Population and climatic pressures have taken their toll on land and resources in Eastern Africa, and the subregion is experiencing some of the most rapid degradation rates in Africa (Henao and Baanante 1999). It has been estimated that 2 million ha of Ethiopia's highlands have been degraded beyond rehabilitation, and an additional 14 million ha severely degraded (EPA/MEDC 1997). The same study estimated that more than 25 per cent of the country is experiencing desertification, and the annual rate of topsoil loss is reported to be 1 900 million tonnes (EPA/MEDC 1997). As farms have been sub-divided over the years, decreasing farm size has led to shorter fallow periods and, in some places, to continuous cropping, in order to sustain productivity levels. Crop residues are rarely ploughed into the soil, and applications of other organic matter have been low, resulting in higher requirements for inorganic fertilizers, with consequent problems of salinization and pollution (FAO 2001c). In the early 1990s, Rwanda and Burundi experienced nutrient depletion rates of more than 100 kg ha/yr of nitrogen, phosphorous and potassium (NPK) (Henao and Baanante 1999). Almost 80 per cent of Kenya's total land area is classified as arid or semi-arid and, in these areas, removal of vegetation cover (through overgrazing and for charcoal production) exposes the soil to wind and water erosion. Soil compaction occurs in areas where there is excessive trampling by animals and, in cultivated areas, soil fertility is declining, as a result of the exhaustion of soils by mono-specific cropping and reduction of fallow periods (FAO/AGL 2000). Colonial land policies have also contributed to degradation through the marginalization of pastoralists, as shown by the example in Box 2f.3. In irrigated areas of Kenya, approximately 50 per cent of the soils are affected by salt, as a result of the poor management of irrigation (FAO/AGL 2000). In Uganda, the estimated proportion of degraded land ranges from 20 per cent to 90 per cent, with soil degradation, resulting from overgrazing and soil compaction, a common feature in the major cattle-rearing areas (FAO/AGL 2000).
|Box 2f.3 Extent and quality of grazing areas|
|Source: Homewood and Rodgers 1991|
In Djibouti, where 85 per cent of the land area is dryland or desert, the remaining 15 per cent of the land has been classified as moderately, severely or extremely vulnerable to desertification. In Eritrea, 42 per cent of the area not already classified as desert is vulnerable. In Ethiopia, this is 26 per cent and, in Kenya, it is 35 per cent (Reich and others 2001). Soil fertility has also declined under cultivation with little organic inputs and short fallow periods. Other causes of land degradation are: inappropriate crop production practices; overgrazing; land fragmentation; deforestation; uncontrolled bushfires; and inefficient mineral exploration techniques. According to Slade and Weitz (1991), the annual cost of soil erosion in Uganda is in the order of US$132-396 million. Soil loss estimates in Ethiopia range from US$15 million (FAO 1986) to US$155 million (Sutcliffe 1993), equivalent to between 1 per cent and 5 per cent of GDP. Cumulative economic losses, as a result of lowered productivity, could reach US$3 000 million for Ethiopia (Bojo 1996).
The impacts of soil degradation include: increased risk of flooding; sedimentation in rivers, lakes and dams; smothering of coastal habitats; and eutrophication. For example, in Uganda, uncontrolled flooding was experienced in 1997-98, as a result of the El Niņo rains, and because of extensive vegetation removal, landslides were experienced (NEMA 1999). In April 1999, thousands of fish deaths were observed in the Albert Nile River, most likely caused by eutrophication, resulting from soil erosion and increased levels of fertilizers in the river. Soil degradation also contributes to rising rural poverty and food insecurity, because productivity is reduced, and subsistence farmers are less and less able to accumulate reserves of grain. Ultimately, rural-to-urban migration and encroachment into gazetted natural reserves occur, as are now extensively experienced in Uganda (NEMA 1999).