ABSTRACT
Soils of aridic, xeric, and ustic soil moisture regimes occupy 6.5 x 109 ha in Africa, Southwest Asia, Southeast Asia, and South America (Higgins et aI., 1981). Physical properties that are suggested to be common to many arid and semiarid region soils include high erodibility, high runoff generation potential, susceptibility to seal and crust formation, poor water-holding capacity, profile hardening, structural instability, low clay content, low activity clay, high bulk density, and high surface temperatures in the summer months (EI-Swaify et aI., 1984; Guthrie, 1982; Lal, 1985). It is necessary to be cautious in making generalizations about soils that occur throughout the world in a vast array of combinations of soil-forming factors. For example, most of the soils of the arid and semiarid parts of Chile seem to fit these characteristics (Vial and Wright, 1965), although Vial and Wright show that the soils have a wide range of textures and profile properties over the wide range of precipitation and elevations existing in Chile. Surface textures are often sandy, and subsoils have considerable silt and clay. Claridge and Campbell (1982) show that there are many similarities between hot and cold desert soils, including horizon development and the distribution and chemistry of salts. For the purpose of this review, cold arid regions, such as Antarctica, are not considered.
