Nick C. van de Giesen

Effects of charcoal production on maize yield, chemical properties and texture of soil

The effects of charcoal production on soil textural and chemical properties were investigated in Ejura, Ghana. The aim was to study the effects of heating and charcoal residue on maize yield, soil texture and soil chemical properties. Composite samples were taken from the 0–10xa0cm layer of soil at charcoal-making sites and from adjacent fields (control). Twelve sites were randomly selected for the study across the range of the Kotokosu watershed. Maize was planted in four selected locations on charcoal site soils (CSS) and adjacent field soils (AFS) to assess the impact of charcoal production on crop yield. There was a significant increase in soil pH, base saturation, electrical conductivity, exchangeable Ca, Mg, K, Na and available P in the soil at the kiln sites as compared to the adjacent soils. A relative change of up to 329% was observed in K while organic C and total N decreased by 9.8% and 12.8%, respectively. Organic C and total N were highly correlated ( P <0.01) and both parameters significantly ( P <0.05) depended on clay minerals in the soils. Soil texture was also modified with a significantly higher sand content and lower clay fraction in the CSS. The grain and biomass yield of maize increased by 91% and 44%, respectively, on CSS as compared to AFS. Further research to ascertain the long-term effects of charcoal production on the soil environment and the fertility of tropical soils is needed.

An empirical malaria distribution map for West Africa

The objective of this study was to produce a malaria distribution map that would constitute a useful tool for development and health planners in West Africa. The recently created continental database of malaria survey results ( MARA/ARMA 1998 ) provides the opportunity for producing empirical models and maps of malaria distribution at a regional and eventually at a continental level. This paper reports on the mapping of malaria distribution for sub‐Saharan West Africa based on these data. The strategy was to undertake a spatial statistical analysis of malaria parasite prevalence in relation to those potential bio‐physical environmental factors involved in the distribution of malaria transmission intensity which are readily available at any map location. The resulting model was then used to predict parasite prevalence for the whole of West Africa. We also produced estimates of the proportion of population of each country in the region exposed to various categories of risk to show the impact that malaria is having on individual countries. The data represent a very large sample of children in West Africa. It constitutes a first attempt to produce a malaria risk map of the West African region, based entirely on malariometric data. We anticipate that it will provide useful additional guidance to control programme managers, and that it can be refined once sufficient additional data become available.

The relationship between Anopheles gambiae density and rice cultivation in the savannah zone and forest zone of Côte d'Ivoire

In 13 villages in the savannah zone and 21 villages in the forest zone of Côte dIvoire, the biting density of the principal malaria vector, Anopheles gambiae, was studied as a function of rice cultivation in the inland valleys in a 2‐km radius around each village. In the savannah villages, during the main season cropping period, surface water on rice‐cultivated and to a lesser extent on uncultivated inland valleys seems to contribute strongly to the A. gambiae population density. For the off‐season cropping period (which starts after the first light rains in the savannah zone), correlations were weaker. Breeding sites other than in inland valleys may play an important role in the savannah zone. In the forest zone, however, the A. gambiae population density was strongly correlated with the surface water availability (SWA) in the rice‐cultivated inland valleys, whereas the correlation with the SWA in other (uncultivated) inland valleys was weak. The requirement of sunlit breeding sites for A. gambiae might explain this difference between zones. In the forest zone, only inland valleys cleared for rice cultivation meet this requirement, whereas all other inland valleys are covered with dense vegetation. In the savannah zone, however, most undergrowth is burnt during the dry season, which permits sunlight to reach puddles resulting from the first rains.

The GLOWA Volta project: Integrated assessment of feedback mechanisms between climate, landuse, and hydrology

Water management issues critical to the Volta Basin are discussed in this paper. An introduction to the Volta Basin and its hydrological characteristics provides the necessary background. Hydropower production for urban areas and irrigation development in rural areas compete for water resources. The paper introduces the GLOWA Volta project and presents details highlighting the project’s integrative approach. In order to address water-policy issues, the GLOWA Volta Project seeks to develop a scientifically sound Decision Support System. The main premise of the GLOWA Volta investigation is that changes in landuse may have important, yet unknown, effects on the hydrological cycle of the basin. To predict future water availability, landuse change, driven by physical and social factors, needs to be predicted as well. In order to illustrate the different ways in which landuse affects the movement of water over the surface and through the atmosphere, three examples are given. The first example treats the indirect and direct effects of changes in soil moisture on the atmospheric circulation. In the second example, the high sensitivity of surface water availability with respect to rainfall is determined. The final example shows the increase in dam building activity in the basin which has a direct but rather limited impact on availability of water resources downstream.