BackgroundIn Sub-Saharan Africa, 40% of children under five years in age are chronically undernourished. As new investments and attention galvanize action on African agriculture to reduce hunger, there is an urgent need for metrics that monitor agricultural progress beyond calories produced per capita and address nutritional diversity essential for human health. In this study we demonstrate how an ecological tool, functional diversity (FD), has potential to address this need and provide new insights on nutritional diversity of cropping systems in rural Africa.Methods and FindingsData on edible plant species diversity, food security and diet diversity were collected for 170 farms in three rural settings in Sub-Saharan Africa. Nutritional FD metrics were calculated based on farm species composition and species nutritional composition. Iron and vitamin A deficiency were determined from blood samples of 90 adult women. Nutritional FD metrics summarized the diversity of nutrients provided by the farm and showed variability between farms and villages. Regression of nutritional FD against species richness and expected FD enabled identification of key species that add nutrient diversity to the system and assessed the degree of redundancy for nutrient traits. Nutritional FD analysis demonstrated that depending on the original composition of species on farm or village, adding or removing individual species can have radically different outcomes for nutritional diversity. While correlations between nutritional FD, food and nutrition indicators were not significant at household level, associations between these variables were observed at village level.ConclusionThis study provides novel metrics to address nutritional diversity in farming systems and examples of how these metrics can help guide agricultural interventions towards adequate nutrient diversity. New hypotheses on the link between agro-diversity, food security and human nutrition are generated and strategies for future research are suggested calling for integration of agriculture, ecology, nutrition, and socio-economics.

We describe the concept, strategy, and initial results of the Millennium Villages Project and implications regarding sustainability and scalability. Our underlying hypothesis is that the interacting crises of agriculture, health, and infrastructure in rural Africa can be overcome through targeted public-sector investments to raise rural productivity and, thereby, to increased private-sector saving and investments. This is carried out by empowering impoverished communities with science-based interventions. Seventy-eight Millennium Villages have been initiated in 12 sites in 10 African countries, each representing a major agroecological zone. In early results, the research villages in Kenya, Ethiopia, and Malawi have reduced malaria prevalence, met caloric requirements, generated crop surpluses, enabled school feeding programs, and provided cash earnings for farm families.

Losses of carbon ͑C͒ stocks in terrestrial ecosystems and increasing concentrations of greenhouse gases in the atmosphere are challenges that scientists and policy makers have been facing in the recent past. Intensified agricultural practices lead to a reduction in ecosystem carbon stocks, mainly due to removal of aboveground biomass as harvest and loss of carbon as CO 2 through burning and/or decomposition. Evidence is emerging that agroforestry systems are promising management practices to increase aboveground and soil C stocks and reduce soil degradation, as well as to mitigate greenhouse gas emissions. In the humid tropics, the potential of agroforestry ͑tree-based͒ systems to sequester C in vegetation can be over 70 Mg C ha -1 , and up to 25 Mg ha -1 in the top 20 cm of soil. In degraded soils of the sub-humid tropics, improved fallow agroforestry practices have been found to increase top soil C stocks up to 1.6 Mg C ha -1 y -1 above continuous maize cropping. Soil C accretion is linked to the structural development of the soil, in particular to increasing C in water stable aggregates ͑WSA͒. A review of agroforestry practices in the humid tropics showed that these systems were able to mitigate N 2 O and CO 2 emissions from soils and increase the CH 4 sink strength compared to cropping systems. The increase in N 2 O and CO 2 emissions after addition of legume residues in improved fallow systems in the sub-humid tropics indicates the importance of using lower quality organic inputs and increasing nutrient use efficiency to derive more direct and indirect benefits from the system. In summary, these examples provide evidence of several pathways by which agroforestry systems can increase C sequestration and reduce greenhouse gas emissions.

