The challenges of collating legacy data for digital mapping of Nigerian soils

It is well known that the world is rich with soil data resulting from the efforts of past soil surveys. However, the majority of these data is largely unused. These legacy soil data come in the form of soil maps, soil survey reports, soil profile descriptions, and/or in the format of antiquated “card catalogue”. These data provide many benefits including soil information preservation or as a major component of national environmental monitoring or as the only source of meaningful soil information for Digital Soil Mapping (DSM) in many of data-scarce countries of the developing world. These benefits call for the rejuvenation of these data. In Nigeria, as one of the data-poor countries in terms of modern soil digital soil databases, there is a preponderance of largely untapped legacy soil data as a result of her rich history of soil surveys. This paper provides an account of the challenges faced in the course of the renewal of the Nigerian legacy soil data for the purpose of DSM. In telling this account, we briefly review the processes involved. We then explore the historical soil surveys in Nigeria leading to the synthesis and discussion of the challenges of the processes used for the capture and renewal of the legacy soil data including how the challenges were overcome. This approach is now widely known among soil scientists as digital soil mapping (DSM). Based on the definition by Lagacherie & McBratney (2007), DSM constitutes the processes involved with “the creation and population of spatial soil information systems by the use of field observational methods coupled with spatial and non-spatial soil inference systems”. As has been demonstrated by many studies (e.g., Bui & Moran 2001; McBratney, et al, 2003; Mayr et al., 2008), soil legacy data have a major role to play in DSM, especially in the case of the soil data-poor countries. Nigeria, as one the data-poor countries, is rich in soil surveys since the colonial time, especially post-colonial times (FDALR, 1990). There are currently known hundreds of soil surveys at various scales—ranging from farm levels to national scale. The challenge is how they can be captured and transformed into databases that may be used for temporal trend analysis and for a digital soil mapping program. To achieve these goals is challenging