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Macronutrients : Thoseelements which are generally present in plant tissues in large amounts (inexcess of 10 mmole Kg-1 of dry matter) and are involved in the synthesisof organic molecules and development of osmotic potential are calledmacronutrients or macroelement, e.g. carbon, hydrogen, oxygen, nitrogen,sulphur, potassium, calcium and magnesium etc.
Micronutrients : Those elements which are requiredby plants in’very small amounts (less than 10 mmole Kg-1 of dry matter) are called micronutrients, e.g.iron, zinc, manganese, boron, copper, molybdenum, chlorine and nickel. Theseelements are mostly involved in the functioning of enzymes as cofactor or metalactivators.
Beneficial nutrients : Those elements which arerequired by higher plants along with the macro and micronutrients are calledbeneficial nutrients, e.g. cobalt, silicon, sodium and selenium.
Toxic elements : Any mineral element if suppliedto plant tissue in such concentration that it reduces the dry weight of tissuesby about 10 percent, is called toxic element. e.g. manganese toxicity leads tothe appearance of brown spots surrounded by chlorotic veins. Excess ofmanganese induces deficiency of iron, magnesium and calcium.
Essential elements : Any element required byliving organisms to ensure normal gfbwth, development, maintenance, metabolismand causes deficiency symptoms if not supplied to the plant from externalmedium is called essential element, e.g. C, H, O, N, P, K, S, Mg, Ca, Mn, Cu,Mo, Zn, B, Cl, etc. Potassium plays an important role in opening and closing ofstomata, protein synthesis etc. Magnesium is found in chlorophyll andphosphorus in ATP. Mg2+ is an activator for both ribulose bisphosphatecarboxylase-oxygenase and phosphsenol pyruvate carboxylase.Zn2+ is an activator of alcohol dehydrogenase andMo of nitrogenase during nitrogen metabolism.