مطالعه اثر تراز آب زيرزميني و نوع كاربري بر منشاء و توزيع كاني هاي رسي در خاك هاي لسي جنوب غرب استان گلستان

Distribution and origin of clay minerals influenced by ground-water table and land use in south-west Golestan province

Inheritance, transformation and neoformation are the three main origins of clay minerals. Factors such as topography, parent material, ground water table, climate and land use change may affect their relative quantity and distribution pattern. This study was carried out in southwest Golestan in three different ground water table depths and forest, dry fanning and hydromorphic conditions. The main soil moisture and temperature regimes are xeric-thermic and udic-mesic and the parent material is loess. The results showed that illite, smectite and kaolinite minerals are the main minerals in all studied soils. In the forest land with good drainage, well-leaching and lower pH, chlorite has not been observed. In hydromorphic Soils with the near surface ground water and poor drainage, the amount of smectite minerals was maximum and its origin was mainly related to neoformation. In soil under dry farming and deep ground water, drainage is favorable and the leaching process have provided favorable condition for K+ release and transformation of illite into smectite. Decrease in amount of illite with depth is mainly due to its transformation to smectite and in soils with poor drainage and near surface ground water can be related to limitation of lessivage and physical weathering due to seasonal variation of temperature and moisture. Occurrence and stability of vermiculite in the forest land is due to high leaching, increasing A1 activity and relatively low pH of soil. Kaolinite has the inheritance origin and there is no clear relation between its quantity, ground water table and land use. Land use and ground water table depths are the most effective factors in distribution pattern and the relative amount of smectite and illite minerals. The distribution of vermiculite however is mainly affected by climate.