Thus, colloids can be viewed as huge anions surrounded by a swarm of rather loosely held cations. The amount of water associated with a particular cation is important, because the effective radius of the cation changes with the amount of hydration, or associated water. Many of the other plant nutrient cations are found only in very small amounts as cations on colloidal surfaces. More often, they are found as chelates or in chemical combination. Instead, they exist as free anions in the soil solution or fixed within chemical compounds.
Cation exchange is a phenomena which is constantly going in soils and is of great importance.
Without some mechanism to temporarily hold cations in the soil, plants would be unable to obtain sufficient quantities of the essential nutrients to grow. Without cation exchange, the nutrients would simply be leached downward in the soil and lost. Cation exchange plays a role in other soil processes as well. If cationic fertilizer nutrients are not held by the soil colloids, the nutrients would be lost to percolation water. Cation exchange between soil colloids and the soil solution.