Potassium is a primary turfgrass nutrient and is usually supplied annually as fertilizer to lawns. It makes up about 1.0–2.5 percent of the plant’s dry weight, and its primary role involves regulating several important physiological processes. Potassium activates plant enzymes used in protein, sugar, and starch synthesis. It also plays a key role in maintaining turgor pressure in plants. Thus, it has a strong influence on drought tolerance, cold hardiness, and disease resistance of turfgrasses. Deficiencies of potassium in turf may be expressed as increased susceptibility to drought, winter injury, and disease.
Although large quantities of potassium are present in soils, only a small fraction is available to plants. Most soil potassium is in unavailable forms as feldspar, muscovite, and biotite minerals. Potassium is available to turfgrasses in the ionic form (K + ) and occurs in the soil solution and on negatively charged soil particles. In general, more plant-available potassium is present in fine-textured mineral soils (soils that contain high amounts of clay) than in sandy soils, especially in areas that receive high amounts of rainfall or are regularly irrigated. The best way to determine potassium needs for turfgrass is through soil testing.
Potassium is mobile in plants and sometimes can be taken up in amounts greater than needed for optimum growth. This phenomenon, called “luxury consumption,” is generally considered inefficient use of the nutrient. It is difficult to determine if luxury consumption is a problem in turf culture since very little information is available on the optimum concentrations of potassium in turfgrasses.
Potassium can be supplied to turf using inorganic fertilizers, natural organic fertilizers, or both. However, most fertilizer potassium is derived from inorganic sources, in particular, muriate of potash (potassium chloride) and sulfate of potash (potassium sulfate). Both of these fertilizers are water soluble.