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Basé sur des cas d'étude au Sénégal, ce chapitre dresse le bilan de 15 années de recherches sur le fonctionnement des sols d'agrosystèmes associant plantes cultivées (mil-arachide) et arbustes natifs au Sahel. Les travaux, publiés pour la plupart, ont montré que Guiera senegalensis et Piliostigma reticulatum redistribuent l'eau dans le sol, stimulent les microorganismes du sol et génèrent des îlots de fertilité au bénéfice de la culture associée. Ainsi, les rendements des cultures sont augmentés, y compris en absence de fertilisants : jusqu'à +137 % pour le mil en présence de P. reticulatum à Nioro-du-Rip. Cela justifie l'intérêt de maintenir ces arbustes dans les champs en appliquant une gestion agroécologique.

In the context of environmental and socio-economic changes, sub-Saharan African countries will have to ensure their food security, while reducing its environmental footprint. It is assumed that to take up the challenge of climate smart agriculture, it is necessary to intensify ecological processes of agrosocioecosystems at the scales of the soil-plant system, the farmers' fields and the agro-ecosystems and also the territories. This ecological engineering approach is the framework of the researches led by the IESOL International Joint Laboratory "Intensification of agricultural soils in West Africa". For instance, studies concerning the management of organic matters and the nutrients cycles in peri-urban agriculture and in Pearl Millet cropping systems will be exposed. We tested intensification practices as crop livestock integration, urban waste recycling, more efficient fertilizer use, and degraded lands restoring in Senegal and Burkina Faso. This will lead us to propose some rules of thumb of future innovations in semi-arid agrosystems based on the recycling and the conservation of organic matter and nutrients. (Texte intégral)

Soil degradation and fertility loss pose severe threats to the livelihood of farmers in sub-Saharan regions. Due to the need for land, continuous cultivation with staple food has gradually replaced previous shifting cultivation systems, so that fallow periods have considerably reduced and no longer fulfill their soil regeneration role. Here we explore the use and management of native woody resources for providing an in situ renewable organic amendment as a basis for increasing soil carbon and biological status, thus sustaining fertility, enhancing water capture and utilization and therefore buffering climatic stress. In areas such as the central plateau in Burkina Faso, slash- and drought-tolerant shrub species are commonly present in farmers' fields. Cut branches from these shrubs are sometimes placed on degraded soils as part of traditional soil restoration practices. Moreover, shrubs tend to intercept sediments and leaves and promote biological activity whereby they may form fertility islands of increased crop yield. We will review available data on traditional practices and current co-innovation efforts and outline first results from an EU-supported project we have initiated in Burkina Faso and Senegal (ERA ARD WASSA). This project is investigating if a sustainable use of native woody resources could be made, in combination with other organic sources such as crop residues or manure, to amend soils and help preserving fertility at the whole field scale. Through experimental plot trials and farmers' fields surveys, we are evaluating how woody residues use and management practices may impact agronomic performance and soil biological processes. Crop response to use of ligneous material will be linked with the availability and distribution of woody resource in the landscape, and the ways it could be eventually increased and sustainably managed. The socio-economic implications of implementing such practices are also considered. (Texte intégral)