The four most common elements found in the atmosphere and soil are carbon, hydrogen, oxygen, and nitrogen. All of these are required by plants. Essential mineral elements are required by plants for growth and reproduction. In some cases, there is a fine line between deficiency and toxcity from these elements. There may be a very narrow range of concentrations that is optimal for the plant.
Soils provide nutrients and mechanical support for plants.
Many minerals exist as ions attached to clay particles, which have a net negative charge. The ion exchange capacity of soil is an indication of the ability of that soil to exchange protons for other ions attached to the clay particles. Soil fertility is determined to a large extent on its ability to provide nutrients through ion exchange. Fertilizers are added to soil that is deficient in one or more nutrients. Liming lowers the pH of the soil.