Relationship of Potassium Forms with Soil Physicochemical Properties and Clay Mineralogy in Ghrehbagh Plain, Fars Province

Different forms of potassium (K) in soils are closely related to clay minerals and soil physicochemical properties. The present research was conducted to investigate the relation between soil physicochemical and mineralogical properties with different forms of K in soils of Ghrehbagh plain, Fars Province. Eleven soil pedons with the maximum soil variation were selected. Clay mineralogy was determined for surface and subsurface horizons of each pedon, where physicochemical characteristics and different forms of K were analyzed for all horizons. Soluble, exchangeable, non-exchangeable, and structural K were among different forms of potassium studied. Entisols, Inceptisols, Mollisols, Alfisols, Histosols, and Aridisols were identified. Illite, kaolinite, vermiculite, chlorite, smectite and palygorskite were the dominant clay minerals investigated. Different forms of K (with the exception of soluble form) showed negative correlation with sand and calcium carbonate contents, but a positive correlation with clay and cation exchange capacity (CEC). In the studied area, the highest amount of soluble K (42.4 mg.kg-1) was observed in Histosols with a high percentage of organic carbon (18.7%). Results of the study showed that the lowest amounts of all different forms of K were found in Entisols with sandy loam texture and high CaCO3 content (87.5%). On the other hand, the highest amount of exchangeable (286.6 mg.kg-1), structural (6607.1 mg.kg-1), and total (7309.4) K were observed in Alfisols. In the studied area, maximum non-exchangeable K (505.7 mg.kg-1) was measured in Inceptisols with Vertic properties, high clay (40.6 %) and moderately low CaCO3 (37%) contents. Total K contents in Histosols were low, that is why the ratios of soluble, exchangeable, and non-exchangeable K contents to total K were the highest among other studied soils.