The definition of an essential mineral element (or mineral nutrient) was proposed by Arnon and Stout in 1939. They concluded that three criteria must be met for an element to be considered essential.
These criteria are:
- 1. A plant must be unable to complete its life cycle in the absence of the mineral element.
- 2. The function of the element must not be replaceable by another mineral element.
- 3. The element must be directly involved in plant metabolism.
These criteria are important guidelines for plant nutrition but exclude beneficial mineral elements.