Classification and Essentiality of Mineral Elements

Classification of minerals : Minerals were traditionally classified, on the basis of whether the plant absolutely required them, into essential and non-essential elements. Essential minerals -- such as C, H, O, N and P -- are indispensable: without them a plant cannot complete its life cycle, and their absence produces clear deficiency symptoms, because they play direct structural and physiological roles. Non-essential elements, by contrast, are not indispensable and their absence does not produce deficiency symptoms. This classification is obsolete now.

Based on the quantity requirement, minerals are also classified as minor or microelements and major or macroelements - a classification that divides minerals by the quantity in which the plant requires them. Microelements (or trace elements) -- such as Zn, Cu, Mn, B, Mo and Cl -- are needed only in minute amounts, mainly because they act as catalytic co-factors for enzymes. Macroelements -- such as C, H, O, N, P, K, S, Ca, Mg and Fe -- are needed in much larger quantity and mainly play nutritive and structural roles (C, H and O being the non-mineral major elements among them). This classification is not accepted now either.