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Soil Degradation and Loss of Nutrients in Soils in Africa

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 continents Human activity and it’s repercussions Bedrock mainly granite and gneiss Low fertility Rocks oldest in the world

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Soil Degradation and Loss of Nutrients in Soils in Africa

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

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

  3. Intro’ & Overview • What is SD • Types • Causes • Impact/Effects of SD • Control & Prevention (Solutions) • Comments

  4. 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

  5. What is SD (Cont’) • Slight Degradation • 10% Yield Potential Reduction • Moderate Degradation • 10-50 % YPR • Severe Degradation • >50 % YPR

  6. Types or Mechanisms of SD • Water Erosion • Wind Erosion • Chemical degradation • Physical degradation

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

  8. Mechanisms of SD (conti’)

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

  10. 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) Causes of SE

  11. 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

  12. 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

  13. Causes of Soil Degradation • Deforestation • Exceeds planting by 30:1 in most parts of Africa • Overexploitation • Overgrazing • Agric activities (other) • Industrialization

  14. SD vs desertification • Desertification= degradation of land in dry areas of the world due to misuse or overuse • Advanced Soil Degradation • Destroys soil’s 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!!

  15. 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

  16. 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 it’s pop (FAO) • > ¼ of Africa becoming useless for cultivation due to SD. • -UNEP

  17. 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

  18. Setbacks (developing countries) • $$$ • Skilled manpower(lack of) • Tradition & culture

  19. 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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