Soil Structure

Soil Structure? ‘Arrangement of soil particles, pores

and aggregates within a soil body’

Soil produces aggregates – clumps of soil that stick together

Peds are individual aggregates that form together

Peds - Aggregates

What binds particles together into aggregates?

1. Organic matter, particularly humus2. Plant roots3. Gums secreted by some soil

organisms4. Flocculation caused by the

application of lime.

Ideal structure

1. Crumbs - rounded aggregates 1-5mm

2. Soil that breaks up into crumbs - friable

3. Good soil structure needed to withstand heavy rain and heavy traffic

Types of Soil Structure

1. Sandy soil structure

2. Clayey soil structure

Problems with sandy soil structure

1. Sand - very little structure, can be unstable

2. Grains have no charge and don’t hold onto nutrients well

3. Water can drain too quickly

Improving sandy soil structure

1. Add _________________

2. Dig or c___________ the soil

3. Apply l________ based topdressing

Improving sandy soil structure

1. Add organic matter

2. Dig or cultivate the soil

3. Apply loam based topdressing

Problems with clay structure

1. Can easily compact - small particle size

2. Can be slow draining - little oxygen for roots

3. Limited use of heavy machinery

Improving clay soil structure

1. Add d__________ system

2. Dig or cultivate the soil

3. Avoid heavy t_________ when wet

4. Apply _________ based topdressing

Improving clay soil structure

1. Add drainage system

2. Dig or cultivate the soil

3. Avoid heavy traffic when wet

4. Apply sand based topdressing

Soil structure - compaction Soil particles get

pressed together

Aggregates break down

Less air space for roots to grow into

Causes of compaction

1. _____________________________

2. _____________________________

3. _____________________________

Causes of compaction

1. Foot traffic

2. Heavy machinery

3. Working (preparing) soil when its wet

4. Solution – aeration, manage foot traffic

Activity 2 - write down your definition of these

terms

1. Soil texture ______________________________________________________________

2. Soil structure ______________________________________________________________

Soil texture v Soil structure

1. Soil texture is the composition of the soil in terms of particle size -i.e. % sand, % silt and % clay

2. Soil structure - Arrangement of soil particles, pores and aggregates within a soil body

Self Assessment

1. Define what is meant by soil structure

2. State how you would improve sand soil structure

3. State how you would improve clayey soil structure