Lecture 7a: Soil Structure

Sand, silt, and clay particles are rarely ________ of each other.

independent

Sand, silt, and clay particles are rarely independent of each other. They form _________.

aggregates

Which type of soil aggregates are comprised of smaller particles (2-250μm)?

Microaggregates

Which type of soil aggregates are relatively large (0.25-5mm) and comprised of smaller microaggregates?

Macroaggregates

Which type of soil aggregates are large-scale structures that are evident when observing soil profile?

Peds

Soil aggregation involves not only mineral particles, but also ______ _______ and ______ ________.

1. Organic matter

2. Living organisms

Identify 1 - 4

1. Macroaggregate

2. Microaggregate

3. Submicroaggregate

4. Primary particles

What is the glue that holds aggregates together?

OM

Which retains its structure better after getting wet? Soil with more or less organic matter?

The soil with more organic matter will retain more structure after getting wet because the OM is the glue that holds the structure together.

Soil structure is important for ______ & _______ movement

water & air

6 main soil macro structures

1. Single-grained

2. Massive

3. Granular

4. Blocky

5. Prismlike

6. Platy

Which soil structure has rapid drainage?

Single-grained

Identify the soil structure

Single-grained

Single-grained soil is mostly _____

quartz

True or false. Single-grained soil has aggregation.

False. There is no aggregation

Does single-grained soil have low, medium, or high organic matter?

Low

Which soil structure is large, cohesive mass of material?

Massive

Identify the soil structure

Massive

Identify the soil structure

Massive

Massive soil structure is observed in certain ____ sediments

clay

Does massive soil have low, medium, or high porosity / permeability?

Low which is bad for plant roots

Identify the structure

Granular

Identify the structure

Granular

Identify the structure

Granular

Which structure is spherical aggregates?

Granular

Granular structure are _____ packed together

loosely

Granular structure is typically ____ in organic matter

high

Granular soil is ___ porous

very

Granular structure is often observed in which master horizon?

A

Which soil structure is susceptible to rapid changes

True

Does massive drain slow or fast?

Slow

Which structure is most easily destroyed?

Granular

Granular structure can easily turn to single grain via _______ and to massive via _________

1. tillage

2. compaction

Blocky is common in which master horizon?

B

Which structure has irregular, cubelike peds?

Blocky

Identify the structure

Blocky

Identify the structure

Angular blocky

Identify the structure

Angular blocky

Identify the structure

Subangular blocky

Identify the structure

Subangular blocky

What are the 2 types of blocky?

1. Angular

2. Subangular

Which type of blocky has sharp edges?

Angular

Which type of blocky has more edges due to water?

Subangular

Identify the structure

Prismlike

Which structure is vertically oriented pillar like peds?

Prismlike

Some prismlike can be very large, even greater than #mm in diameter

150mm

Which structure is associated with swelling clays?

Prismlike

Which horizon is prismlike most often found in?

B

Prismlike is common in which type of region?

Arid

2 types of prismlike

1. columnar (rounded top)

2. prismatic (flat, angular tops)

What is the difference between culumnar and prismatic?

Columnar has rounded tops. Prismatic has flat, angular tops.

Identify the structure

Columnar

Identify the structure

Columnar

Identify the structure

Prismatic

Identify the structure

Prismatic

Identify the structure

Platy

Identify the structure

aty

Which structure is thin horizontal sheet peds?

Platy

Platy is caused by soil forming process or __________ parent material

alluviam

Compaction may create which strucutres?

Massive or platy

Does platy have low, medium, or high porosity?

Lower

Which two structures have slow drainage?

1. Massive

2. Platy

Which two structures have moderate(ly fast) drainage?

1. Blocky

2. Prismatic

Which tso structures have rapid drainage?

1. Single-grain

2. Granular