Soil Degradation: The process of soil losing its fertility and nutrients and becoming biologically dead (reducing in quality and quantity).
Types of Soil Degradation
Soil can be degraded in different ways. The main types of soil degradation are:
Wind and water: Rain or wind blowing away topsoil and causing degradation.
Biological: The loss of humus and or plant/animal life.
Physical: The loss of soil structure or change in permeability.
Chemical: The change in the chemical composition of soil. This could be acidification, salinisation or chemical pollution or loss of nutrients.
The 'Universal Soil Loss Equation' (USLE) predicts the long-term average annual rate of erosion on a field slope based on rainfall patterns, soil type, topography, crop system and management strategies.
A = R x K x LS x C x P
R = Erosivity of Soil: How vulnerable the soil is to being eroded because of rainfall. Intense rainfall or prolonged rainfall causes greater erosion. Rainfall onto bare soil causes greater erosion than onto vegetation.
K = Erodibility: How susceptible the soil is to erosion. Soils with high infiltration rates and strong structure are less vulnerable to erosion.
LS = Length Slope Factor: This is simply the length of the slope and the steepness of the slope.
C = Crop Management: This is the types of crops being grown and the farming practices. Grass and forest provide better protection than many crops. Leaving the land fallow or having prolonged periods between harvests can leave soil vulnerable.
P = Soil Conservation: The type of conservation methods used e.g. contour ploughing, terracing and shelter belts.
The Importance of Soil (Humus and the Nitrogen Cycle)
Soil is a natural body consisting of layers (sometimes called horizons) of minerals that vary in thickness. The layers are different to their source (bedrock) in their shape, size, chemical composition and mineral content. Soil is created through processes of erosion and weathering in situ (in one place) and also by material being transported and deposited from other locations. Most soils also contain humus made from biological matter.
The fertility of soil can depend on the depth of the soil, the mineral content in the soil, the amount of humus in the soil, its drainage, structure and pH (the ideal range is normally between 6.0 and 6.8). Fertile soil is vitally important not only to support the world's ecosystems; rainforest, savanna, etc. but also to allow the production of agricultural crops and the rearing of domesticated animals to meet human needs.
Humus: The fertile layer of soil normally found near the surface. It is made from biological matter (dead plants and animals) which have been broken down and reached a stable state. If you deforest areas and convert to farming, the size and quality of the humus layer can be reduced quickly.
Nitrogen Cycle: The recycling of nitrogen through the ground and atmosphere. Although 78% of our atmosphere is nitrogen, in its gaseous state it is not really useful to plant life so its conversion is extremely important. Plants absorb nitrogen through their roots so it is important that nitrogen is present in soil. Nitrogen in the atmosphere is converted to ammonia in the soil through the process of nitrogen fixation. Bacteria in the soil can then convert the ammonia through the process of nitrification into nitrates which can be absorbed by plants. Nitrogen that already exists in plants and animals is recycled by decomposers (mainly fungi and bacteria). If deforestation takes place then the recycling of nitrogen in the ground stops and the soil will become less fertile.
HUMAN CAUSES OF SOIL DEGRADATION
PHYSICAL CAUSES OF SOIL DEGRADATION
Overgrazing: Allowing to much livestock to graze on a piece of land which means all the vegetation is eaten making the ground susceptible to wind and water erosion. (Lesotho starves in rich SA's shadow - BBC article)
Overcultivation: If you farm land to intensively and don't have fallow (periods of not growing anything) periods then all the nutrients in the soil get used.
Deforestation: Cutting down trees which not only means the land will be receiving less nutrients, but it also means it is more vulnerable to erosion because there is no interception and less stability because the root systems have been removed.
Overpopulation: As the world population continues to grow (now nearly 7 billion) the demand for agricultural products (crops and meat) is increasing causing more land to be deforested, overcultivated and overgrazed.
Fertiliser and Pesticide Use: By using fertilisers and pesticides you can artificially increase yields of crops. However, the process is unnatural and prolonged periods of use can all naturally produced nutrients to be used and local water sources to become polluted reducing the ability of land to cultivate crops and therefore making it vulnerable to chemical degradation as well as wind and water erosion.
HYV and GM Crops: Like with fertilisers and pesticides, it is argued that HYV and GM crops have encouraged overcultivation, diminishing natural nutrients in the soil.
Industrial Pollution: Chemicals, metals and other pollutants leaked from industrial processes can chemical degrade soil making it useless or dangerous for farming. Acid rain caused by pollution can also cause soil degradation.
