The present research was conducted to study K forms and fixation in soils of southern Iran (Hormozgan Province) with aridic and aridic-ustic regimes and to address the relations between soil mineralogy and potassium forms. Thirteen surface soil samples (0-25 cm) were collected from different regions and analyzed in laboratory. Illite and feldspar and mica are the major clay and soil minerals for K reservoir, respectively. Mean of non-exchangeable, exchangeable and total content of K were equal to 31.3, 283.9 and 1080.6 mg kg-1 soils, respectively. These forms of K were abundant in plateau and piedmont plain physiographical unites while the greatest amount of soluble potassium was observed in flood and alluvial plain units. Despite the aridity of the region with low clay fraction and unlike the previous studies in calcareous arid soils of Iran, the amount of potassium fixation in soils was high, probably due to the predominance of micaceous minerals. In an adsorption experiment, the average K adsorption in soils was 71 percent after adding 1000 mg K kg-1. In general, the most active component in the K fixation was the silt fraction, dominated mica and illite. Potassium fixation boosted after increasing the wetting and drying cycles in relation to the samples that did not suffer these cycles.
