Soil Structure

1. Soil Structure

2. 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

3. Peds - Aggregates

4. What binds particles together into aggregates? • Organic matter, particularly humus • Plant roots • Gums secreted by some soil organisms • Flocculation caused by the application of lime.

5. Ideal structure • Crumbs - rounded aggregates 1-5mm • Soil that breaks up into crumbs - friable • Good soil structure needed to withstand heavy rain and heavy traffic

6. Types of Soil Structure • Sandy soil structure • Clayey soil structure

7. Problems with sandy soil structure • Sand - very little structure, can be unstable • Grains have no charge and don’t hold onto nutrients well • Water can drain too quickly

8. Improving sandy soil structure • Add _________________ • Dig or c___________ the soil • Apply l________ based topdressing

9. Improving sandy soil structure • Add organic matter • Dig or cultivate the soil • Apply loam based topdressing

10. Problems with clay structure • Can easily compact - small particle size • Can be slow draining - little oxygen for roots • Limited use of heavy machinery

11. Improving clay soil structure • Add d__________ system • Dig or cultivate the soil • Avoid heavy t_________ when wet • Apply _________ based topdressing

12. Improving clay soil structure • Add drainage system • Dig or cultivate the soil • Avoid heavy traffic when wet • Apply sand based topdressing

13. Soil structure - compaction • Soil particles get pressed together • Aggregates break down • Less air space for roots to grow into

14. Causes of compaction • _____________________________ • _____________________________ • _____________________________

15. Causes of compaction • Foot traffic • Heavy machinery • Working (preparing) soil when its wet • Solution – aeration, manage foot traffic

16. Activity 2 - write down your definition of these terms • Soil texture ______________________________________________________________ • Soil structure ______________________________________________________________

17. Soil texture v Soil structure • Soil texture is the composition of the soil in terms of particle size -i.e. % sand, % silt and % clay • Soil structure - Arrangement of soil particles, pores and aggregates within a soil body

18. Self Assessment • Define what is meant by soil structure • State how you would improve sand soil structure • State how you would improve clayey soil structure