To halt land degradation in sub-Saharan Africa - Institut de recherche pour le développement (IRD)

The IRD is closely involved in the Desert Margins Programme, whose aim is to halt land degradation in sub-Saharan Africa and open the way to sustainable farming there. The programme is supported by the United National Environment Programme and the World Environment Fund.

More than 120 million people in the countries of the sub-Saharan African desert fringe depend on crop farming, livestock and natural resources for their survival. But low rainfall, recurrent droughts and the spread of extensive farming have resulted in widespread destruction of plant cover and consequent soil erosion. The Desert Margins Programme started up in 2003. Its purpose is to help these populations restore degraded land through active research conducted in partnership, and to build up their competencies in managing fragile ecosystems.

IRD researchers and their partners in the national institutes of Senegal and Burkina Faso have been studying the methods that Sahelian farmers use to regenerate degraded soils. A particular example is the zai system, in which the crop is sown in shallow pits dug out to concentrate water and nutrients. The researchers have made a comparative typology of farms according to soil type, the availability of organic matter and the soil rehabilitation methods used.

Examining ways to add organic matter to the soil and so increase farm output in a sustainable manner, they have been testing local composting methods and the factors that determine the agronomic quality of the finished compost. They have assessed the fertilising properties of different types of compost in greenhouse trials with common crop species – maize, sorghum, millet and cowpea. Their findings confirm that it is important to control moisture levels in the materials during the composting process, and that adding natural tricalcium phosphate, which is available in the region, could further improve the performance of the compost while beneficially increasing phosphate levels in the soil. Outreach sessions have been held in villages to help farmers improve their composting methods and fertiliser use.

To improve ecological management of degraded soils, the researchers have been studying the possibility of better integrating trees with crops. With the farmers they have been monitoring a zai agro-forestry system developed from bare soil, and they have studied the use of forest produce such as medicinal plants and wild foods.

The project has also shown by adding soil that has been worked over by termites one can significantly enhance symbiosis between ligneous species and fungi, increasing the plants’ resistance and growth rates. This effect has also been successfully tested in market garden crops (IRD patent applied for).

Today, innovative practices such as erosion control structures in the fields combined with new cropping practices have succeeded in increasing tree and herbaceous cover in
some parts of the Sahel, shedding a more optimistic light on the usually depressing picture of constant deterioration in the Sahel’s dryland ecosystems.