Development of Soil Geomorphology as a Sub-discipline of Soil Science.
Robin N. Thwaites, School of Natural Resource Sciences, Queensland Univ of Technology, Gardens Point Campus, Brisbane, Queensland 4001, Australia
The development of soil geomorphology (or pedogeomorphology) has synthesised the knowledge and techniques of the two allied disciplines of pedology and geomorphology. Soil geomorphology relates the study of the genetic relationships between soil materials and landforms with commensurate relationship between soil processes and land-forming processes. William Morris Davis, one of the architects of elevating geomorphology to a science, originally defined it as ‘...a function of structure, process and stage [time].' An early champion of pedology, Hans Jenny, expressed soils as being ‘… a function of climate, organisms, parent material, relief and time'. It largely remained that way until the quantitative revolution of the 1960s along with the import accorded to the states of equilibria and the significant interest in systems theory. The redirection of geomorphology and pedology as applied sciences necessitated their redefinition and the opportunity for their integration. The early soil-formation models of Glinka (Russia), Marbut (USA), Shaw (USA) and Jenny (USA) all accentuated the modern influences of climate and the biosphere as fundamental to soils rather than the longer term effects from the lithosphere and geomorphic domains. By the end 1940s, Robinson stated, ‘the domain of pedology may come to engross a considerable amount of dynamic geology'. By then, Milne had already published his concept of the catena, which was a clear integration of geomorphology (‘dynamic geology') and pedology within the domain soil science. Palaeosols had been recognised since the 1930s but their importance for pedological and geomorphic studies was not recognised until the 1940s when they were deemed to ‘hold promise as a key to environmental conditions of past geologic ages.' It was not until the 1950s that the soil scientists embraced geomorphological principles and concepts into their thinking to any significant degree. For example, the pioneering field studies by Butler and others during the 1950s to 1970s from the CSIRO in Australia, and some British work in Africa in the 1950s and 1960s. Only more recently has there been a move to formally embrace pedology as a component within geomorphology, especially through the use of soil stratigraphic concepts. Much of the work in this context developed in the midwest USA from the 1950s onwards through several workers including pioneers such as Ruhe, as well as by Birkeland from the 1960s onwards in the southwest USA, although much groundwork was done by the USGS, Corps of Engineers, and the USDA-SCS. The ‘soil landscape' as a soil-geomorphological concept has proved to be both popular and rewarding for landscape analysis and interpretation and is the basis for soil mapping in the USA and much of the rest of the world. The more recent (1970s) soil landscape system concept can be construed as a dynamic 3-dimensional pedogeomorphic model in keeping with an ecological interpretation of soil science. Soil landscape mapping in some instances now includes more formalised soil geomorphological approaches, such as the soil materials mapping method in New South Wales, as does regolith-terrain mapping for understanding regolith pedogenesis, stratigraphic analysis of surficial materials, and interpreting deeply weathered or residual soils. The future for soil-geomorphological research lies in the application of catenary soil-landscape systems analysis as soil-landscape modelling for the prediction of unobserved soil/regolith properties from observed land-surface features and knowledge of land-surface processes. The major assumption is that soil and geomorphic patterns co-vary through soil-geomorphic processes. Such explicit, quantitative models are crucial to further our understanding of earth surface and sub-surface features and processes. This rigorous modelling of the soil-landscape draws strongly on the State Factorial approach to pedogenesis but the holistic systems approach revises this basis completely.