Summaryobjective To demonstrate the feasibility, acceptability and cost of home-based HIV testing and to examine the applicability of the model to high HIV prevalence settings.methods Quantitative, qualitative and cost data were collected during a home-based HIV testing program in a high-prevalence rural area of Kenya; data on age, gender and marital status along with HIV test results were collected. This was complemented with qualitative research including key informant interviews with counselors and program managers to highlight experiences and challenges. Direct costs of the interventions were estimated through the review of budgets and monthly expenditure sheets.results Of 3180 15-49-year olds exposed to a community awareness campaign, 2033 (63.9%) agreed to be visited by counselors, of whom 1984 (97.6%) agreed to be tested and receive the results. Adult HIV prevalence was 8.2% and married women were 4.8 times more likely to be HIV-positive than those never married. Counselors reported feeling welcomed and noted the enthusiasm of the community towards testing. The total cost of the exercise was $17 569. The program cost was $2.60 for each of the 6750 community members, $5.88 for each person tested, and $84 per positive case detected.conclusion This study suggests that home-based HIV testing is feasible with high uptake, and has the potential to substantially expand access to HIV testing services. There is a strong economic case for the extension of such a screening program to other communities.

Potential interactions between food production and climate mitigation are explored for two situations in sub-Saharan Africa, where deforestation and land degradation overlap with hunger and poverty. Three agriculture intensification scenarios for supplying nitrogen to increase crop production (mineral fertilizer , herbaceous legume cover crops— green manures —and agroforestry—legume improved tree fallows ) are compared to baseline food production, land requirements to meet basic caloric requirements, and greenhouse gas emissions. At low population densities and high land availability, food security and climate mitigation goals are met with all intensification scenarios, resulting in surplus crop area for reforestation. In contrast, for high population density and small farm sizes, attaining food security and reducing greenhouse gas emissions require mineral fertilizers to make land available for reforestation; green manure or improved tree fallows do not provide sufficient increases in yields to permit reforestation. Tree fallows sequester significant carbon on cropland, but green manures result in net carbon dioxide equivalent emissions because of nitrogen additions. Although these results are encouraging, agricultural intensification in sub-Saharan Africa with mineral fertilizers, green manures, or improved tree fallows will remain low without policies that address access, costs, and lack of incentives. Carbon financing for small-holder agriculture could increase the likelihood of success of Reducing Emissions from Deforestation and Forest Degradation in Developing Countries programs and climate change mitigation but also promote food security in the region.

[1] The contribution of different land-use systems in the humid tropics to increasing atmospheric trace gases has focused on forests, pastures, and crops with few measurements from managed, tree-based systems that dominate much of the landscape. This study from the Peruvian Amazon includes monthly nitrous oxide and methane fluxes from two cropping systems, three tree-based systems, and a 23-year secondary forest control. Average N 2 O fluxes from the cropping systems were two to three times higher than the secondary forest control (9.1 mg N m À2 h À1 ), while those of the tree-based systems were similar to the secondary forest. Increased fluxes in the cropping systems were attributed to N fertilization, while fluxes from the tree-based systems were related to litterfall N. Average CH 4 consumption was reduced by up to half that of the secondary forest (À30.0 mg C m À2 h À1 ) in the tree-based and low-input cropping systems. There was net CH 4 production in the high-input cropping system. This switch to net production was a result of increased bulk density and increased soil respiration resulting in anaerobic conditions. Reduced rates of N 2 O emissions, similar CH 4 consumption, and high C sequestration rates in these tree-based systems compared with mature forests, coupled with the large area of these systems in the humid tropics, may partially offset the past effects of deforestation on increased atmospheric trace gas concentrations. In contrast, cropping systems with higher N 2 O emissions, substantially reduced CH 4 consumption or even net CH 4 emissions, and little C sequestration exacerbate those effects.

SignificanceUnderstanding relationships between poverty and environment is crucial for sustainable development and ecological conservation. Annual monitoring of socioeconomic changes using household surveys is prohibitively expensive. Here, we demonstrate that satellite data predicted the poorest households in a landscape in Kenya with 62% accuracy. A multilevel socioecological treatment of satellite data accounting for the complex ways in which households interact with the environment provided better prediction than the standard single-buffer approach. The increasing availability of high-resolution satellite data and volunteered geographic data means this method could be modified and upscaled in the future to help monitor the sustainable development goals.

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