Piliostigma reticulatum (DC.) Hochst., an indigenous shrub, forms an important vegetative component of parkland cropping systems in the Sahel; however, its biophysical interactions with soil and crops are not well understood. Therefore, the objectives were to determine the impact of P. reticulatum, under varying fertilizer rates, on crop yield response and soil nutrient dynamics. The experiment had a split‐plot factorial design, where the main plot was shrub (presence or absence) and the subplot was fertilizer rate (0, 0.5, 1.0, or 1.5 times the recommended N–P–K fertilizer rate) applied to a peanut (Arachis hypogaea L.)–pearl millet [Pennisetum glaucum (L.) R. Br.] rotation. In 3 of the 4 yr, P. reticulatum improved or had no effect on crop yields when averaged across fertilizer rates. Overall, millet and peanut biomass and N and P uptake by millet increased in the presence of shrubs and with increasing fertilizer rate. Contrary to P, inorganic N in the soils changed very rapidly, reaching very low levels by the end of the growing season. The N content of soil leachates below the rooting zone was generally lower beneath than outside the shrub canopy, suggesting that the shrub conserves N that is otherwise lost through leaching. Piliostigma reticulatum increased particulate organic matter, indicating that this shrub improved soil quality. These results suggest that P. reticulatum, under nonthermal management and a higher density than typically found in farmers’ fields, has ecological benefits with improved soils and reduced loss of N, which has implications throughout the Sahel.

Two shrub species (Piliostigma reticulatum (D.C.) Hochst (Caesalpinioideae) and Guiera senegalensis J.F. Gmel (Combretaceae) are commonly found in farmers' fields at varying densities in semi-arid Senegal and throughout the Sahel where soils have chronically low phosphorus (P) availability. It seems plausible that shrub litter and the rhizospheres could influence P fractions and other chemical soil properties that affect crop productivity. Thus, a study was done at two sites, on the distribution of inorganic and organic soil P pools, organic C levels, and pH in soil beneath and outside the canopies of P. reticulatum and G. senegalensis (0-30 cm depth). Both sites had low total P ranging from 64 mg P kg −1 to 135 mg P kg -1 , and low extractable PO 4 (resin Pi) (1-6 mg P kg −1 ) with P fractions dominated by NaOH-P. Organic P (Po) made up about 50% of total P, and most of the organic P (>60%) was found in the NaOH-P fractions. The labile P, particularly bicarb-Po was higher in soil beneath shrub canopies (8.4 mg P kg −1 ), than outside the canopy (6.2 mg P kg −1 ). Similarly, C, N and P to a lesser extent, were more concentrated beneath shrub canopies. P. reticulatum soil was dominated by the NaOH-Po fraction, whereas G. senegalensis had higher bicarb-Po at one of the study sites. An index of biologically available organic P (BicarbPo) / (Bicarb-Po +Bicar-Pi+Resin Pi) was >60% and indicates that biological processes represent an important part of P cycling in these shrub ecosystems. The differential ability of shrubs in modifying soil chemical properties under their canopies has major implications for biogeochemical cycling of nutrients and C in sandy soils of semi arid Sahelian ecosystems.

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Whereas Leishmania infantum, the agent of visceral leishmaniasis (VL), is well known in North Africa, very limited data exist on its spread in West Africa, where mainly cutaneous leishmaniasis has been widely reported. Nevertheless, dogs infected with L. infantum were recently found in the Mont Rolland District in Senegal. To provide a better understanding of L. infantum epidemiology in this area, clinical and serological surveys were carried out to determine the seroprevalence of L. infantum-specific antibodies in the human population. In parallel, an analysis of environmental and individual factors associated with Leishmania antigen seropositivity was conducted to identify potential risk factors for exposure. Although no cases of VL were detected within this study, a large part of the population (73/315; 23%) was exposed to infection, with a strong age effect (being >40 years old increased the risk of being seropositive). Moreover, the presence of Nebedaye trees (Moringa oleifera) and infected dogs in the household were factors increasing the risk of exposure in household members. These results may provide important information to identify the still unknown sandfly species involved in transmission.

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This work was carried out to determine the relative importance of the endomycorrhizal and (or) ectomycorrhizal association in species of Casuarina and Allocasuarina. Under axenic conditions, Pisolithus and Scleroderma isolates formed ectomycorrhizas with a mantle and a Hartig net on Allocasuarina verticillata but failed to form a Hartig net on Casuarina glauca. In a controlled soil system, C. glauca was inoculated with the endomycorrhizal fungus Glomus intraradices Schenck & Smith, and A. verticillata was inoculated with Pisolithus albus IR100 Bougher & Smith and (or) G. intraradices. Both symbionts significantly stimulated growth in both plant species. For A. verticillata, its growth response to ectomycorrhizal inoculation was higher than to endomycorrhizal inoculation. When both symbionts were inoculated, antagonism among the fungal isolates was observed with a higher ectomycorrhizal colonization. These results showed that A. verticillata was ectomycorrhizal dependent, whereas C. glauca was endomycorrhizal dependent. From a practical point of view, this study shows the importance of selecting compatible mycorrhizal fungi for developing successful inoculation programmes. In addition, it would help to further research and determine the effect of ecto- and endo-mycorrhizal symbiosis on the formation and function of N2-fixing actinorhizal nodules.

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