The below mentioned article provides a study-note on the essential and non-essential elements in plants.
Chemical analysis of the plant ash (i.e. the residue left after the dry matter of the plant has been burnt) has shown that plants contain about 40 different elements. Some of them are indispensible or necessary for the normal growth and development of the plants and are called as essential elements. Rests of the elements are called as non-essential elements.
According to Epstein (1972), there are two main criteria to judge essentiality of an element for plant:
(i) “An element is essential if the plant cannot complete its life cycle (i.e., form viable seeds) in the absence of that element” and
(ii) “An element is essential if it forms part of any molecule or constituent of the plant that is itself essential for the plant” (for instance N in proteins and Mg in chlorophylls).
It is now known that the following 17 elements are essential for majority of the plants:
C, H, O, N, P, K, Ca, S, Mg, Fe, Mn, Zn, B, Cu, Ni, CI and Mo (molybdenum.) Besides these, Al, Si, Se, Na, Co, V (vanadium) and Ga (gallium) may be essential for some plants.
Essential elements may be classified into two groups:
(1) Major Elements (Macronutrients):
The essential elements which are required by the plants in comparatively large amounts (1000 mg or more/kg of dry matter) are called as major elements or macronutrients. They are:-
C, H, O, N, P, K, Ca, S, Mg.
(2) Minor Elements (Or Micronutrients or Trace Elements):
The essential elements which are required in very small amounts (less than 100 mg/kg of dry matter) or traces by the plants are called as minor elements or micronutrients or trace elements. They are:-
Fe, Mn, Zn, B, Cu, Ni, CI and Mo.
(Trace elements should not be confused with the tracer elements. Tracer elements are usually radioactive or heavy isotopes which are used to trace out some metabolic pathway. Some examples of commonly used tracer elements in plant physiology are 14C, 15N, 18O, 32P, 35S, 42K and 45Ca.