Essay - Human Activities Affecting Soils

* I have studied Desertification in the Sahel Region in Africa *

The Sahel is a vast region which stretches for over 6000km from west to east Africa, including parts of Nigeria, Chad and Sudan. It lies to the south of the Sahara Desert but to the north of the Savannah grasslands and equatorial rainforests. It receives rain only during a short season from late June to September. It is covered by some grasslands and supports nomadic, pastoral-based societies. Research published between 1975 & 1996 proved that the Sahara Desert is advancing southwards into the Sahel at a rate of 5km to 10km per year. This process, the sprawling of desert into new areas, is known as desertification. It means that land that was once productive quickly turns unproductive and, therefore, useless.

Desertification has two main causes:

Overgrazing - This occurs when farmers allow too many animals to graze one particular area of land for a prolonged period, particularly close to water sources. The animals damage the soil structure, remove vegetation cover and loosen the topsoil. It can then be easily blown away during the dry season or washed away during the wet season. In the Sahel, nomadic tribes herd large numbers of livestock, as owning animals is a symbol of wealth. The population of the Sahel has grown in recent years meaning that the number of animals has increased too. This overgrazing has led to the loss of vegetation cover with large herds trampling the soil with their hooves and eating any grasses. As a result, the soil structure has been damaged beyond repair. Vegetation has been unable to re-establish itself. This lack of vegetation means that there is nothing left to intercept raindrops; therefore, heavy rain falls directly onto the soil, loosening it. This leads to sheet erosion (where the whole top layer is washed away evenly in one go). Alternatively, in dry weather, strong winds can lift the upper layer and take it with them. Such an absence of vegetation also means that there is no plant litter available for the development of humus and, so, it is unlikely that it will be able to support plant life again in the future.

Overcropping/Overcultivation - This occurs when the soil is continuously cultivated and people use the land, year after year, without practising crop rotation, allowing rest periods or properly fertilising it. This practice drains nutrients from the soil and damages the soil structure. The soil quickly becomes dry, dusty and susceptible to weathering and erosion. Due to the growing population in the Sahel, people are being forced to attempt to grow more food in already weakened soils in order to survive. The land is being overcropped/overcultivated and is not allowed any rest time between crops. It is not fertilised properly either as they cannot afford to do so. Therefore, the land on the margins of the desert is continuously in use. It cannot be left fallow to regain its nutrients as people would go hungry and that is not a viable option. The other reason for overcropping/overcultivation in this area is the growing of cash crops (e.g. cotton, nuts, etc) in huge plantations. The countries of the Sahel availed of cheap loans in the 1960s but now have great trouble in meeting the repayments. In order to qualify for debt relief, they have to sell cash crops on the international market. However, the price of these cash crops has fallen in recent years putting even further strain on the soil as they now need to produce even more to break even. This monoculture (the growth of the same crop every year on the same piece of land) is destroying their already exhausted soils. Ideally, the soil in such areas should be left fallow for six years after every three years intense production; however this is not feasible. Deep ploughing also destroys the soil structure and loosens the topsoil. As a result, vegetation is refusing to grow, meaning that the soil is left without any protective cover and, therefore, is easily eroded by wind and rain.

Deforestation - This is the large scale clearing away of vast areas of woodland and forest. When this happens, the soil is exposed to both wind and rain and so erosion takes place. Again, because of their ever-increasing population in the Sahel, more and more trees are having to be cut down to provide wood for fires and building materials and to make way for subsistence farming (just to survive). The removal of its nutrient source and the destruction of soil structure means that the land is useless for farming. As a result, the land is abandoned, leaving the soil to be even further eroded by the wind and rain. Again, the lack of vegetation means that there is nothing left to intercept the raindrops; therefore, heavy rain falls directly onto the soil, loosening it. The removal of roots also means that there is nothing left to bind the soil together anymore.