IRON DEFICIENCY

Micronutrients are required by plants in relatively low concentrations compared to the major elements. The seven micronutrients are boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn), which have been identified in the past as trace or minor elements, terms that are no longer used.

Micronutrients are unique among the essential elements since their deficiency is frequently associated with a combination of crop species and soil characteristics. Iron deficiency may be associated with strawberries and other crops on leached sandy soils and on alkaline soils. This is frequently referred to as lime-induced chlorosis.

Iron deficiency symptoms first appear on the younger leaves as a yellowing of the leaf blades with the veins and petioles green. It is called interveinal chlorosis.

Iron availability is controlled by soil pH. Iron is readily available in acidic soil solutions, however, it is tied up in basic soils. Iron is least soluble at pH of between 7.4 and 8.5.

Iron is normally found in high amounts in most soils. Iron deficiency is rarely caused by low amounts in the soil but by low iron availability or mobility due to soil conditions. Iron salts that have low solubility, such as iron oxides, carbonates, phosphates, hydroxides, are formed in certain soil types which makes iron not available to plants.

High levels of carbonate, bicarbonate, and phosphates in the soil may lower the availability of iron by forming salts that have low iron solubility.

Fertilization can affect the availability of iron. High phosphorus decreases the solubility of iron in the plants. Potassium increases the mobility and solubility of iron in plants. High nitrogen fertilization accentuates iron deficiency due to increased plant growth. Large lime applications, which increase soil pH, increase the carbonate levels in the soil and can increase iron deficiency. Over-irrigation increases iron deficiency.

Iron deficiency problems can be corrected with foliar applications of ferrous sulfate or soluble iron chelates. The response to foliar applications can be quick. However, several foliar applications may be required to grow the crop.

Soil applications of soluble forms of iron last longer than foliar applications. However, the plant response may be slower because it has to be absorbed by the roots and translocated to the leaves. Soil applications can be oxidized to more insoluble forms, thus making iron less available to the crop.