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

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

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) :->.

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

Clay affects many soil properties Brady and Weil, 2002

Clay affects many soil properties Brady and Weil, 2002

Clay affects many soil properties Brady and Weil, 2002

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

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

Special design features for expansive soils Brady and Weil, 2002

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

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

Organic matter content 0-12” (%)

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

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

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

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

Plant available water 0-60” (cm)

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

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

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?

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

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

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 !

Relationship between particle size and mineralogy

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

Clay particles are made of very insoluble materials !

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

Dry soil at the end of an extended dry period

Rain water rapidly infiltrates the surface horizon

Some clay particles disperse in water filled pores

Suspended clay moves downward through macropores to deeper, drier horizons

Capillary action moves water outward into micropores

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

Oriented clay particles coat the walls of dry macropores

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

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

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

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

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

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

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

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

Tetrahedral sheet Octahedral sheet Assembling the building blocks into sheets

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

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

Hydrogen bonding of 1:1 layers Non-expansive !

Expansive 2:1 layers Bentonite Brady and Weil, 2002

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

Different types of phyllosilicate minerals Brady and Weil (2002)

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

Properties of some soil colloids Property Size (microns) Surface area (m 2 /g) Net charge (centimol/kg) Smectite to -150 Vermiculite to -200 Kaolinite to -15 Fe-oxide< to -5 Humus variable-100 to -500 Slicate clay minerals Smectite and vermiculite are expansive 2:1 clay minerals Kaolinite is a non-expansive 1:1 clay mineral

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

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

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

pH dependent charge from isomorphic substitution

Soils Pure materials Brady and Weil, 2002

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