The availability of potassium for plant uptake is determined by several factors, including the concentration of potassium in soil solution, the amount of potassium that is associated with soil minerals in both an exchangeable and non-exchangeable form, and the rate at which the potassium associated with soil minerals is released into soil solution, as a result of plant uptake. An understanding of the potassium dynamics in soil is of significant importance as cotton’s potassium uptake peaks during the boll fill stage, and proper K supply is critical to maximize yield and fiber quality. The objective of this talk is to review the dynamics of soil potassium, particularly as it relates to clay mineralogy and implications for soil testing and fertilizer recommendations.