Embedded Files
What you should know by the end of this lesson:
What you should know by the end of this lesson:
Soil profiles and their different aspects
What is a soil profile?
What is a soil profile?
Soils can be examined by looking at a vertical section through the soil from topsoil (most recently deposited) to parent material (weathered bedrock).
Soils develop a series of distinct layers called horizons. These horizons are identifiable by colour and texture and have different material compositions and mineral content.
By examining these horizons, it is possible to work out the type of soil.
Soil Layers and Key Terms
Soil Layers and Key Terms
Digital Workbook and Paper Jotter
Take a Blank page in your jotter
Copy in the Generic soil profile to the middle of your page
Annotate it with the information about each later so you can use it for reference when creating your soil profiles
O horizon - Humus
The O horizon is the layer of humus that is found on the surface. It forms from the leaves/ pine needles/pine cones that fall from the vegetation on the surface.
Present at the surface.
Essentially decaying vegetation.
Consists of litter (leaves etc.), fermentation (organic matter decomposes) and humus (decomposed vegetation, animals and bacteria).
A horizon (Topsoil)
The A horizon and B horizon are where nutrients from the humus and the minerals from the C horizon are mixed.
Mixture of organic and inorganic material.
Wet conditions: water flows down through the soil, removing nutrients and minerals from the humus. This is known as leaching. It involves:
Eluviation – washing out of A horizon.
Illuviation – washing into B horizon.
B horizon (Subsoil)
Less organic matter.
Coarser in texture, reflecting the importance of weathering.
Soluble soil material containing nutrients may be leached out of A into B.
C horizon (Parent Rock/Weathered bedrock)
Dry conditions: evaporation is greater than precipitation, and as a result water moves up through the soil bringing minerals up from the C horizon. This is known as capillary action.
Large particles sit on underlying bedrock.
Formed by the decay of the parent rock with minerals being released.
All Horizons
Plant roots create passages through which material from the humus can percolate into the A and B horizons.
Animals - worms and moles can assist in taking materials from humus and depositing it further down. They can also help to mix the soil.
World soil distribution
World soil distribution
Climate plays an important role in soil formation, soils differ widely from one major climatic zone to another. The importance of climate for soil formation was recognized by early soil scientists, and the concept of zonality was developed. This concept distinguished zonal soils (soils corresponding to the major climatic belts of the Earth), azonal soils (soils not yet in equilibrium with the present-day climatical conditions) and intrazonal soils (soils that are strongly subject to local conditions other than climate).
Well done you have finished lesson 2 of Biosphere
Well done you have finished lesson 2 of Biosphere
Return to the topic launch page and attempt the lesson quiz
Return to the topic launch page and attempt the lesson quiz
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