Identifying the Possible Control of Clay Mineralogy of Soils in Some Southern US States over the Fluctuations in Potassium Fixation.

Soil potassium (K) exists in solution, exchangeable, and non-exchangeable forms that are in dynamic equilibrium with each other. The majority of total K budget in soils is controlled by primary K-bearing silicates such as illite and other mica, interstratified illite-smectite, and K-feldspars. The extent to which K is fixed in the phyllosilicates capable to host it (illite, I-S, smectite) depends on the exact type of clay mineral, its cation-exchange capacity, mineral charge density, the degree of interlayering, the moisture content, the concentration of K⁺ ions, the concentration of competing interlayer cations, and the pH of the ambient solution. A study was conducted using the incubation method to determine the potential for K fixation in representative soils in some selected Southern US States. The results demonstrated a 30-60% potential K fixation by the soils across the different locations. Soils in the study area have pH in the slightly acidic to slightly alkaline region. A preliminary XRD analysis of the bulk soil sample showed the presence of illite-like phases and feldspars, with the possible presence of some minor illite-smectite and kaolinite. A separation of clay fraction is to be conducted to determine its mineralogical content. Clay minerals that dominantly control the K content in analyzed soils will be identified, which will ultimately lead to the understanding of the role of decisive parameters responsible for K-fixation in soils (exchange reactions, availability under various dry-wet cycle situations, time, and temperature).