micronutrient

Micronutrients for plants There are about eight nutrients essential to plant growth and health that are only needed in very small quantities. These are manganese, boron, copper, iron, chlorine, cobalt, molybdenum, and zinc. Though these are present in only small quantities, they are all necessary.
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Mi·cro·nu·tri·ent n. A substance, such as a vitamin or mineral, that is essential in minute amounts for the proper growth and metabolism of a living [more]Micronutrient - Community and Resources

Noun
1. a substance needed only in small amounts for normal body function (e.g., vitamins or minerals)
(hypernym) substance, matter

Any essential nutrient that is a mineral (especially a trace element) or a vitamin.

MICRONUTRIENTE