Clay Minerals Identification of Different Soil Orders in Northern Iraq

• Nidar Samarkhan Abdullah1 Mohammed A. Fayyadh2

  Author

One of the main criteria for determining soil formation and its features is mineralogical composition of clay components. However, the relationships among clay minerals, soil orders, and soil profile development in the calcareous soils of the semi-arid regions of northern Iraq have not been thoroughly investigated. In this study, the analysis of clay mineral types in Vertisols, Mollisols, and Aridisols is conducted using X-ray diffraction. Additionally, physicochemical characteristics of soil are estimated. A series of 30 soil samples was selected at two depths (0-30 cm and 30-60 cm) and analyzed for clay mineral content, cation exchange capacity, carbonate concentration, organic matter, and exchangeable nutrients. Clay minerals found in the analyzed soils include illite (100%), kaolinite (100%), palygorskite (96.6%), vermiculite (93.3%), chlorite (83.3%), and smectite/montmorillonite (53.3%). The predominant clay mineral in Vertisols is smectite (montmorillonite) with the largest cation exchange capacity (29.20 cmolc/kg). Illite, kaolinite, vermiculite, and the occurrence of palygorskite in the studied soil orders may reflect the effect of parent material composition, carbonate-rich conditions, and high evaporation or alkalinity. It may also be a neoformation or inherited material from the soil solution, whereas smectite (montmorillonite) was largely restricted to the Vertisols and, to a lesser extent, the Aridisols. Statistical analysis showed that soil orders are more influential for mineralogical differences than soil depth. The cation exchange capacity of the soils was more closely associated with clay mineral assemblages than with carbonate content alone. It is concluded that inheritance from parent materials and carbonate-induced pedogenesis are the key factors determining clay mineral associations and soil functions in the study area.

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