IRD/Eco&Sols, France: Laurent Cournac,

Managing soil organic matter (SOM) is a crucial issue in Sub Saharan Africa, especially in arid to semi-arid regions where permanent crop cultivation and insufficient fallow periods may lead to severe SOM depletion. Organic fertilization is one of the main options for such management but it is often limited by the availability of resources. Woody residues (small branches and leaves) from tree pruning or shrubs coppicing (i.e. ramial wood, RW) may represent a potential organic resource with limited competition for their use as fuel or forage, and could thus constitute an alternative for amending soil.

Soil amendment with RW has been experimentally explored over the past 20 years and spectacular effects on crop yields have sometimes been reported, but scientific information on this subject and especially integrated studies are scarce. The effect of RW application on SOM and nutrient dynamics, the importance of application modes or of tree species selection, and the impacts on yield are not well understood. Moreover, environmental impact of RW removal on the ecosystem, and conditions for technical, tenurial and cultural integration of tree and shrubs in the farming system are nearly undocumented.

The WASSA project proposes to address these issues through an integrated approach, performed in connection with current woody amendments trials running through projects located in Burkina Faso and Senegal. It will be organized in three operational work packages: WP1 will aim to analyse the agronomic and biological/technical determinants of RW amendment on soil fertility and crop yield, WP2 will aim to analyse RW resource and optimal management practice, WP3 will integrate data from WP1 and 2 and analyse farmers’ current practices together with the likely impacts of RW amendment implementation, to determine the regulatory and technical improvement pathways for optimizing them. A fourth WP will be devoted to project coordination and management.

This research effort will result in an improvement of our understanding of the biological, agronomical and ecological mechanisms determining the impacts of RW amendment. It will provide a knowledge basis for thoroughly assessing and eventually optimizing the benefits of RW application for crops yields. It will also produce a documented conceptual framework for anticipating RW resource availability and ensure its sustainable utilization. These different results of the project will be integrated into a multidisciplinary modelling approach. The resulting models will constitute valuable tools to help in designing optimized RW application schemes and appropriate resource management policies.

The expected impacts of the project are therefore to:

• Provide cost-effective and sustainable alternatives for soil fertility management, based on woody substrates as natural and renewable resources
• Contribute to improving crops yields and agrosystems resilience
• Provide a framework for integrated practice of RW amendments, taking into account resource renewal and competition for use
• Elaborate wood resource management recommendations for stakeholders.

36 months

Laurent Cournac,

IRD/HSM, France: Luc Séguis,
CIRAD/SCA, France: Rabah Lahmar,
CIRAD/BSEF, France: Denis Gautier,
WUR/BFS, Netherlands: Pablo Tittonell,
UO/SVT, Burkina Faso: Edmond Hien,
2iE, Burkina Faso: Rabah Lahmar and Dial Niang, and
Eben-Ezer, Burkina Faso : Edmond Zongo,
ISRA/LNRPV, Senegal: Hassna FOUNOUNE-MBOUP,
Agrhymet, Niger: Mahamadou BELEM,

WASSA factsheet (pdf)