Unsustainable Water Use (aquifer depletion, unsustainable irrigation): If aquifers or rivers are used unsustainably then areas can become increasingly arid as water resources are used up. A classic example of unsustainable irrigation happened in the Aral Sea (Irrigation and agriculture).
Toyotarisation: This is basically the increased use of 4x4s to travel across grasslands, deserts, etc. damaging topsoil and increasing wind and water erosion.
Conflict: During times of war biological and chemical weapons can be used which degrade the quality of the soil. During the Vietnam war large quantities of agent orange were used to defoliate forests. Much of the land in Vietnam is still degraded because of this 40 years on.
Rising Temperatures: As global temperatures increase it is becoming increasingly hard for vegetation to grow thus reducing vegetation cover and increasing the risk of wind and water erosion.
Falling Rainfall: As the amount of rainfall reduces in some areas like the Sahel, then it is increasingly hard for vegetation to grow again making the ground more vulnerable to wind and water erosion.
Flash floods: Intense periods of rainfall can also cause erosion of topsoil which leads to land degradation.
Wind: If a region is particularly windy then the amount of wind erosion is likely to increase.
Topography: If land is relatively flat then it is much less vulnerable to water erosion, but maybe vulnerable to wind erosion. Alternatively hilly land is vulnerable to water erosion, but maybe protected more from wind erosion.
Main Causes of Soil Degradation In Different Regions
Problems Caused by Soil Degradation
Desertification: The process of fertile land turning into desert. As the soil becomes more degraded and has less nutrients it can not support vegetation and effectively turns to desert.
Dust Storms: As soil become less stable because of the lack of vegetation it become much more vulnerable to wind erosion which can create large scale dust storms. Northern China is suffering from an increased frequency of dust storms as desertification takes place south of the Gobi Desert.
Topsoil Erosion: The top layer of the soil often referred to as the humus layers is very nutrient rich. If the nutrients in this layer begin to reduce then it can support less vegetation and this layer become vulnerable to erosion starting a downward decline in the quality of the soil and reducing its ability to regenerate.
Reduced Crop Yields: As the soil becomes less fertile the amount of crops that it can support will reduce. The falling crop yields can lead to famine and starvation.
Conflict: With increasing soil degradation and reduction in agricultural output and available agricultural land conflict can arise over diminishing resources.
Famine: If the soil become degraded and cops begin to fail or the yields reduce in quantity then famine can happen. Famine is normally caused by a combination of factors, soil degradation, drought and possibly a natural disaster or conflict, so if soil degrades it increases the potential of famine.
Increased Use of Chemicals: Fertiliser use may increase to compensate for the lack of natural nutrients. This increased can worsen the problem as overcultivation continues and pollute water courses.
Possible Solutions to Soil Degradation
Crop Rotation and Fallow Periods: Growing different crops each year, so different nutrients are used and to allow periods of rest (fallow periods) so that soil can regain its fertility.
Terracing and Contour Ploughing: By ploughing with the contours (shape) of the land rather than against it you not only reduce water erosion, but you also reduce the need to irrigate as much. Terraces work on the same principal, they hold water in place rather than encouraging water erosion.
Shelter Belts: Shelter belts (sometimes called wind breaks) are areas of forest or hedge that is left untouched to protect farmland from the affects of water and wind erosion. Shelter belts will often appear around the outside of fields.
Reforestation and Afforestation: By reforesting or afforesting areas you can help return land to its natural state, making it more fertile and stable, thus reducing wind and water erosion and ultimately land degradation.
Fertilisers: Although as we have already learnt fertiliers can cause overcultivation and eventual land degradation, they can also help to add nutrients back into the soil and allow continued cultivation.
Irrigation: It is possible to water areas of land that have become arid to try and the productivity of the soil. However, if water is not used sustainably then irrigation can cause water shortages and land degradation elsewhere.
Grazing Quotas: Placing limits on the number and types of animals that can graze on land, reducing the destruction of vegetation and eventual desertification.
Population Control: The main reason we are putting more pressure on the earth's resources (including soil) is because the world's population has reached 7 billion and is still growing rapidly. If we can control population growth then we can limit the amount of agricultural land we need and the intensity of our farming.
Urban Planning: Controlling growth of cities and using more brownfield sites will reduce the need to deforest areas of land. By keeping forest cover in place, the risk of land degradation should be reduced.
GM Crops: GM stands for genetically modified. GM crops can be engineered to withstand poor soil and water shortages. By growing some types of vegetation you maybe able to add nutrients back to the soil. However, it might it encourage people to farm on unsuitable land causing even further land degradation.
