This document discusses soil erosion, its causes, effects, and methods for prevention. It covers: - Natural and human-caused soil erosion, with the latter including overcropping, overgrazing, and deforestation. - Problems from erosion like loss of topsoil and declining plant productivity. - A case study on erosion and desertification in Africa's Sahel region exacerbated by climate change. - Conservation methods like windbreaks, contour plowing, stubble planting, terraces, and stone walls.

1. Soil Erosion and
Conservation
Page 41 - Geoecology

2. Soil Erosion and Conservation
Exam Brief: Typical Exam Questions
Discuss how human activities can accelerate soil
erosion.(2009)
Examine how overcropping/overgrazing and
desertification can affect soils. (2007)
Examine two ways in which human activities have
impacted on soils. (2010)
Examine the causes of soil erosion and outline
methods used to prevent it. (Sample paper)
See above – the causes of soil erosion are more
important than the solutions – going by past exam
papers.

3. Soil Erosion
Soil is a fragile resource. Most
soil erosion is caused by
natural processes such as
water flowing downhill and by
the wind.

4. Soil Erosion is caused by:
Natural Processes
• Water flowing downhill
• Wind
Human Activities
• Overcropping
• Overgrazing
• Deforestation

5. Problems caused by soil erosion:
1. Loss of valuable topsoil.
2. Burying valuable topsoil.
3. Damage to fields.
4. Plant productivity decline.
5. Desertification.

6. Case Study:
SoilErosionand Desertificationin the Sahel
The Sahel stretches for
5,400km across Africa from the
Atlantic Ocean in the West to
the Red Sea in the East.
It includes countries such as
Mali, Nigeria and Ethiopia.

7. Case Study:
SoilErosionand Desertificationin the Sahel
• Soil erosion (caused by overgrazing, overcropping
and deforestation) is leading to desertification in
the Sahel region of Africa.
• Increased drought in the Sahel region as a result of
climate change is also causing soil erosion and
desertification.

8. Video Clip
• 2009 – BBC News Report about the famine affecting Ethiopia.

9. Overgrazing
• When farmers allow too many animals to graze
an area of land.
• This damages the soil structure and removes
plant cover, allowing the soil to blow away.

10. Overcropping
• When land is continuously farmed, the nutrients
are drained from the soil which destroys soil
structure and makes it less fertile.

11. Deforestation
• Large areas of forest are cut down leaving bare
landscape. Tree and plant roots prevent soil
erosion. When they are removed the soil dries out
due to constant exposure to the sun and is easily
blown or washed away.

12. Climate Change
• Global warming has
caused a rise in the
temperature of the
atmosphere in the
Sahel region.
• As a result the air
can hold more water
vapour and rain is
less likely to occur.
“The rain doesn’t come on
time anymore. After we
plant, the rain stops just as
our crops start to grow.
And it begins to rain after
the crops have already
been ruined.”
- Quote from an Ethiopian
farmer.

13. Methods of Conservation:
Windbreaks / Shelter Belts
Barriers formed by
trees and plants
with many leaves.

14. Methods of Conservation:
Contour / Strip Ploughing
The tractor operator follows
the contours of the hillside.
The furrows thrown up by the
plough (going in different
directions) stop the flow of
water and encourage
percolation in the soil.

15. Methods of Conservation:
Stubble Planting
• The old stubble of harvested
crops is not ploughed back into
the soil (as usually is done).
• Instead the stubble is left in
place in order to reduce wind
and water erosion while the new
crop is growing.

16. Methods of Conservation:
Terraces
• Large steps cut into a hillside.
• This reduces slope length and steepness to
limit the energy of running water and its
ability to carry soil away.

17. Methods of Conservation:
Stone Walls / Bunds
• Low walls placed along the contour of a hill.
• These walls capture water allowing it to filter
into the soil rather than run off downhill.

18. Methods of Conservation:
Reduce ploughing in dry/windy weather
•Ploughing in dry and windy weather
increases the risk of wind erosion.

19. Homework:
Exam Question: 2009 Q 17
‘Discuss how human activities can
accelerate soil erosion’ (80 marks).
Marking Scheme:
And answer Question 8 on pg 50
__________________________________________________________________