Study of physico-chemical and mineralogical properties of gypsiferous soils in the north of Urmia

Gypsiferous soils comprise an important part of soil resources in arid and semiarid areas in the world and gypsum is the most common sulphate mineral in the soils of arid and semiarid areas. Accumulation of gypsum in the soils affect the most of physic-chemical, mineralogical and engineering properties of soils and in the most of cases results in serious problems for human activities. In this research, 9 soil profiles that all mostly located on the gypsiferous parent material in Nooshi Shahr region, were dug, described and sampled and their morphological, physical, chemical and mineralogical properties were determined using standard methods. Finally, soils were classified according to American soil taxonomy (2014). According to the results, gypsum content of soils varied from 62.91% in Cyy horizon of profile 1 to 2.91% in Ap horizon of profile 8 and each change in gypsum content of soils followed by variations in other properties of soils. Results showed that the soils with higher gypsum content had lighter color, lighter texture, lower values of organic Carbone and cation exchange capacity and higher values of electrical conductivity. These parameters reversely changed with decreasing of gypsum content of soils. Mineralogical studies revealed the presence of smectite, illite, chlorite, vermiculite and palygorskite as major clay minerals in these soils. The origin of illite, chlorite and kaolinite were related to the inheritance from parent material and the origin of vermiculite was related to the transformation of illite. Smectite group of clay minerals in these soils have been resulted from three origin of inheritance from parent material, transformation of other minerals (especially from illite) and neoformation. Palygorskite had pedogenic origin and has been formed in the soil via neoformation. The comparison of clay mineralogy of soils with different gypsum values revealed the presence of higher smectites in soils with higher gypsum and palygorskite was identified just in soils with higher gypsum. But, in soils with lower values of gypsum, illite and chlorite were the predominant clay minerals and palygorskite has not been identified in these group of soils. Finally, regarding to the effect of gypsum on morphological, physical, chemical and mineralogical properties of studied soils, in order to optimum use of these soils, revision in their management is necessary.