The rate of potassium (K) release from soils can significantly influence K fertility of soils. The aim of this study was to assess the impact of different land uses on K release from calcareous soils, within agricultural areas of western Iran. The kinetics of K release in 0.01MCaCl2 was studied in surface samples of 62 calcareous soils planted to pasture, orchard, garlic, leafy vegetables, wheat, and potato. Trend in K release kinetics was similar between land use types. We found that samples collected from pasture gave the lowest K release (245.2mg kg-1), whereas the highest values were measured on samples from leafy vegetables (449.6mg kg-1). Different models were used to describe K release. In general, Elovich, parabolic diffusion and power equation were found to be appropriate for modeling K release. The K release rate for the soils was estimated by parabolic equation and it was significantly different between land use types. The release rate was lower for pasture and wheat (averaged 16.1 and 25.1mg kg-1 min-1/2, respectively) than leafy vegetables (27.4mg kg-1 min-1/2) and potato (27.0mg kg-1 min-1/2). When the rate of K released found from parabolic model regressed on K forms and soil properties, NH4OAc-K, CaCl2-K, pH, and EC appeared to be the most important K forms and soil properties influencing K release rates in these calcareous soils. The different K release and NH4OAc-K or CaCl2-K prior to K application both should be taken into account for potassium fertilizer application in different land uses.
