There has been increased interest in understanding the variability one sees in soil test potassium (K) levels within a field. Of particular interest is why after 3 or 4 years the soil test K (STK) levels are less than or greater than expected based on prior STK levels and nutrient budgets for K additions (fertilizer and/or manure) and removals (crop removal of K). It must be remembered that K availability is assessed by chemical extractions (soil tests). And any soil test only measures a fraction of the K in soil, specifically soil solution K and exchangeable K. This paper will highlight factors that affect exchangeable K and subsequently STK levels.