ABSTRACT
The rates and extent of both mineral weathering and organic matter addition (and therefore soil development) are interactive functions of time, climate, topography, biological action, and parent material (e. g., Jenny, 1941). Climate (specifically moisture and temperature fluxes) severely restricts pedogenesis in dry environments, and arid region soils are typically characterized as weakly developed. Temperature influences evaporation, biological growth and activities, the rates of chemical weathering reactions and, together with water and slope (topography), governs physical weathering processes. Water serves as the principal chemical reactant in weathering, as the vehicle for removing reaction products from the localized sites of weathering, and, in arid environments, as the single most important agent limiting biological growth and activity. In the absence of water, soil development cannot proceed, and hence, many chronologically old desert soils are pedogenically young. Mature soils developed on arid landscapes, conversely, indicate great age and/or geomorphic stability and may even reflect a period of more intense weathering and biological activity associated with an earlier 'climate.
