sustainable development. The Commission defined sustainable development as:
"…development that meets the needs of the present without compromising the ability of future generations to meet their own needs…
physically and biologically. Two main problems are associated with soil erosion:
the very fertile top soil is washed away to rivers while,
deposition of erosion is a major source of air and water pollution.
Box 2: Sustainable agriculture
The enthusiastic response to “sustainable agriculture” by scientific community and policy makers is due to severe problems of soil and environmental degradation, pollution of water and environment, and over-dependence on non-renewable sources of energy. However, sustainability is often perceived as a moral or an ethical issue which has taken on an emotional air. Consequently, the topic of sustainability has become a political issue rather than a practical science, a religious myth rather than a generalizable concept, and an interesting theme to discuss and debate rather than a measurable system to evaluate and quantify.
In view of perpetual food deficit and severe problems of soil and environmental degradation in sub- Saharan Africa, sustainable agriculture is not necessarily synonymous with low-input organic or regenerative agriculture in this region. Scientifically speaking, ecosystems utilized by human societies are only sustainable in the long-term if the outputs of the components produced balance the input into the system. Because demand for output from agricultural ecosystems is greater now than ever before, and it is rapidly increasing due to high demographic pressure, no-input or even low-input agriculture is a non-solution. The issue to be addressed, however, is how to balance the inputs required so as to maximize efficiency and cost effectiveness of inputs, reduce risks of soil and environmental degradation, maximize the per capita productivity, and maintain or sustain an increasing trend in productivity.
It should be emphasised that the concept has "needs" as the key issue and particularly reaching the poorest parts of the world by eradicating poverty and planning for the needs of future generations by preserving natural resources and protecting the environment.
Following the Commission's work, a series of international conferences on environmental issues have been held: the UN Conferences of Rio de Janeiro in 1992 and Kyoto (Japan) in 1997 on environment and the development. They were both meant to advance Agenda 21 whose content covers eradication of poverty and protection of environment, with emphasis on sustainable development in developing countries.
Soil conservation is important among global environmental and resource concerns. Sustainability in terms of soil conservation implies utilisation of soil without wastage or depletion, so that it is possible to have a continuous high level of crop production (Schwab et al. 1995). Soil and water resources of our planet are finite and are under already intensive use and misuse. Soil is being eroded at an extreme rate. Cultivated fields, overgrazed pastures, and deforested lands are suffering from erosion. An eroded soil is degraded chemically,
Soil erosion is therefore a potential environmental problem and erosion control is essential in maintenance of crop productivity of the soil as well as to control sedimentation and water pollution.
The sub-Saharan Africa situation
Sub-Saharan Africa (SSA) has a population estimated at about 382 million in 1982, 433 million in 1986, and 490 million in 1990. At an annual rate of increase of 3.2% per year, the population is expected to approximately triple from 433 million in 1986 to 1263 million by the year 2000. The population may eventually stabilize at 10 times its present number (Table 1).
The region is characterized by a huge diversity of climate, soils, geology, hydrology, topography, ethnic groups and cultural heritage. Using Thornwaite’s classification, about 37% of Africa is arid, 13% is semiarid, 23% is sub- humid, and another 13% is humid. Arid and semiarid regions are characterized by low, erratic and highly variable rainfall. Depending on these ecological regions, the climax vegetation varies widely depending on the amount and distribution of rainfall.
This paper is published in: Kaumbutho P G and Simalenga T E (eds), 1999. Conservation tillage with animal traction. A resource book of the
Animal Traction Network for Eastern and Southern Africa (ATNESA). Harare. Zimbabwe. 173p. A publication supported by French Cooperation, Namibia. For details of ATNESA and its resource publications, see http://www.atnesa.org