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Soil Structure
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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
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Peds - Aggregates
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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.
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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
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Types of Soil Structure
1. Sandy soil structure
2. Clayey soil structure
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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
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Improving sandy soil structure
1. Add _________________
2. Dig or c___________ the soil
3. Apply l________ based topdressing
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Improving sandy soil structure
1. Add organic matter
2. Dig or cultivate the soil
3. Apply loam based topdressing
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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
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Improving clay soil structure
1. Add d__________ system
2. Dig or cultivate the soil
3. Avoid heavy t_________ when wet
4. Apply _________ based topdressing
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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
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Soil structure - compaction Soil particles get
pressed together
Aggregates break down
Less air space for roots to grow into
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Causes of compaction
1. _____________________________
2. _____________________________
3. _____________________________
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Causes of compaction
1. Foot traffic
2. Heavy machinery
3. Working (preparing) soil when its wet
4. Solution – aeration, manage foot traffic
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Activity 2 - write down your definition of these
terms
1. Soil texture ______________________________________________________________
2. Soil structure ______________________________________________________________
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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
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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