Organic Farming: Organic farming is farming without the use of chemicals. If you farm organically you are less likely to overcultivate and reduce the soil nutrient levels, but you also not going to degrade the soil chemically.
The Sahel is an area of land south of the Sahara Desert, running from Mauritania in the west, through Niger, Burkina Faso, Mali, Chad, Sudan and across to Ethiopian in the west. The Sahel is roughly 5,400km long and covers an area of about 3 million km2. The Sahel receives between 200mm and 600mm of rain annually. The vegetation is mainly savanna (grassland) with some areas of woodland and shrub land. The people of the Sahel are traditional semi-nomadic herders. In recent years the Sahel has been suffering from increasing soil degradation and desertification. The main reasons for increasing soil degradation are:
Population Growth (the population of the region is growing at about 3% a year and doubling every 20 years)
Deforestation (much of it caused by people collecting firewood)
Overgrazing (some of this is caused by loss of land to National Parks and tourist developments and commercial farms)
Colonialism - the creation of borders forced people more into villages making them less nomadic and placing greater pressure on the land.
Rising temperatures (greater evaporation) and reduced rainfall (droughts)
Storms - the rainfall that does take place tends to be in shorter more intense storms that can lead to water erosion.
Desertification has caused many problems in the Sahel including:
Famine
Dust storms
Conflict over diminishing resources
A number of solutions have been suggested to solve the problem of soil degradation and desertification including:
A giant shelter break (the Green Wall) - see article to the right
Population control
Finding alternatives to firewood e.g. solar cookers
Improved farming techniques e.g. reduced grazing numbers
Soil and Change
Soil Degradation: The process of soil losing its fertility and nutrients and becoming biologically dead (reducing in quality and quantity).
Types of Soil Degradation
Soil can be degraded in different ways. The main types of soil degradation are:
Wind and water: Rain or wind blowing away topsoil and causing degradation.
Biological: The loss of humus and or plant/animal life.
Physical: The loss of soil structure or change in permeability.
Chemical: The change in the chemical composition of soil. This could be acidification, salinisation or chemical pollution or loss of nutrients.
The 'Universal Soil Loss Equation' (USLE) predicts the long-term average annual rate of erosion on a field slope based on rainfall patterns, soil type, topography, crop system and management strategies.
A = R x K x LS x C x P
R = Erosivity of Soil: How vulnerable the soil is to being eroded because of rainfall. Intense rainfall or prolonged rainfall causes greater erosion. Rainfall onto bare soil causes greater erosion than onto vegetation.
K = Erodibility: How susceptible the soil is to erosion. Soils with high infiltration rates and strong structure are less vulnerable to erosion.
LS = Length Slope Factor: This is simply the length of the slope and the steepness of the slope.
C = Crop Management: This is the types of crops being grown and the farming practices. Grass and forest provide better protection than many crops. Leaving the land fallow or having prolonged periods between harvests can leave soil vulnerable.
P = Soil Conservation: The type of conservation methods used e.g. contour ploughing, terracing and shelter belts.
The Importance of Soil (Humus and the Nitrogen Cycle)
Soil is a natural body consisting of layers (sometimes called horizons) of minerals that vary in thickness. The layers are different to their source (bedrock) in their shape, size, chemical composition and mineral content. Soil is created through processes of erosion and weathering in situ (in one place) and also by material being transported and deposited from other locations. Most soils also contain humus made from biological matter.
The fertility of soil can depend on the depth of the soil, the mineral content in the soil, the amount of humus in the soil, its drainage, structure and pH (the ideal range is normally between 6.0 and 6.8). Fertile soil is vitally important not only to support the world's ecosystems; rainforest, savanna, etc. but also to allow the production of agricultural crops and the rearing of domesticated animals to meet human needs.
Humus: The fertile layer of soil normally found near the surface. It is made from biological matter (dead plants and animals) which have been broken down and reached a stable state. If you deforest areas and convert to farming, the size and quality of the humus layer can be reduced quickly.
Nitrogen Cycle: The recycling of nitrogen through the ground and atmosphere. Although 78% of our atmosphere is nitrogen, in its gaseous state it is not really useful to plant life so its conversion is extremely important. Plants absorb nitrogen through their roots so it is important that nitrogen is present in soil. Nitrogen in the atmosphere is converted to ammonia in the soil through the process of nitrogen fixation. Bacteria in the soil can then convert the ammonia through the process of nitrification into nitrates which can be absorbed by plants. Nitrogen that already exists in plants and animals is recycled by decomposers (mainly fungi and bacteria). If deforestation takes place then the recycling of nitrogen in the ground stops and the soil will become less fertile.
