Soil Structure Flashcards
Why is it important to have gaps in the soil?
They are the location where air, water, roots and soil organisms are found
What does unstructured soil have?
Uniform pore sizes and poor permeability
What do structured soils have?
Variable pore sizes and better permeability
What is soil structure?
The joining together of soil grains into lumps that we call aggregates, PEDS or CLODS
What is an aggregate?
Lumps of soil formed by natural processes
Why is soil structure important?
Good structure is essential to give the soil porosity and permeability
What is porosity?
Volume of soil pores
What is permeability?
Ease with which gases, liquids or roots pass through the soil
What does the ideal soil structure do?
Allows water to penetrate, allows water to drain, allows oxygen in, allows carbon dioxide out, provides room for roots and is stable
What holds soils together?
Clay soil grains, water, humus, lime
What is flocculation?
When lime links the negatively charged sites on clay and holds them together
What is soil structure affected by?
Soil texture, chemical content, organic matter and soil organisms
What else affects soil structure?
Freeze/thaw, wetting/drying, ground cover, compaction and cultivation
Characteristics of granular structure
Less than 5 mm across, slow drainage, good porosity, ideal for root hairs and fibrous roots, easily compacted
Characteristics of sub angular structure
Larger lumps, generally rounded, large pores and fissures, good drainage, moderate root penetration, resist some compaction
Characteristics of prisms columnar structure
Vertical cracks, formed by natural ground movement, ideal sub-soil and below, excellent drainage, good resistance to compaction, only vertical rooting
Characteristics of platy soil structure
Hard surface, horizontal cracks, slow drainage, horizontal roots, often anaerobic, poor seedling emergence, slow repair
