Potassium occurs in soils always with a single positive charge K+. Potassium is very soluble in water as the chloride or sulphate.It can be in solution in the soil, but is also adsorbed by negatively charged surfaces of clays or organic matter.Soils with abundant clay or organic matter hold reserves of potassium , while sandy soils do not have this ability and are more prone to potassium deficiency.Isaan soils are predominantly sandy and predominantly potassium deficient.