Potassium Pools Distribution in Some Calcareous Soils as Affected by Climatic Conditions, Physiographic Units, and Some Physicochemical Properties in Fars Province, Southern Iran.

Experiments were conducted for thirty representative surface and subsurface soils collected from different physiographic units and moisture regimes in southern Iran to assess factors affecting K pools distribution and potassium release rate, using two organic and inorganic extractants and their association to mineralogy and some physical and chemical properties in calcareous soils. Mineralogical analysis indicated that illite, smectite, chlorite and palygorskite were the main clay minerals in the studied soils. The highest content of illite and smectite was observed in the piedmont plain (P.P) units, whereas that of smectite in Lowland (L.L) unit was higher than in soils of alluvial fans (A.F). It seems that the P.P unit which is in more stable landform position contains larger amounts of all K compounds due to higher clay and illite contents. The exchangeable, non-exchangeable (NEK), structural, and total potassium were found to be significantly and positively correlated to the clay content, cation exchange capacity, and the contents of illite, smectite, and vermiculite minerals, while a negative correlation as observed between the mentioned K forms and the calcium carbonate (CaCO3) content. The cumulative rate of K release to 0.01 M CaCl2 and oxalic acid was examined for a period of 1200 h, ranging within 104–286 and 87–233 mg kg–1 for the surface soil and 98–241 and 82–211 mg kg–1 for the subsurface soil samples, respectively. The percentage of non-exchangeable K released varied greatly between the different units and moisture regimes. Higher values of NEK release were observed for P.P followed by A.F, and L.L units. Considering the obtained values of the highest amount of potassium compounds as well as the release values in the piedmont plain physiographic unit and the xeric moisture regime as well as the Alfisols, the results confirm that in addition to physicochemical and mineralogical properties, physiographic units and soil moisture regimes also play a key role in nature and in spatial distribution of different forms of potassium. [ABSTRACT FROM AUTHOR]