1. SOIL - OUR BREAD BASKET

2. INDEX What is soil? What is the importance of soil?
What are the different layers of soil?
How does soil form?
What is calcification and salinisation?
What factors influence soil formation?
What is the human impact on soil?

3. The ingredients of soil

4. uppermost layer of loose inorganic, weathered rock …
Soil is the …
uppermost layer of loose inorganic, weathered rock …
mixed with organic matter, air and water.
Varies in depth from few cm to 100’s of metres.

5. Which of these soils are best for agriculture? Explain
Loamy Soils
Sandy Soils
Clay Soils

6. Soil is essential because it …
provides nutrients and water to plants.
anchors plants.
provides a habitat for animals and micro-organisms.
is used to grow crops.

7. Soil Profile
Soil has different layers or horizons:
O Horizon

8. What are the characteristics of each layer ?
Humus: Fallen leaves, organic debris + partially decayed organic matter.
Topsoil: Rich in humus, porous, partially decomposed organic matter + inorganic minerals. Water trickles through and carries nutrients to layer B. (leaching)
O Horizon
A or eluvial Horizon
Topsoil
True soil (solum)
B or illuvial Horizon
Subsoil: accumulation of nutrients, clay, minerals from A.
Subsoil
Parent material: Partially broken down bedrock, forms soil.
C Horizon
Regolith
Bedrock: impenetrable layer of parent rock, solid.
R Horizon
Bedrock

9. Explain how the following processes lead to soil formation?
Soil forming is continuous as a result of processes such as:
Weathering
Humus formation
Leaching/ Uitloging
Eluviation/ Eluviasie
illuviation/ illuviasie

10. Weathering weakens and breaks down the parent rock.
Soil organism decompose organic material to form humus
Eluviation is the movement of fine particles to the B horizon
Leaching by water carries dissolved minerals and nutrients downwards through the soil
Illuviation is the accumulation of dissolved minerals, particles and nutrients in the B horizon

11. What is calcification and salination?
Dry regions have rapid evaporation rates
Irrigation causes certain salts like sodium, magnesium ….
and calcium to be deposited in upper layers of soil.
This reduces infiltration …
and nutrients become inaccessible to plants.
Soil gets a hard crust (calcification)
White, salty, toxic crust (salination)

12. Soil Forming Factors
Soil formation is influenced by five soil forming factors:
Parent material / Moedermateriaal
Relief or topography / Reliëf of topografie
Time or age of soil
Climate / Klimaat
Actions of organisms
These factors are all interdependent.
Passive factors
Active factors

13. How does parent material influence soil formation?
Bedrock from which the soil weathers …
influences colour, mineral content, texture.
Granite: light coloured soil
Rocks with iron: reddish soil
Sandstone: has lots of silicon due to quartz
Sandstone: will have a sandy, well-drained texture.

14. How does climate affect soil formation?
Amount of rain determines the rate of ….
chemical and biological processes...
and leaching.
Rainfall
Determines rate of decomposition…
and weathering.
In warm tropical areas:
organic matter is destroyed rapidly.
little humus remains…
and soil is deep, but infertile
In dry, hot/cold regions:
decomposition is slower.
poor shallow soils result.
Temperature
Determines rate of evaporation….
and removal of topsoil.
Wind

15. Actions of organisms: Age of Soil: Topography:
Bacteria + fungi decompose matter into humus.
fast in tropical regions.
too slow in cold regions.
Humus forms best in temperate grasslands.
Earthworms and termites aerate + mix soil.
Age of Soil:
Soil forms slowly.
Mature soils have well-developed horizons e.g. old landscapes
Immature soils have fewer horizons + shallower e.g. river + glacial deposits.
Topography:
Steep slopes have shallow soils i.e. carried downwards
Gentle slopes have deep, well-drained soils.
Hollows e.g. marshes have poorly-drained, thick, dark soils.

16. Topography

17. Human Impact on Soil Quality
Soil forms slowly.
1cm in 400 yrs
productive soil takes yrs
Soil is non-renewable
destroyed faster than it’s being replaced
Soil Degradation:
decline in soil quality to sustain vegetation
Soil Erosion:
The removal of topsoil at such a fast rate that it can no longer support its natural vegetation.

18. Rate of soil erosion in South Africa

19. Click on A and then B for further information
Causes of Soil Erosion
Overgrazing
Deforestation
Click on A and then B for further information
Parallel ploughing:
Leads to more runoff of rainwater that form gullies and later dongas.

20. Deforestation Deforestation occurs due to population pressure when:
Trees are removed for firewood
Vegetation is cleared for agriculture
and for development of settlements
Soil becomes exposed.
Wind and water removes fertile topsoil at a faster rate.
More runoff occurs and dongas form.
Vegetation binds soil and retains water so less surface runoff occurs.
Forest cleared for cultivation

21. Overgrazing
When too many cattle graze on land that exceeds carrying capacity of soil.
Vegetation is damaged and soil is trampled.
Vegetation dies and soil is left barren and exposed to soil erosion.
Avoid overgrazing by:
Reducing the number of cattle
Rotational grazing

23. Results of Soil Erosion
The loss of topsoil.
This leads to lower productivity.
Run off increases as a result of soil erosion.
Dams silt up (silting of dams) .
Conservation measures are costly.
Can lead to severe desertification

24. Preventing soil erosion

25. Proper road and rail construction Consider carrying capacity
Rotational grazing
Strip cultivation
Add humus and fertilizer
Proper road and rail construction
Consider carrying capacity

26. DESERTIFICATION What is desertification?
process by which once productive farmland is converted to a wasteland or desert.
Soil cannot further support any vegetation.

27. The Process of Desertification
Sustainable community
Higher demand for food
Over-cultivation
Overgrazing
Deforestation
Cultivation = adequate
fallow time for
soil to recover
No population
pressure on land =
balance with carrying
capacity of land
Improved medical services =
Higher birth rate

28. The Process of Desertification
Dongas form =
Water erosion