Where are we with whole regolith pedology? A comparative study from Brazil

Abstract

An integrated knowledge of the soil and its deeper substratum is required when dealing with environmental issues and Critical Zone research. Though the lower boundary for classifying soils is set at 200 cm in both Soil Taxonomy (ST) and the World Reference Base (WRB), these systems are ill equipped for categorising layers below diagnostic horizons. The authors reflect on the need for classifying the solum–subsolum continuum based on data of four soil profiles from Brazil. The solum was classified with ST, WRB and the Brazilian Classification, and the subsolum with the Saprolite-Regolith Taxonomy (SRT) and the Subsolum Reference Groups (SRG). Soil classification systems provide limited information on shallow soils but this can conveniently be complemented with subsolum classification. SRT differs from SRG as it focuses on deeper material and on geotechnical applications, whereas SRG focuses on layers directly under diagnostic horizons and on environmental applications. Both systems still need more field testing. SRT seems to require more specialist knowledge on lithology than SRG and being a hierarchical classification system is less flexible than the open, low hierarchical organised SRG classification. It is concluded that future soil classification systems need more integration of the concept of ‘whole regolith pedology.’