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!!