1. Livestock effluent, crop residue and other organic by-products from human activities are an important resource for fertilization.
2. Potassium is extracted from mines mainly as a mixture of sodium, potassium and sometimes magnesium salts. It undergoes purification to be transformed into potassium fertilizer usable in agriculture.
3. Potassium evolves in the soil in its mineral form as cation K+ . It may be bound in the crystal structure of the soil, adsorbed at the surface of clay minerals and also dissolved in soil water.
4. The leaching of dissolved potassium is a more pronounced in sandy soils with low cation exchange capacity (CEC).
5. Runoff and erosion (potassium bound to solid particles) are other mechanisms that remove potassium from agricultural plots.
6. Root absorption of plants is exclusively from potassium K+ dissolved in the soil solution.
Potassium deficiency primarily concerns the older leaves; it is characterised by a yellowing, then browning and desiccation of the limb and finally the edges of the leaf.
Too much potassium can affect the quality of production (less extractable sugar in sugar beets or less dry matter in potatoes). Excess potassium can also reduce magnesium absorption. Excess potassium can also interfere with the absorption of iron and manganese if these elements are not readily available.
The total potassium present in the soil is often derived from magma (mica, potassium feldspar), but is blocked in core particles from the original bedrock. Such geological potassium is altered and released, but that takes place over a long period of time and is insufficient in view of crop needs.
Sources of water-soluble potassium that can be used for fertilisation are rarer and are mainly located in in Eastern Europe and North America. These deposits come from old salt and sea beds where the water has evaporated, and which were then covered by other sediments and protected from erosion. These mines mainly contain sylvanite, which is a mixture of different water-soluble salts such as potassium chloride, sodium chloride and magnesium salts, and which are sorted and purified using physical separation processes.
Potassium interferes with magnesium. The order of priority for binding the ions to the clay complex is Ca>Mg>K>Na.