An element is essential to plants if it is necessary for supporting its normal growth and reproduction. The requirement of this element rnust be specific and is not replaceable by any another element in the soil. They must be directly involved in the metabolism of the plant.
Criteria for Essentiality
An eleryent cannot be considered as essential merely on the basis of its presence in the plant. It is considered essential on the basis of the following criteria
(i) The plant is unable to grow normally and complete its life cycle in the absence of the element.
(ii) The element is specific and cannot he replaced by another element.
(iii) The element plays a direct role in the metabolism of the plants.
The essential element. are futher classified into two categories
(a) Macroelements These are the elements required by plants in larger quantities. These C, H, O, N, P, K, Mg, Ca and S.
(b) Microelements (Trace elements) These are required by plants in low quantities (Often less than 1 ppm). These include B, Zn, Mn, Cu, Mo, Cl, Fe and Ni.
