The remaining elements – iron (Fe), Copper (Cu), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), chlorine (Cl), and nickel (Ni) – are referred to as micronutrients (or minor/trace elements). Deficiencies in these elements can limit crop growth under certain conditions.
Five of the elements typically occur in the soil as positively charged cations: iron (Fe3+), copper (Cuf2+), manganese (Mn2+), nickel (Ni2+) and zinc (Zn2+). Molybdenum (MoO42-) and chloride (Cl-) occur as anions typically occur as anions in the soil solution and can be prone to leaching in certain soil types. Boron occurs in the form of a balanced or neutral compound as H3BO3.