Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Consuming the savings : water conservation in a vegetation barrier system at the Central Plateau in Burkina Faso

Auteur : Spaan, W.

Université de soutenance : Wageningen Universiteit

Grade : Doctor Thesis 2003

Sommaire partiel
The vast majority of land users at the Central Plateau of Burkina Faso make a living by farming small plots, where mainly staple crops are produced for subsistence use. Both area interventions and line interventions comprising indigenous techniques as well as introduced techniques can be encountered at the Central Plateau and have proved to be effective. There is a preference for semipermeable line measures that slow down runoff and prevent water logging in wet periods. In order to ascertain the rationale behind the choice of soil and water conservation measures and the implementation strategy, five large soil and water conservation projects in three Sahelian countries have been investigated. The choice of technology and the way of implementation differed greatly between projects. This was attributable more to the preference of donors and projects than to any physical, socio-economic and agronomic differences. On the basis of project performances, a recommendable strategy for farmers’ fields appeared to be the use of the local zay technique to achieve a short-term improvement, and to combine this with stone lines or vegetation barriers for a long-term effect. Low adoption rate of soil and water conservation (SWC) measures in erosion-prone areas is often ascribed to the high investment costs of measures. The costs of these measures may seem modest in comparison to costs for infrastructure, but they are often too high for the individual subsistence farmer, especially in marginal semi-arid zones in the Sahel. Investment costs are highest for stone rows, whereby the transport of stones requires substantial inputs of labour and means of transport. Vegetation barriers are less costly, but have the disadvantage that they need to be planted in the rainy season, when agricultural production activities have the highest priority. A major reason why farmers consider the costs prohibitive relates to the uncertain nature of the benefits. These benefits comprise of several elements, some of which may have immediate effect (e.g. moisture retention), but most of which occur only gradually over a long period of time, and are hard to assess and even harder to quantify. In a qualitative multi-criteria analysis stone rows showed the best results, and this was also the measure that with the help of development projects, has been most often applied at the Central Plateau in Burkina Faso. However, vegetation barriers, which have not yet been greatly promoted come a close second and are the best solution in areas where stones are scarce or not available. This conclusion was the starting point of the water conservation research by means of vegetation barriers. The on station field experiment was set up to evaluate the effectiveness of vegetation barriers for soil and water conservation under semi-arid conditions at the research station of the Institute de Développement Rural (IDR) at Gampela. Seven local plant species (grasses : Andropogon gayanus, Vetiveria zizanioides ; woody species : Acacia nilotica, Guiera sengalensis, Piliostigma reticulatum, Ziziphus mauritiana ; and a succulent : Agave sisalana) were planted on a 2 % slope of a sandy loam (Chromic Luvisol), in 21 plots of 20 x 20 m as conservation barriers, along the contour.

Mots clés : WATER CONSERVATION / WATER USE / BARRIERS / VEGETATION / BURKINA FASO / EROSION CONTROL / SOIL CONSERVATION / FARMING SYSTEMS

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