Discuss how human activities can accelerate soil erosion.
Soil erosion is when soil particles in the land get transported by gravity, water or wind. The human processes that accelerate soil erosion are overgrazing, over-cropping and desertification.
Overgrazing
Overgrazing occurs when farmers stock too many animals such as sheep, cattle or goats on their land. This damages the soil surface and increases the rate of soil erosion. Animals eat the vegetation cover and their hooves dig into the soil in wet areas or compact it into a hard surface in dry regions. This prevents grass growth and prevents water from percolating into the soil. Dry soils are eroded by the wind very easily. Once the soil has been trampled on and stripped of plants, its structure is damaged and its ability to hold water and nutrients is reduced. Soil structure is important because plant roots and water are found in the spaces between the soil peds. Peds are the small grains which are held together by humus and water. Peds have different shapes. Rounded peds give the soil a crumb structure. A crumb structure is best for soil aeration, water content and fertility. Overgrazing can change the structure to a platy structure or destroy the structure completely. As a result it can be easily eroded by wind and rain and pasture growth is also reduced. Too many animals on the land will eat all the plants and strip the soil of its protective vegetation cover. Plants, roots and branches protect soil from wind and rain. Soils that are exposed become drier and are easily blown or washed away. This situation has happened in many places around the world such as the Sahel region of Africa where population growth has led to an increase in the number of cattle and goats grazing on already dry land. It also occurred in Co. Mayo in Ireland during the 1990's when EU farm subsidies encouraged farmers to overstock their land with too many sheep. The fragile boglands of West Mayo were severely damaged.
Over-cropping
Over-cropping occurs when the land is under continuous cultivation and is not allowed to lie fallow in between crops. The effect of over-cropping on soils is to reduce its water content and fertility. Infertile soils are more easily eroded by wins and rain. As nutrients are removed its structure is damaged as well. Over-cropped soils become dry and very dusty because the humus content has been reduced. Humus is important for improving the texture and structure of soil and for keeping it moist. In the Sahel region of Africa, over-cropping and overgrazing often occur together as a result of population increase. More people on the land leads to greater numbers of farmers who keep animals and grow crops. There is also less land to go around so whatever amount of land is available is under stress to produce food for the increasing population. Intensive cultivation of land in the soya plantations of South America can also lead to over-cropping. Here the soil is fertilized but the application of chemical fertilizers does not benefit the land as much as applying manure from animal waste. Therefore, over time the soil structure is damaged as it is over-cropped. The effect of over-cropping can be reduced by the addition of organic matter (cattle dung) to the soil and through immigration.
Desertification
Desertification is the spread of desert conditions into new ares. Desertified soils are dry , dusty and lack humus. Their fertility is reduced and they are affected by soil erosion. Africa is the continent most at risk from desertification, although Southern Europe, especially Southern Spain, is also at risk. Desertification often occurs as a result of a combination of drought, over-cropping, overgrazing and deforestation. High population growth in countries such as Sudan contributes to desertification due to the increases demand for food and fuel. Drought conditions increases the chance of desertification occurring when the soil is already stressed by over-cropping and overgrazing. In Sahelian countries such as Chad and Niger, cotton and cashew nuts are grown as cash crops on huge plantations as part of economic reforms in return for debt relief. People are removed form their land to make way for the plantations and must make a living on poor land at the edge of the plantations. The land is overgrazes and over-cropped and trees are cut down for fuel and building materials. Because so many trees have been cut down, cattle dung is used for fuel instead. This further deprives the soil of valuable nutrients, leading to increases desertification in the region during drought. The introduction of solar cookers in the Sahel could reduce the need for timber as a fuel. Trees are then planted which can help slow desertification in the region.
Everywhere in the world where people change a natural ecosystem into agriculture, the land degrades. The visible part is erosion, when soil particles leave the land, transported by gravity, water or wind.
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