Strategies used to manage soil erosion & desertification (Cambridge (CIE) IGCSE Geography) : Revision Note

What are soil erosion & desertification

• Soil erosion is the wearing away of the topsoil by the action of wind or water

• It is a natural process which is made worse by human activities which leave the soil exposed to wind and water

Causes of soil erosion

Deforestation

• Removes the trees reducing interception so the soil is more exposed to the rainfall

• Reduces the amount of roots which reduces infiltration and increases surface runoff

• The bare soil is more exposed to the wind which would have been reduced by tree cover

Overgrazing

• Removes vegetation cover which acts to protect the soil from both wind and water

• More animals trampling the land leads to compaction and increased surface runoff

• This happens more in LEDCs where farmers have less and less land to graze

Over-cultivation

• Land is not left to rest (fallow) between crops and so the fertility of the soil is reduced

Population increase

• More people increase the settlement sizes reducing the areas which can be farmed - increasing over-cultivation and overgrazing

• Increases the demand for food which leads to over-cultivation and overgrazing

Over-abstraction of groundwater

• This leads to the soil moisture content decreasing

• Drier soil is more easily eroded by wind or water

Human-induced climate change

• Changes in climate patterns, increasing floods and increasing droughts all lead to an increase in soil erosion

Salinisation

• Salinisation is also an increasing issue in many semi-arid areas

  • Occurs when high rates of evaporation lead to groundwater being drawn to the surface

  • When the groundwater evaporates salts are left in or on the topsoil

  • These salts make the land toxic to many crops and so the land can no longer be used

Desertification

• Soil erosion may over time lead to desertification

• Desertification is the spread of desert like conditions into semi-arid areas

• It is caused by both natural factors and human activities

• Many of the natural causes may be made worse by human-induced climate change 

Natural causes

• Soil erosion leads to the loss of nutrients

  • As a result, plants cannot establish and grow

• Less predictable rainfall leads to drought and vegetation dying

• Intense rainfall leads to increased surface runoff

• Reduced vegetation means that fewer nutrients are added to the soil

Human causes

• Overgrazing reduces the amount of vegetation so the soil is bare and no nutrients are added to the soil

• Over-cultivation means that the crops take up all the remaining nutrients

• Deforestation decreases:

  • the nutrients added to the soil

  • infiltration

  • interception

  • the number of roots which bind the soil

• Population growth increases the pressure on the land increasing the number of animals and crops

Strategies used to manage soil erosion & desertification

• Halting and reversing soil erosion and desertification means tackling the causes

• There are a variety of political and social responses 

Education

• Education, including:

  • Sustainable farming methods, including agroforestry and crop rotation, help to keep the soil healthy

  • Family planning to reduce population growth

Agroforestry 

• This combines agriculture with forestry, which means some trees remain

• Increases the variety of plants grown which increases biodiversity

Afforestation

• Tree planting, such as the Great Green Wall across the Sahel

Contour Stones and Terraces

• Stones are laid along the contour lines of the land

• These reduce soil erosion and increase nutrients added to the soil

Effectiveness of strategies used to manage soil erosion & desertification

• The strategies outlined have all proved effective in halting and even reversing soil erosion and desertification

Crop rotation

• Improves soil health and structure

• Breaks the cycle of pests and diseases

Agroforestry

• Decreases deforestation because crops are grown alongside the trees

• It provides shade as well as increasing infiltration and interception, which reduces soil erosion

• Provides organic matter from the trees and adds nutrients to the soil

Afforestation

• Afforestation is effective because:

  • The roots of trees help to bind the soil together, reducing soil erosion

  • The canopy offers shade, helping to prevent the soil from drying out and also reducing soil erosion from rainfall landing directly on the soil

  • Nutrients in the soil are replaced by falling leaves and branches

  • The trees increase animal and insect activity, which helps improve soil quality

• Great Green Wall

  • The Great Green Wall project was launched in 2007

  • The project aims to plant an 8 000-kilometre band of trees across 11 Sahel countries

  • By 2024, the Great Green Wall had:

    • Restored 30 million hectares of degraded land

    • Created three million new jobs

  • However, it is only 30% complete and there are only six years left on the project

Contour stones

• These help to reduce soil erosion by:

  • Preventing the soil from being blown or washed away

  • Increasing infiltration of water and reducing overland flow

  • Ensuring that dead organic matter stays in one place and can decompose, adding nutrients to the soil

• In Burkina Faso, Oxfam worked with farmers to improve the traditional stone wall, aiming to increase food production by using bund lines of stones across a slope to stop water and soil from running away

  • This method preserves the topsoil and has improved farming and food production in the village

  • They managed to increase millet, the staple crop in Burkina Faso, production by 50% on average