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Mechanisms of aggregation of topsoils soils poor in expanding clays in Western African savannahs”



A project entitled “Mechanisms of aggregation of topsoils soils poor in 
expanding clays in Western African savannahs” lead by Dr. Gérard Bourgeon, 
Centre de Cooperation International en Recherche Agronomique pour le 
Dévelopment, Département de Cultures Annuelles, (CIRAD-IRAT),France in 
partnership with other scientific institutions in Burkina Faso, Mali 
Netherlands and France was carried out under the European Union (D.G.XII) STD2 
scientific programme.

The aim of the project was: 
- to study the factors and the state of aggregation of the soils in two 
sectors of the sudanian-sahelian tropical zone;
- to reinforce the research capacity of institutions concerned with the 
physics of sandy soils, a very difficult field;
- identification of agronomic techniques able to improve the structure of the 
soils under cultivation. 
In this context the project achieves scientific advance in :

- Doing the geological and pedological characterization of the Saria region in 
Burkina Faso and of the Mobala region at Mali. Tropical ferruginous soils, 
(ustalfs) developed on granite-gneisses and sandstone’s, have been identified. 
These rocks are representative of the lithological conditions of the 
sudan-saheliens regions of West Africa.
- The characterization of the state and of factors aggregation of sandy soils 
, which is very important to conservation and better use of the soils, bearing 
in mind a sustained development-also an objective.
- The quantification, on a landscape scale basis, of the role of the 
pedological characteristics and of cultural practices in soil structure.
-The application of a model which allows to breakdown porosity in textural and 
structural terms, to these tropical soils. This type of model only had been 
applied, before, in clay-silt soils of temperate regions.

This model highlights the differences between the soils structural state in 
respect to the different aspects of agricultural environment, this is, an 
interaction environment-cropping system exists.
The project highlights the necessity for experiments at landscape unit level, 
to allow the generalization of results. Besides that it is suggested the 
introduction of a control, representing the traditional cropping systems of 
the region, when the aim of the experiment is to improve these ones.
Finally, time is a key factor to achieve meaningful results, so the 
experiments must be conduct in the long term.
Several cultural practices were recommended, among them the addition of 
organic matter, and the benefits of its good management, the introduction of 
fallow and gramineous plants for forage, the abolishment of tillage procedures 
currently in use and the application of new types of agricultural implements.
As in others projects the impact of this one depends on the way as the results 
will be passed to the population. Which we think is very important.

Within this project several publications have been issued.

For further information please contact:
Dr Gérard Bourgeon
Centre de Cooperation International en Recherche Agronomique pour le 
Dévelopment, Département de Cultures Annuelles, (CIRAD-IRAT)
45 bis,Avenue de la Belle Gabrielle
94736 Nogent sur Marne, France
CONTRACT TS2- A -146