Activities


Sum Up


HUMAN INTERFERENCE WITH SOILS


l Human activities can destroy natural vegetation and damage soil fertility so that soils are exposed to and eroded by water or wind. l Tropical red soils in the Amazonian rainforests depend on selva vegetation for their fertility. Cattle ranchers and other people deforest vast areas of selva. Deforested soils soon lose their fertility and become exposed to sheet and gully erosion.


l Desert conditions are spreading rapidly in the Sahel region on the south of the Sahara Desert. Overpopulation has resulted in overgrazing, overcropping and vegetation clearance in the Sahel. These activities are major causes of desertification: l Increasing numbers of cattle overgraze land and trample soil. This happens especially where cattle numbers are concentrated near wells and on fenced-off land.


l Overcropping is the excessive cultivation of land. It happens where people grow food crops in unsuitable marginal land. It happened in Niger where people grew groundnuts as a monoculture cash crop without resting or fertilising the soil sufficiently.


l Vegetation is cleared to provide firewood and land for agriculture, especially in areas around large cities. The soil is deprived of the organic matter that vegetation would provide. This deprivation becomes worse if animal dung is also used as fuel.


l All the above activities lead to soil degradation and infertility. Infertile soils become exposed to and are eroded by wind. This results in desertification. People are then forced to migrate into other areas, where the cycle of overpopulation, infertility and desertification continues.


l Soil conservation methods include contour ploughing, terracing and building stone lines on slopes. Windbreaks are used to protect land from wind erosion.


Leaving Cert Higher Level questions: 1. Discuss how human activities can accelerate soil erosion. 2. Examine how overcropping, overgrazing and desertification can affect soils.


Suggested answering method and marking scheme for question 3: Under two main headings, develop three or four different topics or aspects. These headings and topics might be as follows.


Overuse of land: 1 Overgrazing in the Sahel 2 Overcropping in the Sahel


Conservation of land: 1 Stone lines in the Sahel 2 Windbreaks in the Sahel


Each aspect/topic is allocated 20 marks: Identifying (naming) the aspect


See Leaving Cert marking schemes on page 183.


3. Examine two ways in which human activities have impacted on soils.


= 4 marks


Examination: at least 6 SRPs at 2 marks each = 12 marks Overall coherence


= 4 marks


195


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