Friday, 14 July 2006

Global Distribution of World Reference Base Soils in Relation to Key Soil Forming Factors.

Jonathan M. Gray, NSW Department of Natural Resources, 10 Valentine Ave, Parramatta NSW 2150, Australia, Geoff S. Humphreys, Department of Physical Geography, Macquarie University, Sydney, NSW 2109, Australia, and Jozef Deckers, Catholic University of Leuven, Vital Decosterstraat 102, 3000 Leuven, Belgium.

The relationships between World Reference Base (WRB) soil distribution and the key soil forming factors of parent material, climate and topography are examined at the global level using the ISRIC WISE Global soil dataset. The WISE Global soil dataset, established by ISRIC, contains 4382 geo-referenced soil profiles from 123 countries. The dataset was queried to derive the FAO 1988 soil types and qualifiers in each of 70 different environmental regimes, being combinations of different parent material, climate and topography. The outputs were then re-expressed into WRB equivalents. Only 1670 profiles matched the query requirements, meaning several environmental regimes were represented only poorly or not at all. The results were presented in a matrix of pie charts showing the relative proportions of WRB soil types and qualifiers in each environmental regime. Finally, the results were synthesized into two diagrams, presenting overall patterns of WRB soil distribution in relation to the key variables (see draft Figures 1 and 2). The examination of the dataset has revealed clear trends in the global distribution of WRB soil types. The results provide a basis for the prediction and modelling of WRB soil types expected under different environmental regimes around the globe. For example, it is demonstrated that sites with arid/humid climates - near level terrain mafic/intermediate parent materials are dominated by Vertisols and Luvisols, and that most wet sites are dominated by Acrisols and Ferralsols. Further statistical examination of various specific soil properties (pH, CEC, clay content, etc) under different environmental conditions using this and other major soil datasets has also been undertaken by the authors and presented in a companion paper at this Conference.

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