Proprietes hydriques des sols dans deux zones a ecosystemes contrastes au Sahel

Les sécheresses répétées du Sahel et la pression de la population ont eu un impact négatif sur l’environnement ont conduit à la dégradation des ressources naturelles. Mais depuis ces deux dernières décennies, l’état des ressources au Sahel est mitigé. C’est ainsi que, dans certaines zones, on parle de la perte de certaines fonctions du sol. Cette étude menée dans le Sahel et dans deux zones à écosystèmes contrastés a porté sur la détermination des propriétés hydrodynamiques et la caractérisation des sols en fonction de l’occupation des terres afin de déterminer la capacité du sol à soutenir certaines fonctions. Elle analyse l’influence de l’occupation des terres sur les propriétés hydriques des sols. Elle a utilisé un échantillonnage de sol, des mesures de densité apparente, d’humidité et l’infiltrométrie à succion contrôlée à trois niveaux de tensions en fonction de l’occupation des terres. L’analyse statistique donne des différences significatives en ce qui concerne la variation de l’argile avec la profondeur, très significatives pour l’analyse texturale en fonction de l’occupation des terres. Pour les propriétés hydriques, seule la conductivité hydraulique à la tension (-5) et la taille des pores par sites donnent une différence significative. Les résultats montrent une dégradation de la texture qui induit celle de la porosité texturale et de forte valeur de conductibilité hydraulique à Koalma.Mots clés : Conductivité hydraulique ; texture du sol ; occupation des terres ; dégradation ; Sahe

Immunogenicity of Fractional Doses of Tetravalent A/C/Y/W135 Meningococcal Polysaccharide Vaccine: Results from a Randomized Non-Inferiority Controlled Trial in Uganda

Meningitis are infections of the lining of the brain and spinal cord and can cause high fever, blood poisoning, and brain damage, as well as result in death in up to 10% of cases. Epidemics of meningitis occur almost every year in parts of sub-Saharan Africa, throughout a high-burden area spanning Senegal to Ethiopia dubbed the “Meningitis Belt.” Most epidemics in Africa are caused by Neisseria meningitidis (mostly serogroup A and W135). Mass vaccination campaigns attempt to control epidemics by administering meningococcal vaccines targeted against these serogroups, among others. However, global shortages of these vaccines are currently seen. We studied the use of fractional (1/5 and 1/10) doses of a licensed vaccine to assess its non-inferiority compared with the normal full dose. In a randomized trial in Uganda, we found that immune response and safety using a 1/5 dose were comparable to full dose for three serogroups (A, Y, W135), though not a fourth (C). In light of current shortages of meningococcal vaccines and their importance in fighting meningitis epidemics around the world, we suggest fractional doses be taken under consideration in mass vaccination campaigns

Effect of the raw materials and mixing ratio of composted wastes on the dynamic of organic matter stabilization and nitrogen availability in composts of Sub-Saharan Africa

The effect of raw materials and their proportions in initial mixtures on organic matter (OM) stabilization and nitrogen (N) availability during pit composting in Sub-Saharan Africa was assessed using biochemical fractionation and laboratory incubations to characterize composts sampled throughout the composting process. Stabilization of OM occurred more rapidly in mixtures with slaughter-house wastes, it was progressive in mixture with household refuses while tree leaves compost remained unstable. Carbon mineralization from compost samples was positively correlated to water soluble and hemicellulose-like organic fractions. Mixtures containing large proportions of household refuses reached the highest stability and total N but available N remained weak. Slaughter-house wastes in the initial mixtures made possible to reach good OM stabilization and the largest N availability. The nature of initial mixing influenced composting parameters, OM stabilization and N availability. it is suggested mixing household refuses and slaughter-house wastes with tree leaves to reach better amending and fertilizer qualities of composts