(a) Macro-nutrients : Macro-nutrients are generally present in plant tisssues in large amounts (in excess of 10 m mole kg-1 of dry matter).
The macro-nutrients include carbon, hydrogen and oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium.
Of these carbon, hydrogen and oxgyen are mainly obtained from C02 and HzO while the others are absorbed from the soil as mineral nutrients.
(b) Micronutrients : The elements needed in a very small amount (less than 10 m mole Kg-1 of dr) matter) are called micro-nutrients. These are alsc called as trace elements.
These include iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.
(c) Beneficial nutrients : The elements which are not essential for plants but their presence are beneficial for the growth and development. Such element are called beneficial elements,
(d) Toxic elements : .uneral ion concentration
in tissues ‘bit reduces rhe dry weight of tissues by about 10 percent is considered as toxic element. Toxicity levels for any elements also vary for different plants.
For example, the prominent symptom of manganese toxicity is the appearence of brown spots surrounded by chlorotic veins.
(e) Essential element: An essential element is the one which has a specific structural or physiological role and without which plants cannot complete their life cycle.
16 elements have been found to be essential. They are C, H, O, N, P, K, S, Mg, Ca, Fe, B, Mn, Cu, Zn, Mo, Cl