Nutrients needed in small quantities but still very much needed. These can become toxic or deficient more easily than the macronutrients. Availability of micronutrients is dependent on soil pH. Chelated forms are the best.
Chelation: The word chelate (pronounced “key-late”) comes from the Greek word “Chele” which literally means “claw”. Many necessary trace metal nutrients get bound up in the soil and are unavailable to the plants. Bacteria and fungi are natural chelators, breaking bonds and releasing nutrients to the plant. There are other non-biological chelators that can be added to manures and fertilizers.
Zn2+ – Zinc is necessary for plant function, especially in plant reproduction. Residual effects of Zn can last for several years so broadcast applications are recommended for heavy application. Increase in soil temperature raises Zn availability.
Mn2+ – Manganese quickly reverts to unavailable forms shortly after application so soil banding or foliar applications are recommended.
Fe2+ and Fe3+ – Iron ion Iron (Fe) quickly reacts with other elements and can become unavailable for the plant. Again, OM and biological activity keep iron in a plant available form.
Cu2+ – High OM, soil pH, as well as excessive nitrogen (N) and phosphorus (P) applications can cause Cu deficiency. Soil applications of Cu can be effective for several years.
Cl– – The chloride ion is highly soluble and mobile in the soil solution. Coastal areas can see naturally high depositions (100 lbs/acre) of chloride due to wind-sea interactions. Because of its mobility, Cl– readily leaches and moves with groundwater flow. Accumulation of Cl– can occur in areas with restricted drainage, a shallow groundwater table, or as part of seasonal fluctuations.