Potassium for plants

Coroneos, C., Hinsinger, P. and Gilkes, R.J. 1996. Granite powder as a source of potassium for plants a glasshouse bioassay comparing two pasture species. Fertilizer Research 45 143-152. 

The main source of potassium is potash rock, a group of sedimentary substances often found in association with rock salt, gypsum, and dolomite. The term potash itself was derived originally from the pot ash formed when seawater was mixed with wood ashes and boiled. Because of the importance of potassium for plant growth, about 95 percent of the worlds potash is converted into fertilizer. 

This may be seen in genes related to potassium. For plants, potassium is the element of summer and of stress. When summer heat and droughts stress the plant, it needs extra potassium to balance the shifts in osmotic pressure. Plants that make extra chromosomes have more genetic space to evolve genes that move the potassium around. Extra DNA gives the plant a better ability to control its potassium and respond to its environment. 

Fine-grained micas are present in nearly all soils. Frequently, they are the most abundant component of the clay fraction. In many soils, micas are the principal source of native potassium for plants. On weathering, micas are altered to vermiculite and sometimes to smectitelike minerals and, as such, significantly increase the cation exchange capacity and affect the relative selectivity by soils for various exchangeable cations. 

There is very little written about feldspar minerals in soils literature generally, and in fact most papers that have appeared have been concerned with the alkali feldspars as sources of potassium for plant nutrition. A more detailed study of the reactivity of finely divided feldspar particles in the presence of neutral salt and acidic solutions was made by Nash and Marshall [1957]. They concluded that the apparent exchange capacity of the surface layers was a sensitive function of the ions concerned and that (under the conditions of their experiments, at least) any poorly organized surface layer is not more than a few unit cells in depth. 

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