ИСТИНА

The pedogeography of arid lands differs from that developed for humid areas both in global scale and in the internal organization of soilscapes. This work summarizes the experience of the author in the observation of soils of arid regions of the world. The examples are taken from such areas as Northern and Central Mexico, Uzbekistan, Sakha Republic (Russia), Namibia, and some others. Some of the regions have been studied in detail, and the others received less attention during short travels. The common pedogeographical features of all the arid regions were the following: 1)The soils of arid lands are commonly similar all over the globe. However, there are regional differences: extra-arid lands commonly have soils with evident accumulations of gypsum and soluble salts, which are uncommon in less arid climates. The regions with close permafrost have soils with cryoturbations and other cryogenic features. 2)Permafrost, on the one hand, favors the development of vegetation, including the arboreal vegetation, in the dry area, by preventing water percolation outside the profile, and by providing additional moisture by permafrost melting. On the other hand, the biological activity of cold arid soils is low due to extremely cold conditions. 3)Most of the arid regions are believed to be the zones of incipient soil formation. Poor development of soil profiles should be ascribed both to low pedogenetic potential of arid regions and to the high rate of erosion-sedimentation in the absence of dense vegetation. 4)The processes of erosion and material accumulation have major effect on the organization of the soilscapes. In most cases the slopes of the mountains and hills are strongly affected by erosional processes, while the valleys receive sediments accumulated by water and wind. 5)The accumulation of sediments in the valleys is due to the aeolian activity, alluvial sedimentation and irrigation. The accumulation rate is irregular, and thus the sediments have distinct layered structure. 6)In a regional scale, the distribution of soils depends on the geochemical fluxes in a landscape. Longtime development of a landscape results in the formation of gypsum, calcium carbonate, and silica- cemented hardpans in accumulative positions. 7)The catenary structure of arid soilscapes is determined both by the geochemical links and to the erosional redistribution of sediments along a slope. The “steady state” models for soil catenas are not suitable in arid regions. 8)For many soils the distribution of carbonates, gypsum and salts play a crucial role in their profile development. The distribution of the components mentioned above depends on the pedogeographic scale laws: their downward and upward movement is different in large and small topographic elements. 9)Most arid soils and soilscapes preserve features developed in ancient, in places much more humid epochs. In places these relict features completely determine the structure of an actual soilscape.