The comparison of CaCl2 and organic acid ability in kinetics of non-exchangeable potassium release in dominant soils series in Golestan province

The release rate of non-exchangeable K (NEK) plays a significant role in supplying necessary K for plants, particularly in soils containing K bearing minerals. Information about NEK release rate in Golestan soils is limited. Kinetics of non-exchangeable potassium release, therefore is necessary in management and optimum use of soil resources. Laboratory experiment was conducted on NEK release of saturated soil sample by calcium from 2 to 1844 (h) duration in 12 dominant soil series of Golestan province. Different soils indicated various responses in successive extractions. The rate of K released was lower in CaCl2 than organic acid. The mean of the potassium release by oxalic acid was 2.33 times higher than potassium release by CaCl2. K release was faster in earlier periods in all soils followed with a lower release rate. The Elovich and Parabolic diffusion equations described well the NEK release kinetics by organic acid and power, first order and Elovich equations were suitable to describe the NEK release kinetics for CaCl2, based on their highest coefficient of determination, and their lowest value of the standard error of the estimate. Therefore, NEK release kinetics of soils were found to be influenced by diffusion, indicating that NEK release rate was controlled by K diffusion out of the mineral interlayer.