Essential Plant Nutrients

What is an Essential Element?

The number of elements considered essential for the growth of higher plants now varies from 16 to 20 or more, depending upon the definition of essentiality. The authors of this book are aware that Arnon* limits essentiality to only those elements that are needed for higher plants to complete all life functions and that the deficiency can be corrected by the application only of this specific element causing the deficiency. Other scientists such as Nicholas believe that an element should be considered essential if its addition enhances plant growth even though it merely substitutes for one of the 16 elements that Arnon declares to be essential. For example, because sodium can substitute in plant nutrition for some potassium, and vanadium for some molybdenum, Nicholas would consider both sodium and vanadium as essential, but Arnon would not. On the basis of the criteria used, Arnon specifies 16 elements and Nicholas 20 elements as being essential for the growth of higher plants such as cotton and corn. Three other debated nutrients are nickel (urea transformations), cobalt (N2 fixation), and silicon. (See Chapter 8 for further information on essential elements for plants.)

D. I. Arnon, "Mineral Nutrition of Plants," Annual Review of Biochemistry, 12 (1943), pp. 493 528.
D. J. D. Nicholas, "Minor Mineral Elements," Annual Review of Plant Physiology, 12 (1961), pp. 63 90

Criteria of Essentiality

Arnon (1954)

Plant cannot complete a function and cannot complete its life cycle

A deficiency can be corrected only by application of the specific element that is deficient

The element plays a direct role in metabolism

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