Variation and Evolution in Soil Properties as Affected Topography and Ground Water Table in Dasht- E- Arjan area, Fars Province

Soil is one of the most important natural resources and perhaps is the most fundamental factor in formation of civilization. In addition to food supply، the soil will also provide other human necessities such as clothing، residence، bury wastes، wild life، recreation and etc. Climate plays a very important influence on enhancing and processes of soil formation، and in addition the climatic factors play a considerable influence on plant growth، production and land use. In each region، topographic factor also influence soil characteristics. Its influence on soil development and plant growth depend on its direction and elevation. In other to study the effects of topography and depth of ground water on soil genesis، Dasht-E-Arjan plain with xeric and mesic soil moisture and temperature regimes، were selected. Based on aerial photographs and also topographic maps، the location map of the study area was drawn. Then on two transversal sections، six profiles were dug. Among them four representative profiles were selected for detailed studies. The results of field studies and also profile description showed that Entisols and Inceptisols orders were developed on alluvial-colluvial fans، while on piedmont plains and lowlands only Inceptisols were formed. The physico-chemical characteristics of studied soils showed that، among the studied profiles، there are remarkable differences in soil texture، organic matter، saturation percentage، pH، EC، and CEC. The most important soil forming processes were accumulation of surface soil organic matter and also formation of Cambic and Calcic horizons. Because of extensive cultivation، the color and thickness requirements do not satisfy for the formation of MollicEpipedon، which show great future hazards for all Mollisols of the country. The XRD results of clay minerals showed more smectite mineral with respect to kaolinite، illite and chlorite minerals. This could be due to its higher content in parent materials and also transformation of illite to smectite due to more wetness of low lying physiographies.