You have seen that cation exchange plays an important part in nutrient availability to plants. Cation exchange functions in two ways as nutrients are released for the use of plants and microorganisms. In one case, the nutrients freed by cation exchange find their way into the soil solution. There they may ultimately contact the absorptive surfaces of roots and soil organisms or they may be removed by drainage water. Second, if the contacts of root hairs and microorganisms with the soil colloidal surfaces are close enough, there may be a direct exchange of cations between the colloidal particles and the root hairs or microbes. Under such a condition, the hydrogen ions, generated at the surface of root hairs or microorganisms, are thought to exchange with the adsorbed cations on the colloidal micelle without any of these ions having first been released to the soil solution.