Micromorphology of Argillic Horizon Developed on Loess Derived Soils in Humid and Sub Humid Regions of South Western Golestan Province

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Development of argillic horizon in loess derived soils under Xeric and Udic soil moisture regimes was studied in Golestan Province. Soils were classified as Hapludalfs and Haploxeralfs. High leaching, stability of the surface, forest vegetation,structure and well drainage conditions provide appropriate conditions for clay migration through the profile and formation of argillic horizons. In the studied soils, the main observed pedofeatures were clay coatings and decalcified zones. Clay coatings were observed mainly in soils with crystallitic-speckled and speckled b-fabric, with smectite and vermiculite as dominant clay minerals. Laminated and thick clay coatings were seen in vermiculitic soils along with calcite infillings, hypocoatings and dominantly decalcified zones. Type of clay minerals, shrink/swell properties, and level of precipitation are factors affecting the abundance of clay coatings. In the well-developed horizons, the occurrence of vermiculite clay mineral has reduced the shrink/swell potential and increased the amount of clay coatings. A high carbonate content (CaCO3) in the lower horizons was the result of re-calcification processes. This hypothesis is supported by the more extensive amounts of CaCO3 in lower horizons than in the upper horizons as well as calcite coatings along the channels and voids. Parameter analysis through MISECA development index showed that clay coatings and calcite depletion pedofeatures were the major factors of MISECA index for the development of argillic horizons. Moreover, results showed that, in addition to the climate factor, extent and kind of clay minerals affected the development of the argillic horizons.

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