Iron (Fe) is the fourth most abundant element in the earth’s crust. It is vital for important plant functions such as photosynthesis, DNA synthesis, protein formation, biological nitrogen fixation, and respiration. There are three main classes of iron fertilizers include inorganic iron compounds, synthetic iron chelates and natural iron complexes.
A general chlorosis of young trees is the most telling symptom of iron deficiency. At first the veins may remain green, but in most species in which the deficiency has been observed the veins also become chlorotic eventually. The deficiency is common in fruit trees. Where it is associated with high levels of calcium carbonate in the soil, it is called "lime-induced" chlorosis.