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The chemistry of the elements is predominantly ionic, but a slight degree of covalent bonding occurs in bonds to oxygen, N and carbon in various chelate and organometallic compounds. The tendency to covalence is greatest with lithium (Li) and least with cesium (Cs), which is expected from their charge/radius ratios. The concentrations of sodium and potassium (K) can range up to several percentage points in soils while those of Li, rubidium, and Cs rarely exceed several hundred micrograms per gram. Methods to determine total K and the other alkali elements in soils use acids or a high temperature fusion to decompose the soil. The chapter presents two procedures for measurement of nonexchangeable K in soils: a boiling HNO₃ method; and a hydrogen‐saturated resin technique. Soil test extractants for K were developed to easily and rapidly measure K in soils and to estimate K availability.