The nature of soil potassium can be summarized by Figure 6.4. Available soil potassium is found associated with the clay complex and soil solution. It is in equilibrium with the slowly available minerals, which are constantly supplying available potassium. Potassium is added by fertilizers and crop residues. Fertilizer potassium may be fixed and become slowly available; it may be lost by crop removal, leaching and erosion.

Figure 6.4. Available potassium in relation to additions and losses.