Release Kinetics of Non-exchangeable Potassium using CaCl2 in Relation to some Properties of Soils of Kohgilouye Province

Degree of soil evolution, type and amount of clay minerals are among the factors affecting potassium release from the soils. The release rate of non-exchangeable K (NEK) plays a significant role in supplying K for plants; particularly in soils that they are rich in K bearing minerals such as mica and feldespar. Kinetics of K release was studied by extraction with 0.01 M CaCl2 in 14 surface soils of different climatic regions of Kohgilouye and Boyerahmad Province, southwestern Iran. Mineralogical analyses revealed that smectite, illite, chlorite and palygroskite are major clay minerals of the soils studied. The release rate of NEK at the end of extraction (656h) was in the range of 38.1 (Typic Xerorthents) to 320 mgkg-1 (Calcic Haploxeralfs). In addition, the release rate of K showed higher correlation with the properties such as clay content, non-exchangeable K , CEC as well as illite and smectite contents. The amount of K release was in the sequence: Alfisols (222.3 mgkg-1) > Inceptisols (111.3 mgkg-1) > Entisols (105.0 mgkg-1). Power function, first order and parabulic diffusion equations could reasonably describe the K release kinetics. Fit of the data to these equations indicated that release of K is controlled mainly by diffusion process.