Agroforesterie et services écosystémiques en zone tropicale

Respectueux de l’environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu’ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d’agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu’à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L’ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d’une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l’Est et du Centre, d’autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d’Afrique de l’Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l’IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L’ensemble de ces projets s’articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

The Joint International Laboratory ECLAIRS set up an oceanographic and meteorological buoy, dedicated to monitoring and analysis of the short and long-term changes in climate, atmosphere and marine environment within the Senegal coastal upwelling. The buoy "MELAX" was deployed early 2015 in the heart of the Senegalese upwelling by 30 m-depth at (14,20'N, 17,14'W). Data collected are, for the atmosphere, surface wind, solar radiation, humidity and rain, and for the ocean, temperatures, salinity, and currents (from the surface to the bottom) and oxygen. We present the first year and a half of observations, in particular the relationship between wind, sea surface temperatures, and hydrology. Satellite and model data are used to provide a larger-scale context to the local monitoring

Temporal microbial response to wetting-drying cycles in soils within and outside the influence of a shrub in the Sahel

Piliostigma reticulatum is a native woody shrub found in cropped fields in the Sahel and has been shown to increase crop productivity and soil quality. Frequently occurring drying and rewetting cycles (DRW) may alter the soil quality beneath these shrubs. We investigated the effect of DRW cycles on microbial community in soil beneath and outside the P. reticulatum canopy and the roles of this shrub in the adaptation of the microbial community to abiotic stress. Soils were incubated in a climate controlled chamber for 45 days, after exposure to 10 consecutive days of DRW cycles at 75% of water holding capacity (WHC). Basal respiration, ?-glucosidase activity, microbial biomass carbon (MB C ), and available nitrogen ( NH+4 ; 3NO-3 ) were measured at 2, 30, and 45 days after soil exposed to the DRW cycles. MB C increased significantly two days after the DRW cycles and was greater for soil beneath the shrub canopy compared with soil outside the shrub canopy. PCA analysis based on basal respiration, microbial biomass carbon, available nitrogen, and bêta-Glucosidase activity resulted in a tight clustering in the beneath shrub soil samples. Soils incubated for more than 30 days after DRW cycles had higher available nitrogen content than soils incubated for less than 30 days. Soil from beneath the shrub canopy significantly improved soil resilience based on bêta-glucosidase activity. Soil from beneath the shrub canopy also had higher nutrient levels and greater microbial activity even when subjected to DRW cycles, potentially improving the ability of crops to withstand in-season drought when they are adjacent to shrubs. The work should bring our scientific community into a more comprehensive assessment of potential effects of a crop-shrub intercropping that may allow for increased crop yields in semi-arid ecosystems under drought conditions

Specificity of circulating antigen detection for schistosomiasis mansoni in Senegal and Burundi

The definitive version is available at www3.interscience.wiley.comThe specificity of schistosome circulating antigen detection was determined in negative individuals from two S. mansoni- endemic countries, Senegal and Burundi, and compared with results from Dutch control individuals. A nearly absolute specificity was achieved for circulating anodic antigen (CAA) detection in serum, irrespective of the target population or sample pretreatment method. Circulating cathodic antigen (CCA) detection in serum and urine resulted in a lower specificity than serum CAA detection. Apparent large differences in specificity of CCA detection between countries were mainly due to pretreatment methods. Apparently, the alkaline/heating pretreatment method is not as effective as trichloroacetic acid (TCA) -pretreatment in removing (certain) interfering components, which may vary between populations. In view of the development of the urine CCA assay into a noninvasive screening test, a slightly lower specificity may still be acceptable. For precise epidemiological analyses the highly specific serum CAA assay remains the method of choice

Impact of simulated drought stress on soil microbiology, and nematofauna in a native shrub + millet intercropping system in Senegal

Drought stress strongly affects soil biota and impairs crop production, which under climate change will be exacerbated in semi-arid cropping regions such as the Sahel. Hence soil management systems are needed that can buffer against drought. In West Africa, field studies have found intercropping of millet with the native shrub Piliostigma reticulatum improves soil-plant-water relations, microbial activity and diversity, and suppress parasitic nematodes, which can significantly increase crop yield. However, little information is available on its beneficial or negative effects on soils or crops during water stress. Therefore, the objective was to investigate the impact of P. reticulatum in moderating water stress effects on soil properties and pearl millet (Pennisetum glaucum [L.] R. Br.) productivity. In the greenhouse, soil chemical and microbial properties and millet growth were investigated with a factorial experiment of varying levels of soil moisture (favorable, moderately stressed, or severely stressed water conditions) that was imposed for 55 days on soils containing sole P. reticulatum or millet, or millet + P. reticulatum. The results showed that the presence of P. reticulatum did not buffer soils against water stress in relation to soil chemical and microbial properties measured at the end of the experiment. Severe water stress did significantly decrease the height, number of leaves, and aboveground biomass of millet plants. Additionally, respiration, nematofauna trophic structure and abundance decreased as water stress increased. Lastly, bacterial feeders and plant parasitic nematodes were the most sensitive to severe water stress while fungal feeding nematodes remained unaffected. The results suggested that the intensity of water stress had more negative effects on soil basal respiration rather than soil microbial biomass

The influence of a shrub-based intercropping system on the soil nematofauna when growing millet in Senegal

Woody shrubs commonly co-exist with annual food crops in farmers' fields throughout the Sahel. Management strategies that deliberately include the native shrub Piliostigma reticulatum in Senegalese cropping systems result in soil functioning enhancement that benefits to the associated cereal. The objective of this work was to evaluate shrub effect on soil nematode communities. Soil samples were collected from an experimental design where pearl millet (Pennisetum glaucum) was cultivated alone or with P. reticulatum stands and mulch. Soil nematofauna characteristics were determined and compared with results from soil under pure shrub stands and from bare soil. The analysis of soil nematofauna, characterized by the abundance of different trophic groups and related indices (MI, maturity index; El and SI, enrichment and structure indices), allowed discrimination between treatments with or without shrub presence. The soil nematode community in millet cultivation was dominated by plant feeding nematodes, mainly from the Hoplolaimidae family, but their abundance decreased when P. reticulatum was associated to the cereal. The shrub also impacted other nematode trophic groups. The abundance of opportunistic bacterial feeders (mainly Cephalobidae) was increased in shrub treatments. Further research should explore consequences on cereal nutrition and nematicidal properties of P. reticulatum