1, Almost all elements which are present in soil and which get solubilized enter the plants. Nearly 60 elements have been detected in plants. However, all of them are not essential. Many of them simply enter the plants because of the common pathway with the essential elements, lead, gold, selenium.
2. Some minerals are required in extremely small quantity of even less than 1 kg/g of dry matter. Such small quantities are often present in water as well as in commercially available salts. Therefore, exact physiological role and deficiency symptoms of some elements cannot be studied unless and until extra pure water and extra pure salts are not used in studies employing hydroponics. 3. Macronutrients. They are those essential elements which occur in easily detectable quantities of 1-10 mg/g of dry matter, C, H, O, N, P, K, S, Mg, and Ca. Micronutrients. Micronutrients are essential elements found in plants in small quantities of 0.1 mg or less/g of dry matter, Fe, Zn, Mn, B, Cu, Mo, CI, Ni. Beneficial Nutrients, Nonessential elements which are required in metabolic activities of some plants are called nonessential functional or beneficial elements, silicon in grasses, cobalt vanadium, and sodium. Toxic Elements. The elements which when present reduce growth of plants by 10% or more are known as toxic elements: lead, Aluminum. Most micronutrient also become toxic in higher concentration, Mn2. Essential Elements. They are elements which have specific structural or functional roles in plants and without which plants are unable to complete their life cycle. Their deficiency produces disorders which can be corrected only by their supply e.g. C, H, O, N, P, K, S, Mg, Ca, Fe, Zn, Mn, etc