HUMAN CAUSES OF SOIL DEGRADATION
PHYSICAL CAUSES OF SOIL DEGRADATION
Problems Caused by Soil Degradation
Desertification: The process of fertile land turning into desert. As the soil becomes more degraded and has less nutrients it can not support vegetation and effectively turns to desert.
Dust Storms: As soil become less stable because of the lack of vegetation it become much more vulnerable to wind erosion which can create large scale dust storms. Northern China is suffering from an increased frequency of dust storms as desertification takes place south of the Gobi Desert.
China sandstorm leaves Beijing shrouded in Orange Dust - BBC article
Topsoil Erosion: The top layer of the soil often referred to as the humus layers is very nutrient rich. If the nutrients in this layer begin to reduce then it can support less vegetation and this layer become vulnerable to erosion starting a downward decline in the quality of the soil and reducing its ability to regenerate.
Reduced Crop Yields: As the soil becomes less fertile the amount of crops that it can support will reduce. The falling crop yields can lead to famine and starvation.
Conflict: With increasing soil degradation and reduction in agricultural output and available agricultural land conflict can arise over diminishing resources.
Kenya Drought Worsens Conflict - BBC article
Famine: If the soil become degraded and cops begin to fail or the yields reduce in quantity then famine can happen. Famine is normally caused by a combination of factors, soil degradation, drought and possibly a natural disaster or conflict, so if soil degrades it increases the potential of famine.
Horn of Africa Famine - BBC article
Barren future for Africa's soil - BBC article
Increased Use of Chemicals: Fertiliser use may increase to compensate for the lack of natural nutrients. This increased can worsen the problem as overcultivation continues and pollute water courses.
Possible Solutions to Soil Degradation
Crop Rotation and Fallow Periods: Growing different crops each year, so different nutrients are used and to allow periods of rest (fallow periods) so that soil can regain its fertility.
Terracing and Contour Ploughing: By ploughing with the contours (shape) of the land rather than against it you not only reduce water erosion, but you also reduce the need to irrigate as much. Terraces work on the same principal, they hold water in place rather than encouraging water erosion.
Belgian Farms Tackle Soil Erosion - BBC article
Reforestation and Afforestation: By reforesting or afforesting areas you can help return land to its natural state, making it more fertile and stable, thus reducing wind and water erosion and ultimately land degradation.
Trees boost African crop yields and food security - BBC article
Fertilisers: Although as we have already learnt fertiliers can cause overcultivation and eventual land degradation, they can also help to add nutrients back into the soil and allow continued cultivation.
Irrigation: It is possible to water areas of land that have become arid to try and the productivity of the soil. However, if water is not used sustainably then irrigation can cause water shortages and land degradation elsewhere.
Libya's thirst for fossil water - BBC article
Grazing Quotas: Placing limits on the number and types of animals that can graze on land, reducing the destruction of vegetation and eventual desertification.
Population Control: The main reason we are putting more pressure on the earth's resources (including soil) is because the world's population has reached 7 billion and is still growing rapidly. If we can control population growth then we can limit the amount of agricultural land we need and the intensity of our farming.
Urban Planning: Controlling growth of cities and using more brownfield sites will reduce the need to deforest areas of land. By keeping forest cover in place, the risk of land degradation should be reduced.
GM Crops: GM stands for genetically modified. GM crops can be engineered to withstand poor soil and water shortages. By growing some types of vegetation you maybe able to add nutrients back to the soil. However, it might it encourage people to farm on unsuitable land causing even further land degradation.
Organic Farming: Organic farming is farming without the use of chemicals. If you farm organically you are less likely to overcultivate and reduce the soil nutrient levels, but you also not going to degrade the soil chemically.
China makes gain in battle against desertification - Guradian article
Sahel Case Study
The Sahel is an area of land south of the Sahara Desert, running from Mauritania in the west, through Niger, Burkina Faso, Mali, Chad, Sudan and across to Ethiopian in the west. The Sahel is roughly 5,400km long and covers an area of about 3 million km2. The Sahel receives between 200mm and 600mm of rain annually. The vegetation is mainly savanna (grassland) with some areas of woodland and shrub land. The people of the Sahel are traditional semi-nomadic herders. In recent years the Sahel has been suffering from increasing soil degradation and desertification. The main reasons for increasing soil degradation are:
Desertification has caused many problems in the Sahel including:
A number of solutions have been suggested to solve the problem of soil degradation and desertification including:
Great Green Wall to stop Sahel Desertification - Guardian article
Rays of Hope for Darfur's Refugees - Guardian article
Niger's Complicated Hunger Crisis - BBC article