Extremely arid soils of the Ili Depression in Kazakhstan

On the basis of macro- and micromorphological and analytical studies of extremely arid soils of the Ili Depression in Kazakhstan, a comparative analysis of pedogenetic processes shaping these soils on piedmont plains of different ages and heights is performed. The types of soil horizons and their combinations are analyzed in the context opf modern Russian and international soil classification systems. The genesis of extremely arid soils is controlled by the climatic conditions and by their geomorphic position on alluvial fans of piedmont plains. The following processes are diagnosed in these soils: soil crusting with vesicular porosity, the development of desert pavements with rock varnish, rubification, surface salinization, and iron depletion around the pores. It is suggested that the initial factor-based name (extremely arid) of these soils can be replaced by the name vesicular-crusty soils with the corresponding AKL diagnostic horizon, which is more consistent with the principles of substantive-genetic classification systems. In order to determine the classification position of these soils in terms of the new Russian soil classification system, new diagnostic horizons—AKL and CS—have to be introduced in this system. According to the WRB classification, the studied soils belong to the group of Gypsisols; the soil with strong salinization fits the criteria of the group of Solonchaks. A qualifier [yermic] is to be added to reflect the development of desert pavement and vesicular layer under extreme arid conditions.