Potassium is abundant in nature, comprising about 2.4 percent of the earth’s crust. The potassium content of soils varies widely, ranging from only a few hundred pounds per acre (furrow-slice 6" depth) to over 50,000 pounds per acre or more in fine-texture soils formed from rocks that are high in potassium-bearing minerals. All naturally occurring potassium contained in the soil originated from the disintegration and decomposition of potash-feldspars (orthoclase and microcline) and micas (muscovite and biotite). Much of the natural potassium occurring in soils is not available to plants and crops; therefore, soils containing relatively large amounts of total potassium usually respond to potassium fertilization.