Lecture 7a: Soil Texture and Surface Tension

3 basic soil particle sizes (in order from smallest to largest)

1. Clay

2. Silt

3. Sand

4 course soil particle sizes (in order from smallest to largest)

1. Gravels

2. Cobbles

3. Stones

4. Boulders

What is the most important property for determining suitability of soil for various uses?

Texture

Texture is considered a basic property because it doesn’t ______

change

Which soil particle is 0.05 to 2 mm?

Sand

True or false. You can see individual sand particles.

True

How does sand feel when it is wet? How does it feel when it’s dry?

Very gritty

How much plant nutrition does sand hold?

Very little

True or false. Sand usually contains more than one mineral.

False. Sand typically contains one mineral - Quartz (SiO2)

What size pore spaces does sand have?

Very large

Does sand have low, medium, or high surface area?

Low

True or false. Sand cannot hold water against the force of gravity.

True

True or false. Sand has very little capacity to hold plant nutrients.

True

Which soil particle is 0.002 to 0.05 mm?

Silt

How does silt feel?

Silky smooth (like flour)

True or false. Silt has a high mineral makeup.

True. And weathering releases plant nutrients.

True or false. Silt is sticky.

False

Silt is susceptible to ________ and piping

erosion

True or false. Silt can’t retain water.

False. Silt CAN retain water.

True or false. Silt can hold nutrients.

True. Silt can hold nutrients.

Which soil particle is less than 0.002 mm?

Clay

Can you see clay with the naked eye?

No, you cannot see a clay particle with the naked eye

Describe clay’s surface area

Very large surface area

Can clay hold water and nutrients?

Yes, clay has a high capacity to hold water and nutrients

Clay particles _____ to each other and other particles

stick

How does clay feel when it is wet? How does it feel when it’s dry?

Clay feels sticky when wet and hard when dry

As particle size decrease, surface area _________

increases

As particle size ________, surface area increases

decreases

As particle size _________, surface area _________

1. decreases

2. increases

Clay has about # times as much surface area as sand

10,000 times

About 6 grams of smectite clay has about as much surface area as what?

A football field

List 5 things that soil surface area (and texture) influence in soil.

1. Water holding capacity

2. Chemical reactions

3. Soil cohesion

4. Cation exchange capacity

5. Ability to support microorganisms

Identify the water holding capacity

1. Low

2. Medium

3. High

Identify the aeration

1. Good

2. Medium

3. Poor

Identify OM (organic matter) decomposition

1. Fast

2. Medium

3. Slow

Identify the water erosion potential

1. High

2. Medium

3. Low* - depends on type of clay

Identify compactibility

1. Low

2. Medium

3. High

Identify sealing ability

1. Poor

2. Poor

3. Good

Identify nutrient supplying ability

1. Poor

2. Medium-high

3. High

Identify pollutant leaching

1. High

2. Medium

3. Low* - depends on type of clay

What are the 2 types of clay?

• 2:1

• 1:1

2:1 clay has # layers of silica bound to # layers of octahedron

2:1

1:1 clay has # layers of silica bound to # layers of octahedron

1:1

Which type of clay is the shirnk/swell clay? 2:1 or 1:1?

2:1

Which type of clay is good @ providing nutrients? 2:1 or 1:1?

2:1

Which type of clay is good for sealing / pond liners? 2:1 or 1:1?

1:1

What is most common 1:1 clay in the area?

Kaolinite

What are the 4 most common 2:1 clays in the area?

1. Illite

2. Chlorite

3. Vermiculite

4. Smectite

Which kind of clay is broken down too far so you don’t know if it was 2:1 or 1:1?

Allophane

What is the cation exchange capacity (meq/100g) of kaolinite?

3-15

What is the cation exchange capacity (meq/100g) of illite?

10-40

What is the cation exchange capacity (meq/100g) of chlorite?

10-40

What is the cation exchange capacity (meq/100g) of vermiculite?

100-150

What is the cation exchange capacity (meq/100g) of smectite?

80-120

What is the cation exchange capacity (meq/100g) of allophane?

30-135

Which type of clay is best cause it hold more nutrients?

a. kaolinite

b. illite

c. chlorite

d. vermiculite

e. smectite

f. allophane

d. vermiculite (it has the highest cation exchange capacity)

Why did the Teton Dam in Idaho fail?

Because they made Zone 1 (the core) out of 2:1 clay instead of 1:1 clay (1:1 has a stronger bond that is better for lining and holding water)