THE CLASSIFICATION OF ARID ZONE SOILS

Soils in regions of arid and semi-arid climates exhibit only limited pedogenetic profile development, and they might be more usefully described, classified and mapped in terms of their depositional character. The main source of understanding of their origins and practical significance is likely to be the sedimentary geomorphology of the area concerned, rather than the minimal pedogenetic features. The term ‘sedosols’ is proposed for these soils and a method of classification is outlined, based on depositional features and origins. Sub-orders are based on mode of deposition to give four sedimentary families, viz. fluvial, littoral, aeolian, and anthropic. In lower category classification, series based on pedogenetic features cannot be defined and are replaced by the ‘depositional series’ characterized by the types of sediment (e.g. coarse textured, fine textured; saline, non-saline). Typical phases are based on soil depth and degree of erosion. Salinity induced by irrigation is also best recognized at phase level as it is essentially an ephemeral feature. The three major differentiating characteristics of sedosols are soil texture, degree of depositional stratification and effective soil depth.