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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
Phone +33 1 43 94 44 00
Fax +33 1 43 94 44 91

CONTRACT TS2- A -146