Rescue and renewal of legacy soil resource inventories: A case study of the Limpopo National Park, Mozambique

• Legacy data renewal may be applied to get the added value out of legacy surveys.
• Data archaeology can discover diverse legacy soil surveys, especially in Africa.
• Positional accuracy can be used to assess boundaries of renewed legacy soil survey.
• Legacy data renewal can be used to identify knowledge gaps and guide resurveys.

Many areas of developing countries are covered by legacy soil surveys, which, however are hardly used, as they are not available in digital form, used outdated standards, and have unknown quality. There have been very few attempts to rescue and renew these surveys, nor are there established criteria for the evaluation of their quality. We therefore decided to test the applicability of the Cornell Adequacy Criteria (CAC) to assess the quality of several renewed soil surveys in or near the Limpopo National Park, Mozambique (centroid: 23° 18′ 55.57″ S, 31° 55′ 16.24″ E), using the concepts of digital soil mapping. The quality was assessed for mapping and monitoring soil organic carbon (SOC), in terms of geodetic control, positional accuracy, map scale, and texture and adequacy of map legend. Metadata was attached to the renewed maps. SOC stocks were estimated qualitatively based on the description of the map units and quantitatively by the measure-and-multiply approach from legacy laboratory measurements. The positional accuracy of georegistration was 13 to 45% of the square root of a Minimum Legible Area (MLA). Point and area-class layers could be created with high positional accuracy. However the index of maximum reduction was high, indicating that the original publication scale could be reduced. Map unit definitions and overall information content of the surveys were adequate. Integration of remotely sensed optical imagery and digital elevation models could be used to derive accurate contours, against which the positional accuracy of contour-based map borders was assessed. Less than 30% of their lengths were within a distance equal to the square root of MLA. These sources could not be used to evaluate internal map borders, due to the subdued topography and major land-use changes since the original survey. Qualitative estimates of SOC are between low and medium, consistent with other studies in this area. The CAC proved to be a useful framework for determining the fitness for use of legacy surveys.