Micronutrient

An element which is vital for plant growth in relatively small quantities. There are seven plant micronutrients: Boron, Chlorine, Copper, Iron, Manganese, Molybdenum, Zinc (and Nickel for some crops). Cobalt is often included as a micro-nutrient for legume crops. Another term used for a micronutrient is Minor Nutrient, or Trace Element.