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• Low clay-easy to work & easy to lose
•Intro’ & Overview
• What is SD• Types• Causes• Impact/Effects of SD• Control & Prevention (Solutions)• Comments
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
What is SD (Cont’)
• Slight Degradation• 10% Yield Potential Reduction
• Moderate Degradation• 10-50 % YPR
• Severe Degradation• >50 % YPR
Types or Mechanisms of SD
• Water Erosion• Wind Erosion • Chemical degradation• Physical degradation
Chem. and Phy. Degradation
• Chemical Degradation• Leaching – loss of soil nutrients• Salinization – dry lands –minerals
accumulation on the surface - caliches
• Physical Degradation• Waterlogged
Mechanisms of SD (conti’)
Wind & Water Erosion
• Erosion is the major cause of soil degradation
• Water erosion more severe (vol. & land area)
• Major concern in Southern Africa
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)
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
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
Causes of Soil Degradation
• Deforestation• Exceeds planting by 30:1 in most parts of
Africa
• Overexploitation• Overgrazing• Agric activities (other)• Industrialization
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!!
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
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
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
Setbacks (developing countries)
• $$$• Skilled manpower(lack of)• Tradition & culture
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!!
Top Related