Bioreclamation of degraded lands in the Sahel
The Sahel, a vast area stretching from Senegal and Mauritania on the shores of the Atlantic Ocean in the west, to Eritrea in the east, is predominantly sand. Covering an area of over three million square kilometres, the Sahel was once grassland and savanna, with areas of woodlands and shrubs. However, clearing of perennial vegetation by farmers to allow cultivation of the soil, combined with grazing and utilisation of crop residues, has exposed the sandy soil to wind and water erosion and caused the land to become degraded.
As a result, drought and famine have been increasingly common across the Sahel as farmers continue to clear vegetation, allow livestock to overgraze, and endeavour to try to grow crops in extremely poor soils. Many areas are no longer suitable for agricultural production but, in order to support the increased demand for food and income by a growing population, it is vital that these degraded lands are brought back into production.
An initiative to use hardy trees, which grow well in poor soils while yielding a commercially viable product, is the foundation for a regional bioreclamation initiative being promoted by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and partners in western and central Africa.
Using water harvesting techniques
The bioreclamation of degraded lands (BDL) is based on water harvesting techniques for the production of high value crops. Farmers of the Sudano-Sahelian region have developed indigenous techniques, such as the 'demi-lune', or semi-circular micro-catchment. Between the micro-catchments, zaï holes (10-20cm deep planting pits) are dug and filled with manure or compost. Stone lines facilitate water infiltration and trenches catch runoff. More trenches dug every 20 metres down the slope, also help to retain runoff.
Lateritic soil is formed under tropical conditions, indicating that the Sahel was once more tropical. The sandy layer in the Sahel, which may vary from a few centimetres to about 20 metres, covers the lateritic layer, which is relatively permeable to water. However, if the sand is removed and the lateritic soil exposed to alternating sun and rain, a crust forms which significantly reduces rain infiltration.
Two types of laterite exist: soft laterite (known as female) that can be cultivated relatively easily or hard (male) laterite which is more difficult to cultivate. But both are more fertile and hold more water than sandy soils.
These micro-catchments and zaï holes have traditionally been used to grow cereals, such as sorghum and millet. But while yields are increased, production of these low-value crops provides a poor return for the high labour required to establish the demi-lunes.
However, three years of on-station and on-farm research by ICRISAT scientists, joined recently by a researcher from the World Vegetable Centre (AVRDC), has resulted in the creation of a highly versatile and promising system that exploits all the advantages of the laterite layer (see box) over the sandy soil for income generation.
Rehabilitation using hardy trees
In Niger, two tree species are planted in the demi-lunes; the domesticated Ziziphus mauritiana ('Pomme du Sahel') from India, and Moringa stenopetala. The fruit of the Pomme du Sahel is ten times bigger than that of the wild, indigenous Z. mauritiana and the fruit is quickly gaining popularity in the Sahelian region. Moringa is also an important leafy vegetable in Niger and the leaves of M. stenopetala (which originates from Ethiopia) are almost as tasty as those from the locally-used M. oleifera which grows in tropical India.
Other potential BDL trees are sweet tamarind (Tamarindus indica) varieties from Thailand, improved marula (Sclerocaria birrea) varieties from southern Africa and selected high-yielding Sudanese Acacia senegal (gum arabic) varieties, which all have the potential to produce a commercially valuable product. Hardy traditional vegetables are intercropped amongst the trees, including short duration okra (Albemochus sp.); Senna obtusifolia, a traditional vegetable; and Roselle (Hibiscus sabdariffa). Medicinal and forage plants can also be grown to provide additional income until the trees are mature enough to yield an income.
In the Sahel, women are not eligible to own cropland and are economically dependant on the head of the household. However, degraded lands are normally farmed communally and men tend to not reject the allotment of degraded communal lands to women's groups. The BDL initiative could provide a means of ensuring land rights for women although it would require civil society to assist the women to negotiate their claims with village leaders and local government authorities. Men would also be more likely to take an interest in the land once they realise the economic potential of rehabilitation BDL schemes.
The BDL system is still in its infancy and further investigations will be carried out. However, the demand for the approach is high and this year, some 30 BDL plots will be planted in various regions of Niger, impacting on the livelihoods of 1,000 households. If the pilot plantations succeed, the BDL system could provide a means of reclaiming vast areas of unusable land, improving household security, while mitigating the impact of climate change.
With contributions from: Dov Pasternak
Date published: March 2008
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