%)

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

15 16 % clay39 %49% More OM is needed to stabilize fine textured soils Adapted from Russell (1973) 16 % clay 39 %49%

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

17 Relationship between SOM and CEC Total CEC Organic Contribution to CEC What is the other source of charge ? } clay

18 Plant available water 0-60” (cm)

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

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

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

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

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

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

25 Relationship between particle size and mineralogy

26 physical weathering incongruent chemical weathering congruent chemical weathering sand and silt secondary minerals dissolved salts Primary minerals K+K+ Ca +2 Na + K+ Cl - HCO 3 - SO 4 -2

27 Clay particles are made of very insoluble materials !

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

29 Dry soil at the end of an extended dry period

30 Rain water rapidly infiltrates the surface horizon

31 Some clay particles disperse in water filled pores

32 Suspended clay moves downward through macropores to deeper, drier horizons

33 Capillary action moves water outward into micropores

34 A thin “skin” of oriented clay particles begins to accumulate on the walls of macropores

35 Oriented clay particles coat the walls of dry macropores

36 The process repeats itself over and over… causing illuvial clay skins to slowly increase in thickness Many years go by…

37 Clay skins Where did this clay come from ? Translocation Alteration Neoformation

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

39 H 4 Al 2 Si 2 O 9 2NaAlSi 3 O 8 +9H 2 O + 2H + 4H 4 SiO 4 2Na + Kaolinite Soluble leachates a primary mineral a secondary clay mineral

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

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

42 QuartzMuscovite Example of a primary phyllosilicate mineral Dominant silicate mineral in sand fraction

43 Building blocks of phyllosilicate clay minerals Silicon tetrahedron Why is this structure called an octahedron? Oxygen atoms at each corner and an aluminum atom in the center Aluminum octahedron

44 Tetrahedral sheet Octahedral sheet Assembling the building blocks into sheets

45 1:1 configuration Octahedral sheet Tetrahedral sheet ** * shared oxygen atoms hydroxyl groups Hydrogen atoms 1:1 layer

46 Octahedral sheet Tetrahedral sheet Tetrahedral sheet 2:1 configuration ** * ** * shared oxygen atoms 2:1 layer

47 Hydrogen bonding of 1:1 layers Non-expansive !

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

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

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

51 Spacing of layers can be determined using X-rays Brady and Weil, 2002

52 Properties of some soil colloids Property Size (microns) Surface area (m 2 /g) Net charge (centimol/kg) Smectite0.01 - 1.0650 - 800-80 to -150 Vermiculite0.1 - 0.5700 - 800-100 to -200 Kaolinite0.1 - 5.05 - 30-1 to -15 Fe-oxide< 0.1100 - 300+20 to -5 Humus0.1-1.0variable-100 to -500 Slicate clay minerals Smectite and vermiculite are expansive 2:1 clay minerals Kaolinite is a non-expansive 1:1 clay mineral

53 Impact of parent material and weathering regime on clay formation Degree of weathering Brady and Weil, 2002

54 Clays formed in more intense weathering environments tend to have less charge Brady and Weil, 2002

55 Understanding isomorphic substitution Tetrahedral layers Octahedral layers Exchangeable cations Brady and Weil, 2002

56 pH dependent charge from isomorphic substitution

57 Soils Pure materials Brady and Weil, 2002


59 Fuller’s earth is used to refine and decolorize petroleum products, cottonseed and soy oils, tallow, and other fats and oils. Its high adsorptive power also makes it commercially important in the preparation of animal litter and assorted degreasing agents and sweeping compounds. x1000 tons

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