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Soil Degradation and Loss ofNutrients in Soils in Africa

-Lesego N. Olefhile

05.01.2002

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General

Continent has been occupied by humansmuch 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

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What is Soil Degradation

Soil Degradation is a Reduction in the SoilsAbility to Produce

Qualitatively & quantitatively Results in decreased food production

Declining yields

Increasing levels of poverty

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What is SD (Cont)

Slight Degradation

10% Yield Potential Reduction

Moderate Degradation 10-50 % YPR

Severe Degradation

>50 % YPR

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Types or Mechanisms of SD

Water Erosion

Wind Erosion

Chemical degradation

Physical degradation

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Chem. and Phy. Degradation

Chemical Degradation

Leachingloss of soil nutrients

Salinizationdry landsmineralsaccumulation on the surface - caliches

Physical Degradation

Waterlogged

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Wind & Water Erosion

Erosion is the major cause of soildegradation

Water erosion more severe (vol. & landarea)

Major concern in Southern Africa

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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)

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Causes of SE (cont)

Row cropping

Crop removal

Overgrazing

Accounts for about half of the soildegradation in Africa-(FAO)

Tilling or plowing All lead to Soil Degradation

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SE in Africa

Most erosion occurs in

Liberia, Guinea,Ghana, Nigeria,

Zaire,Ethiopia, Senegal, Niger, TheSudan,Somalia and Sierra Leone

-FAO

Ethiopia1,900 T of soil lost annually fromthe highlands -UN

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Causes of Soil Degradation

Deforestation

Exceeds planting by 30:1 in most parts of

Africa Overexploitation

Overgrazing

Agric activities (other) Industrialization

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SD vs desertification

Desertification= degradation of land in dry areasof 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 US$9 billion per year (UN) Not the spread of existing deserts!!

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Loss of nutrients

Loss of top soil Loss of soil minerals

Many areas in Africa losing about 50 tonesof soil/ha/yr Equivalent to loss of 20,2 & 41 billion tones of

N,P & K respectively per yr.

-UNEP

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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)

> of Africa becoming useless for cultivationdue to SD.

-UNEP

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Solutions

Implementation of Govt. Policies -Soil erosion prevention schemes

Precision Ag??? Advanced farming methods

- conservation tillage

GLASOD - Global Assessment of SoilDegradationestimates extent & severityof SD.-sponsored by UNEP & ISRIC

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Setbacks (developing countries)

$$$

Skilled manpower(lack of)

Tradition & culture

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Comments &/or Questions

Is there a direct link between erosion andsoil degradation???

Can degraded soils be restored to fullfunction?

Lightly and mod. Degraded soils NOT severelyDegraded soils!!