Do the Emerging Methods of Digital Soil Mapping Have Anything to Learn from the Geopedologic Approach to Soil Mapping and Vice Versa?

Abstract

The use of soil maps and the feasibility of the existing soil survey procedure are often questioned by both surveyors and users. Thanks to the advances in the fields of remote sensing (RS) and geographic information system (GIS), a new trend – digital soil mapping – is emerging which might have answers to some of the questions. With a glance to some of the definitions and concepts, such as ‘what is a soil?’ and ‘what is the content of a soil map?’ we intend to highlight the complexity of the soil and its mapping. At the same time, we apply some of the geopedologic-oriented techniques of the digital terrain modelling to soil mapping in order to show the role of geomorphology in the mapping. The exercise was carried out as case studies in several areas in Thailand. Various soils at subgroup levels (Fluventic, Arenic, Aquic, Aeric, Ultic, Ustic, Vertic) belonging to the soil orders Entisols, Mollisols, Inceptisols, Alfisols, and Ultisols occur in different geomorphic surfaces, following well the physiographic setup of the landscapes. The case studies demonstrate the conventional predictive mapping (the ITC approach) and the geopedologic approach to soil survey, based on parameterisation of the soil-forming factors and their integration: in one case through applying decision trees, followed up by a statistical validation, and in another case by means of Artificial Neural Network (ANN). It is hoped to open up a discussion, which should lead to (1) clarifying the term ‘digital soil mapping’ and (2) finding out whether or not the shortcomings of the conventional approach of soil mapping can be recovered using the new trend and does the new trend suggest changes in the current definitions and concepts.