In order to complete the life cycle normally, the living organism requires a supply of a large number of
substances from outside. This is called nutrition. If the supply needed by the organism is both organic
and inorganic, the organism is called heterotrophic, but if the supply needed by the organism is that of
inorganic substances only, the organism is called autotrophic or self-feeding. All green plants synthesizing
their own organic requirements are autotrophic.
Under normal conditions of growth, all green plants are autotrophic and they require from outside
the supply of only inorganic substances. All the inorganic plant requirements are obtained directly or
indirectly from the soil. As the sources of these inorganic requirements are minerals, the elements are
known as mineral nutrients and the nutrition is called mineral nutrition.
Thus, plant growth and development can proceed only when the plants are applied with the
chemical elements referred to as Essential Elements. These nutrients are absorbed by plant roots from the
soil.
Chemical analysis of the plant ash (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 indispensable or necessary for
the normal growth and development of the plants and they are called Essential Elements. Rests of the
elements are called Non-essential elements.
It is now known that the following 15 elements are essential for the majority of the plants :
C, H, O, N, P, K, Ca, S, Mg, Fe, Zn, B, Cu, Mu, and Mo. Besides these, Al, Si, Cl, Na, Co, and Ga may be
essential for some plants.
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