Iron nutrition of plants in calcareous soils

This chapter reviews iron nutrition of plants in calcareous soils. Many agricultural crops worldwide, especially in semiarid climates, suffer from iron deficiencies. Deficiencies are usually recognized by chlorotic, or yellowed, intervein areas in new leaves and are typically found among sensitive crops grown in calcareous soils. Iron deficiency in extreme cases may lead to complete crop failure. Two principal methods of treating iron deficiencies are accepted. Spraying foliage with inorganic salts has been shown to be of benefit, but often gives spotty results because of, limited penetration of iron into leaves. Also, repeated treatments are required during the course of canopy development. Soil treatment with synthetic chelates, principally FeEDDHA (ethylenediaminedi–o–hydroxyphenylacetic acid), has been found to be an unqualified success, but for the drawback of their high costs. Iron deficiency in plants causes chlorosis of leaf tissue because of inadequate chlorophyll synthesis. In a healthy plant, 60% of all leaf iron is concentrated in chloroplasts. The exact role of iron in chlorophyll synthesis is not certain but there is evidence of the involvement of ferrous iron in the condensation of succinic acid and glycine to form γ-aminolevulinic acid. Magnesium is incorporated into the molecule to form chlorophyll, possibly with the catalytic action of iron.