3.1 Phase Distribution and Porosity
Soil is made up of three phases. Name the phases. What is their respective contribution to the soil volume (%)? Why are these percentages not accurate?
These numbers do not account for any type of soil. The phases are not distributed equally in permanently wet groundwater soils or in desert soils. Additionally soils can be subject to short-term changes (swelling/ shrinking, freezing/ thawing, soil management).
3.1 Phase Distribution and Porosity
Define "soil structure".
3.1 Phase Distribution and Porosity
Define "pore structure".
Pore structure is the structure of the cavities, holes, voids, gaps , interstices of the soil.
3.1 Phase Distribution and Porosity
Define "pore".
A pore is an interstice between solid substances. It es the negative matrix of the solid substance (25% air, 25% water). It is idealized as capillaries (small interconnected tubes).
Distinction by...
...size (diameter), formation and fucntion.
Depends on
3.1 Phase Distribution and Porosity
What are "bulk density" and porosity?
Bulk density and porosity are closely linked to the pore volume. They are both very important for the water and air budget of the soil. They depend on four factors: Grain size, organic matter, structure/ texture and management (→ compaction!).
3.1 Phase Distribution and Porosity
Not all pores are the same size. Typically pore size is distributed in coarse pores > 10µm, medium pores 0.2-10µm and fine pores < 0.2µm. What are the characteristics for each pore size? Why does pore size matter for the microbiome?
Coarse pores: > 10 μm
Medium pores: 0.2 - 10 μm
Fine pores: < 0.2 μm
The Size of Microorganisms matters for the pores they live in. The more different pore sizes there are the more divers your soil life is. Most microorganisms live in the big and medium pore sizes.
3.1 Phase Distribution and Porosity
There are two types of pore sizes. Explain.
There are primary pores (in all substrates, grain interstices, obvious with gravel and sand: interstitial or intergranular pores) and secondary pores (formed through soil development, worm and root tubes, shrinkage cracks).
3.1 Important Topic Summarizing Question
Why is porosity so important?
Soil Porosity is important for