The investigation of soil formation and evolution of losses derived soils in a climosequence, case study: eastern of Golestan province

A climatic gradient was selected in order to evaluate the effects of the climatic factors on soil genesis, evolution, physical and chemical properties of loess derived soils in eastern Golestan Province. This gradient includes udic, xeric and aridic moisture regimes and mesic and thermic temperature regimes. Seven soil profiles were located under pasture land use were studied. Results showed that Mollisols with argillic and calcic subsurface horizons were present in the region with udic moisture regime and mesic temperature regime, while in the regions with xeric moisture and thermic temperature regimes, Mollisols have only cambic horizon and Inceptisols have ochric epidedons and calcic and cambic subsurface horizons. Meanwhile Aridisols and Entisols were eventually formed in aridic moisture regime and thermic temperature regime and Entisols did not show any evolution. Micromorphological studies showed that with reduction of rainfall and increase in temperature, soil microstructure changed from angular blocky and sub-angular blocky with strong separation to massive and blocky microstructure with weakly separation. Moreover speckled b-fabric changed to crystallitic b-fabric followed by the decrease in rainfall. Soil physico-chemical properties showed significant differences in soil texture, amount and depth of lime leaching, the amount of organic matter, pH, electrical conductivity of saturated extract, and cation exchange capacity. In areas with higher rainfall, the clay content as the weathering product of the silt particles has increased.