Mapping Beyond The Solum: Challenges And Some Solutions

Digital soil mapping is typically concerned with predicting standard soil properties (e. g. pH, texture, etc.) within the upper 2 m, or the solum. It relies on data collected close to the soil surface with relative ease using routine survey methodology, or pragmatically, incorporates legacy data that has been collected using standardised survey protocols. Increasingly however, we need to look beneath the solum to understand key landscape processes that operate in this zone, the regolith, which comprises all the horizons above the bedrock. The GlobalSoilMap specifications recognise this need, and will map depth to bedrock globally as part of the standard suite of mapping products. How then do you conduct digital mapping in the regolith when deep drill sampling is expensive, and the legacy data alternative is problematic because it is unreliable because it has been collected using non-standardised drilling methods and description protocols? This paper addresses issues of mapping depth to bedrock using a pilot project from South Australia that applied environmental correlation as a case study. The key issues highlighted here include: a lack of standards in describing regolith material; challenges with filtering large deep drilling legacy data sets (e.g. only similar to 2.5% of >22 000 deep drilling legacy data was useable in the pilot project); and that as depth increases the connection between what you see on the surface and what is at depth becomes increasingly tenuous.