Deficiencies in iron are common in plants. This leads to a reduction in chlorophyll, causing the crops to struggle, and the younger leaves to yellow or to develop chlorosis.
Boron is necessary for the development of shoots and roots, and is essential during the flowering and fruiting phases of crops.
Zinc is required for the production of important plant hormones (such as auxin.) A deficiency of zinc causes structural defects in leaves and other plant organs.
Molybdenum is involved in plant enzyme systems that control nitrogen metabolism.
Information from Yara.