He explains that most soils already contain enough potassium to supply the needs of turfgrass. When this is the case, then simply applying the optimum amount of nitrogen will result in the grass obtaining all the potassium it needs from the soil. Dr. Rossi suggests that potassium fertilizer applications can be reduced (or eliminated) with no effect on turfgrass performance.
How can you tell if your soil has enough potassium? As a general rule, turfgrass soils with more than 50 ppm potassium as measured by the Mehlich 3 extractant do not require supplemental potassium fertilizer.