Potassium is an alkali metal even more reactive than sodium, soft enough to be cut with a knife; the metal itself is almost never used directly in daily life, and its value lies almost entirely in its compounds and in agricultural potash. In the laboratory, metallic potassium is a strong reducing agent and drying agent, often used to dry certain inert organic solvents, and to prepare sodium-potassium alloy—a liquid at room temperature with good thermal conductivity, once used as a heat-transfer medium in nuclear reactors and some high-speed centrifugal equipment. In optoelectronics and specialty lamps, potassium-rubidium lamps and potassium discharge lamps are used in certain spectral analyses and precision optical instruments. Far more importantly, potassium is one of the three essential macronutrients for plants, and the great majority of the world's potassium resources enter agriculture as potash fertilizer, supporting high and stable yields of grain crops. Because potassium metal reacts violently with water, is flammable and explosive, and is extremely dangerous to store and transport, it is never stockpiled in bulk by industry; when needed it is often produced on the spot or handled in small quantities under strict protection.
Potassium chloride (KCl) is the principal potash fertilizer, applied directly to fields to supplement potassium and promote sturdy crop stalks and resistance to disease and lodging; it is also the raw material for other potassium salts and potassium hydroxide. Potassium hydroxide (KOH), commonly called caustic potash, is strongly alkaline and is used to produce potassium-based soaps, alkaline-battery electrolytes and leather processing, as well as in cosmetics. Potassium nitrate (KNO3) is both a strong oxidizer—historically one of the three ingredients of black powder—and is now used in matches, fireworks, metal heat treatment and meat curing, as well as a nitrogen-and-potassium source in soilless cultivation and agricultural fertilizers. Potassium carbonate (K2CO3), commonly called potash, is used as a flux in glass and enamel, in soap making, textile printing and food acidity adjustment, and is also the raw material for potash glass. Global potash resources are highly concentrated in soluble potash deposits in Canada, Russia and Belarus; once mined, they are sold worldwide mainly as potassium chloride, making potash one of the three major agricultural mineral fertilizers, alongside nitrogen and phosphate fertilizers.
