Tuesday, February 13, 2007

Soil Erosion in West Africa

Given our erosion problems here in the Piedmont of the southeastern United States, I am not surprised to learn that the problems are at least as serious in West Africa. The problems are being studied, particularly by the geologist Frank Simpson of the University of Windsor in Canada. However, most African governments are too poor and too understaffed to do much about them. I am not aware of any large American or United Nations projects to address soil erosion at present.

As I learned when I worked in southern Mexico, the underlying geology very often plays a role in the location and pattern of soil erosion. In Nigeria's Enugu state, major gullies are concentrated in areas with highly friable sandstones while about 65 per cent of the entire state is affected by sheet erosion. Climate and land use play the largest roles in triggering erosion, and the latter is something that human societies can control and hopefully also remedy the effects of. Our history here in the southeastern United States probably represents an extreme as far as intensive row-crop agriculture which has not been equaled elsewhere in the world. On the other hand, our climate is subtropical with somewhat lighter downpours compared to those in the tropical rainy season.

An article in "The Earth Times" summarizes soil erosion in sub-Saharan Africa and recommends an interesting means of controlling it which has been used in southern Africa. Vetiveria zizanoides, a grass native to tropical parts of India, holds the soil in place with its strong roots and also retains moisture that normally gushes off the land in flash floods. In addition to its proven value for erosion control, the grass is thought to have medicinal properties by Ayurvedic herbalists. It has also been used as a famine food in northern Nigeria, where it apparently already grows wild. I would love the opportunity to try making use of it somewhere in tropical Africa in an experimental study. It cannot possibly turn out as badly as our experience with the notorious kudzu vine here in the southeastern United States, also initially thought to be useful for controlling soil erosion.

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