Exploring the agricultural landscape diversity-food security nexus: an analysis in two contrasted parklands of Central Senegal

International audienceCONTEXT: Fostering diversity within agricultural systems can substantially contribute to improved food security among smallholder farmers. Agroforestry parklands are diverse agricultural landscapes where trees can provide an array of ecosystem services. Previous studies analyzing the agricultural landscape diversity-food security nexus in agroforestry parklands have only considered tree cover. OBJECTIVE: We propose an original empirical approach that combines the analysis of spatial data on agricultural landscape diversity with agricultural field monitoring and household surveys. These three sources of data were used to scrutinize the direct and indirect contributions of agricultural landscape diversity to food availability and food access. METHODS: Millet yield was used as a proxy for food availability, and household food access was approximated using the Household Food Insecurity Access Scale (HFIAS) indicator. Two contrasted agroforestry parklands of Central Senegal were chosen as case studies. Firstly, we used a Gradient Boosting Machine (GBM) algorithm to disentangle the relative contribution of landscape diversity, biophysical and crop management variables in explaining millet yield variability. Secondly, we investigated the pathways linking agricultural landscape di-versity to HFIAS using a Correlation Network Analysis (CNA). RESULTS AND CONCLUSIONS: The GBM model explained 77% and 84% of millet yield variability for the two parklands, respectively, with landscape diversity variables accounting for 53% and 47% of relative influence. Among the landscape diversity variables, tree species richness and tree density were the most important ones. Millet yield was positively associated with tree density in the Nioro site until a threshold of 5 trees/ha, and with tree species richness in the two sites. The CNA showed that greater tree cover and larger tree patches were moderately correlated with HFIAS. This suggests that tree species with large crown, as it the case for most fruit bearing tree species in the region, are the main species contributing directly to food access. Agricultural land-scape diversity contributed mainly indirectly to household food access through an "agroecological pathway", i.e. by the provision of ecosystem services regulating and supporting crop production. SIGNIFICANCE: Using an integrated landscape approach relying on up-to-date remote sensing data and recent advances in data analysis methods, our study shows that tree species diversity matters as much as the amount of tree cover for the production of food, and it can contribute to improve food security. We bring a more nuanced picture of the contribution of agricultural landscape diversity to food security suggesting that land management policies supporting food security should consider both tree density and tree species diversity to optimize the co -benefits of trees for the different food security dimensions

Soil fertility management in sub-Saharan Africa

Published online: 04 May 2017Most of the population in sub-Saharan Africa depends on agriculture for livelihood, which is mainly practiced by resource-constrained smallholder farmers. Due to persistent low crop yields, food and nutrition insecurity, farmers have been opening new lands through deforestation or encroachment into marginal lands where possible, seeking for additional yields, which has aggravated soil erosion, land degradation, and eutrophication of water bodies. Adoption of integrated soil fertility management practices in the smallholder farming systems has been affected by several factors including poor access to improved agricultural inputs, poor understanding of the practices and their benefits, and importantly limited financial capacity. Here we review challenges of soil fertility management in the smallholder farming systems of sub-Saharan Africa. Our major findings are: (1) most countries have not been able to meet the fertilizer target of 50 kg nutrients ha−1 by 2015 in the 2006 Abuja Declaration; over 65% of the smallholder farmers have not used fertilizer and 75% of the agricultural soils have been affected by nutrient depletion. (2) Poor agricultural practices have resulted in an average annual nutrient loss of 50 kg ha−1, which represented an equivalent of US$ four billion lost in 2008 and an estimated economic cost of up to 18% of the gross domestic product in addition to eutrophication of water bodies. (3) Value cost ratios of agricultural inputs that are less than three are common, which has limited the profitability of integrated soil fertility management practices. (4) Proliferation of fake agricultural inputs has been reported in over 40–60% of the cases as a consequence of poor enforcement of quality standards. (5) In addition to blanket recommendations, fertilization has focused on nitrogen, phosphorus and potassium, with little emphasis on secondary and micro-nutrients as well as organic amendments or liming materials in acid soils, which has generally resulted in poor crop responses or low yield increments. (6) Effective adoption of integrated soil fertility management would result in at least doubling the current nutrient agronomic use efficiency in the smallholder farming systems and reduction of the actual yield gap averaged to more than 300% for cereal and legume crops. Based on these findings, operationalization of supportive policies to increase adoption of good agronomic practices and investment in research to develop solutions appropriate to smallholder farmers should be recommended