Because potassium is relatively immobile in the soil, it should be applied at seeding and incorporated into the soil. For established stands, apply K as a topdress treatment in the fall. Most soils in northern Idaho contain sufficient amounts of K for maximum plant growth and yields. Consequently K fertilizer will rarely be needed on fields in conservation programs in Idaho. Potassium fertilizer needs based on a soil test.
Sulfur is second only to N in importance for grass production.
Without adequate S, the grass will appear light green to yellowish-green in color. This is similar to the appearance of plants having a shortage of N. Plants require S to use N efficiently. Since the legumes in the mixture will symbiotically fix N for their own use as well as provide N for the use of the grasses in the mixture, the S fertility will be the most limiting factor. Since S is mobile in soils, it is subject to leaching. Consequently, soil should be tested for S every year, especially in areas of annual cropping and high precipitation.