Micromorphology and clay mineralogy of loess-derived soils of natural and cultivated land uses along a climosequence in Golestan Province

To study the effects of land use change and climate on micromorphological properties and clay minerals distribution in loess derived soils of Golestan Province, 12 soil profiles in summit geomorphic position consisting of aridic, xeric and udic moisture regimes with cultivated, pasture and forest land uses were studied. The results showed that in aridic moisture regimes weakly developed Entisols, in the xeric soils moisture regime, Inceptisols, Mollisols were dominant, and in udic moisture regime, the most developed Hapludalfs were formed. Micromorphological studies revealed that there was a good positive correlation between soil development and climate index (evapotranspiration ratio). Environmental conditions such as land use and climate consequently affected micromorphological properties such as voids, microstructure, b- fabric, and pedofeatures. In the udic moisture regime, thick clay coatings were observed in speckled b- fabric matrix. However, in the soil with aridic moisture regimes, massive microstructure, and crystallitic b- fabric can be seen. Microscopic observations showed granular microstructure in forest surface horizons has been transformed to massive microstructure in cultivated land use. Results obtained from mineralogical studies showed that there were differences in type and distribution of clay minerals in different climate. Illite was found as the main clay mineral of loess parent materials and soils of the three land uses. The origin of illite, kaolinite and chlorite clay minerals are mainly inheritance while smectite and vermiculite are pedogenic. With increasing precipitation and weathering intensity from xeric zones toward udic zone, illite and chlorite have transformed to smectite and vermiculite. Amount of smectite and vermiculite are mainly affected by climate. It can be concluded that conversion of natural land resources into croplands causes serious soil degradation in loess derived soils in Golestan province.