Factors affecting potassium pools distribution in some calcareous soils of Kohgilouye and Boyerahmad province

Different factors may affect potassium (K) content in calcareous soils. Potassium forms distribution as a function of various soil physicochemical properties was examined on seventy surface (0-20 cm) and subsurface (20-40 cm) soil samples of Kohgilouye and Boyerahmad province, southwest of Iran. Soil physical, chemical and mineralogical properties were determined according to standard methods. The soil was classified in Xeric and Ustic moisture regimes and Mexic, Termic, and Hyperthermic thermal regimes. As the result, the common clay minerals associations were found to be illite, smectite, chlorite and palygorskite with less content of vermiculite, kaolinite and quartz. Smectite, illite, and palygorskite were the main clay minerals occurring in humid and arid regions respectively. Soil soluble, exchangeable, non-exchangeable and structural K concentrations ranged from 1.2-12.1, 111-521, 153-1705 and 4584-10379 mg kg-1 at the surface and 0.2-5.0, 25-403, 72-1016 and 3227-9541 mg kg-1 at the subsurface soil samples respectively. Exchangeable, non-exchangeable, structural and total K concentrations positively correlated with soil clay content and cation exchange capacity (CEC), however negatively significant correlation was obtained with calcium carbonate content. Different forms of K (except soluble K) had positive and significant relationships with each other (r of 0.48-0.99) and this indicated the equilibration among K forms. Mineralogical studies indicated the positively influence of clay minerals, especially illite and smectite, on exchangeable and nonexchangeable soil K. While the structural and total K contents most affected by smectite and illitic clay minerals. Future studies are required about the mineralogy of soil sand and silt fractions and their influence on soil K status.