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Soil Degradation and Loss of Nutrients in Soils in Africa

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Soil Degradation and Loss of Nutrients in Soils in Africa-Lesego N. Olefhile 05.01.2002 General Continent has been occupied by humans much longer than other ... – PowerPoint PPT presentation

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Title: Soil Degradation and Loss of Nutrients in Soils in Africa


1
Soil Degradation and Loss of Nutrients in Soils
in Africa
  • -Lesego N. Olefhile
  • 05.01.2002

2
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3
General
  • Continent has been occupied by humans much longer
    than other continents
  • Human activity and its repercussions
  • Bedrock mainly granite and gneiss
  • Low fertility
  • Rocks oldest in the world
  • Low clay-easy to work easy to lose

4
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5
Intro Overview
  • What is SD
  • Types
  • Causes
  • Impact/Effects of SD
  • Control Prevention (Solutions)
  • Comments

6
What is Soil Degradation
  • Soil Degradation is a Reduction in the Soils
    Ability to Produce
  • Qualitatively quantitatively
  • Results in decreased food production
  • Declining yields
  • Increasing levels of poverty

7
What is SD (Cont)
  • Slight Degradation
  • 10 Yield Potential Reduction
  • Moderate Degradation
  • 10-50 YPR
  • Severe Degradation
  • gt50 YPR

8
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9
Types or Mechanisms of SD
  • Water Erosion
  • Wind Erosion
  • Chemical degradation
  • Physical degradation

10
Chem. and Phy. Degradation
  • Chemical Degradation
  • Leaching loss of soil nutrients
  • Salinization dry lands minerals accumulation
    on the surface - caliches
  • Physical Degradation
  • Waterlogged

11
Mechanisms of SD (conti)

12
Wind Water Erosion
  • Erosion is the major cause of soil degradation
  • Water erosion more severe (vol. land area)
  • Major concern in Southern Africa

13
Causes of SE
  • Monoculture
  • Common practice in Africa
  • Deforestation -Fuel
  • -Building materials
  • 37 million ha of forest disappearing each yr
    (FAO, 1986)
  • Marginal lands farming- pop. Increase
  • Hillsides
  • Malawi 12 slope land cultivated (FAO)

14
Causes of SE (cont)
  • Row cropping
  • Crop removal
  • Overgrazing
  • Accounts for about half of the soil
    degradation in Africa-(FAO)
  • Tilling or plowing
  • All lead to Soil Degradation

15
SE in Africa
  • Most erosion occurs in
  • Liberia, Guinea,Ghana, Nigeria, Zaire,Ethiopia,
    Senegal, Niger, The Sudan,Somalia and Sierra
    Leone
  • -FAO
  • Ethiopia 1,900 T of soil lost annually from the
    highlands -UN

16
Causes of Soil Degradation
  • Deforestation
  • Exceeds planting by 301 in most parts of Africa
  • Overexploitation
  • Overgrazing
  • Agric activities (other)
  • Industrialization

17
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18
SD vs desertification
  • Desertification degradation of land in dry areas
    of the world due to misuse or overuse
  • Advanced Soil Degradation
  • Destroys soils capacity to support livestock or
    grow crops
  • 24 million tones of top soil every yr over the
    world
  • Costs Africa about US9 billion per year (UN)
  • Not the spread of existing deserts!!

19
Loss of nutrients
  • Loss of top soil
  • Loss of soil minerals
  • Many areas in Africa losing about 50 tones of
    soil/ha/yr
  • Equivalent to loss of 20,2 41 billion tones of
    N,P K respectively per yr.
  • -UNEP

20
Impact of Soil Degradation
  • Decline in soil fertility
  • Decline in biomass produced
  • Decrease in food production
  • Starvation Poverty
  • By 2025 Africa ll feed only 40 of its pop
    (FAO)
  • gt ¼ of Africa becoming useless for cultivation
    due to SD.

  • -UNEP

21
Solutions
  • Implementation of Govt. Policies
  • -Soil erosion prevention schemes
  • Precision Ag???
  • Advanced farming methods
  • - conservation tillage
  • GLASOD - Global Assessment of Soil Degradation
    estimates extent severity of SD.-sponsored by
    UNEP ISRIC

22
Setbacks (developing countries)
  • Skilled manpower(lack of)
  • Tradition culture

23
Comments /or Questions
  • Is there a direct link between erosion and soil
    degradation???
  • Can degraded soils be restored to full function?
  • Lightly and mod. Degraded soils NOT severely
    Degraded soils!!
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