The study of how plants absorb and assimilate inorganic ions is called mineral nutrition. This area of research is central to modern agriculture and environmental protection. High agricultural yields depend strongly on fertilization with mineral elements. Mineral elements are acquired primarily in the form of organic ions, and they continually cycle through all organisms and their environment. Mineral elements enter the biosphere primarily through the root systems of plants, so in a sense plants act as the "miners" of the Earth's crust. The large surface area of roots and their ability to absorb inorganic ions at low concentrations in the soil solution make mineral absorption by plants a very effective process. After being absorbed by the roots, the mineral elements are translocated to the various parts of the plant where they are utilized in important biological functions. Other organisms, such as mycorrhizal fungi and nitrogen-fixing bacteria, often participate with roots in nutrient acquisition.
Only certain elements have been determined to be essential for plant growth. An essential element is defined as one that has a clear physiological role and whose absence prevents a plant from completing its life cycle. If plants are given these essential elements, as well as energy from sunlight, they can synthesize all the compounds they need for normal growth. The most essential Macronutrients are: Nitrogen, Potassium, Calcium, Magnesium, Phosphorus, Sulfur, and Silicon. The most essential Micronutrients are: Chlorine, Iron, Boron, Manganese, Sodium, Zinc, Copper, Nickel, and Molybdenum. Mineral essential elements are usually classified as macronutrients or micronutrients, according to their relative concentration in plant tissue.
In order to demonstrate that an element is essential requires that plants be grown under experimental conditions in which only the element under investigation is absent. Such conditions are extremely difficult to achieve with plants grown in a complex medium...