Iron (Fe) is essential for crop growth and food production. Plants take up Fe as the ferrous (Fe2+) cation. Iron is a component of many enzymes associated with energy transfer, nitrogen reduction and fixation, and lignin formation.
Iron (Fe) is involved in the production of chlorophyll, and Fe chlorosis is easily recognized on Fe-sensitive crops growing on calcareous soils. Iron also composes many enzymes associated with energy transfer, nitrogen reduction and fixation, and lignin formation. Iron is associated with sulfur in plants to form compounds that catalyze other reactions.
Iron deficiencies are mainly manifested in yellowed leaves that result from low levels of chlorophyll. Leaf yellowing first appears on the younger, upper leaves in interveinal tissues. Severe Fe deficiencies cause leaves to turn completely yellow or almost white, and then brown as leaves die.
Iron deficiencies occur mainly in calcareous (high pH) soils, although some acidic, sandy soils low in organic matter also may be Fe-deficient. Cool, wet weather enhances Fe deficiencies, especially on soils with marginal levels of available Fe. Poorly aerated or highly compacted land also reduces Fe uptake by plants. Uptake of Fe decreases with increased soil pH, and is adversely affected by high levels of available phosphorus, manganese and zinc in the ground.
Since soil applications of most Fe sources are generally ineffective for correcting Fe deficiencies in crops, foliar sprays are the recommended method. The application rate should be high enough to wet the foliage, so spraying a 3 to 4 percent FeSO4 solution at 20 to 40 gallons per acre is typical. Including a sticker-spreader agent in the spray helps improve its adherence to the plant foliage for increased Fe absorption by the plant. Even so, correcting chlorosis may require more than one foliar Fe application.
Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant
(i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.