1. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
Soil
More than just dirt

2. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
Soils are:
• The part of the lithosphere where life
processes and soil forming processes both
take place.

3. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
What is soil made from?
Soils can be thought of as being made up of four main
components.
• Mineral particles mainly from the underlying rock
• Organic remains that have come from the plants and animals
• Water within spaces between soil grains
• Air within the soils grains

4. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
Soil profile

5. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
The soil profile can be divided into HORIZONS
O - newly added organic material such as leaf litter
A - where in many soils humus builds up. Humus forms from partially
decomposed organic matter and often mixed with fine mineral
particles
B - the layer where soluble minerals and organic matter tends to be
deposited from the layer above by leaching. In particular clay and iron
salts can be deposited in this horizon
C - This layer is mainly unaltered rock from which the soil forms

6. Topic 3: Human population, carrying
capacity and resource use
3.4: Soil System
How do soils form?
• S = ƒ cl. o. r. p. t. . . .
• S = soil, cl = climate, o = organisms, r = relief (land
shape, topography), p = parent material, t = time
(Jenny: 1941)