article · Geoderma
Digital soil mapping has gained interest across Africa over the last two decades, yet widespread implementation faces significant technical hurdles. A review of existing work indicates that approximately half of African countries possess a local or national digital soil map, with the majority of studies focusing on local extents. Soil carbon in the topsoil is the most commonly mapped characteristic, while soil hydraulic properties remain rarely documented. Major challenges include low sampling density, spatial clustering, reliance on legacy datasets with positional errors, and unavailable environmental covariates. Furthermore, only eleven percent of investigations report map uncertainty, and almost none collect post-mapping probability samples for validation. While half of the studies intend downstream uses like fertility assessment, delivering actionable soil data to stakeholders remains inadequate. Addressing these issues requires regional capacity building, fresh sampling campaigns, and African-led long-term monitoring systems.
Healthy soils are vital for agriculture, yet accurate African soil data remains sparse, clustered, and frequently out of date. Without reliable maps and validated uncertainties, policymakers and agricultural managers cannot make fully informed decisions. Better mapping methods, alongside sustained local data collection, are essential to establish dependable soil information systems that support food production, resource management, and environmental monitoring across the continent.
Target applications include soil fertility assessment, long-term environmental monitoring, and public land-use planning for governmental institutions and agricultural stakeholders. Because the underlying work is a review identifying significant gaps in data coverage, sampling density, and uncertainty reporting, commercial or operational deployment remains at an early stage. Developing practical services requires investments in new field sampling, legacy data rescue, and improved delivery platforms to make digital soil data directly usable for decision-makers.
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The mapping of soils in Africa is at least a century old. We currently have access to various maps depicting mapping units locally and for the continent. In the past two decades, there has been a growing interest in alternatives for generating soil maps through digital soil mapping (DSM) techniques. There are, however, numerous challenges pertaining to the implementation of DSM in Africa, such as the unavailability of appropriate covariates, age and positional error in the measurements, low sampling density, and spatial clustering of the soil data used to fit and validate the models. This review aims to investigate the current state of DSM in Africa, identify challenges specific to implementing DSM in Africa and the ways it has been solved in the literature. We found that nearly half of African countries had an existing digital soil map covering either a local or national area, and that most studies were performed at a local extent. Soil carbon was the most common property under study, whereas soil hydraulic variables were seldom reported. Nearly all studies performed mapping for the topsoil up to 30 cm and calculated validation statistics using existing datasets but without collecting a post-mapping probability sample. Few studies (i.e., 11%) reported an estimate of map uncertainty. Half of the studies had in mind a downstream application (e.g., soil fertility assessment) in the map generation. We further correlated the area of study and sampling density and found a strong negative relationship. About 30% of the studies relied on legacy soil datasets and had a lack of sufficient spatial coverage of their area of study. From this review, we highlight some research opportunities and suggest improvements in the current methodologies. Future research should focus on capacity building in DSM, new data collection, and legacy data rescue. New initiatives, that should be initiated and led from within the continent, could support the long-term monitoring of soils and updating of soil information systems while ensuring their contextualised usability. This pairs with better delivery of existing DSM studies to stakeholders and the generation of a value-added proposition to governmental institutions. • Half of African countries have an existing digital soil mapping study. • There are numerous challenges for generating soil maps in Africa. • Local initiatives for a sustainable soil data collection is required. • More efforts should be invested in capacity building and soil monitoring systems. • Delivery of detailed soil information to stakeholders is insufficient.
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DOI: 10.1016/j.geoderma.2024.117007
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