Potassium

The amount of potassium in a soil may be as much as 80,000 lb per acre, of which only 150 lb or 2 percent is available for plant growth. When solubilised, half will be held as exchangeable cations on clay while the other half is in the soil water solution. Potassium fixation occurs when soils dry and the potassium is bonded between layers of clay. Under certain conditions, dependent on the soil texture, intensity of drying, and initial amount of exchangeable potassium, the fixed percentage may be as much as 90 percent within ten minutes. Potassium may be leached from soils low in clay.