Functions

Iron is essential for many plant functions. Some of them are:

• Chlorophyll development and function.
• It plays a role in energy transfer within the plant.
• It is a constituent of certain enzymes and proteins.
• Iron functions in plant respiration, and plant metabolism.
• It is involved in nitrogen fixation

Factors Affecting Availability

• Soil pH: High soil pH reduces Fe availability while acid soils increase Fe availability. The high pH effect is increased in waterlogged, compacted, or other poorly aerated soils. One factor in this effect is the presence of high carbonates in the soil, which also plays a role in waterlogged soils and in the root rhizosphere reaction to certain other nutrients and fertilizer sources.
• Low Organic Matter: In addition to being a source of Fe, O.M. compounds are able to form Fe complexes that improve availability.
• Saturated, Compacted, or Other Poorly Aerated Soils: In acid soils, this condition can increase Fe availability (to the point of toxicity).
• High Soil P: Excessive amounts of soluble P, or high rates of P fertilizer, have been demonstrated to inhibit Fe uptake in many crops.
• Form Of N Applied: Increased NO3 -N uptake can reduce Fe uptake by causing an anion-cation imbalance in the plant.
• Fe:Zn Balance: Zn deficiency has been shown to increase the Fe uptake of many crops, sometimes to the point of toxicity. Conversely, high Zn availability reduces Fe uptake.
• Fe:Mn Balance: It is well documented that these two elements are antagonistic, and one will inhibit the uptake of the other.
• K:Fe Balance: K appears to play a very specific, but poorly understood role in the utilization of Fe. Some research indicates that low K availability can result in increased Fe uptake.
• Fe:Mo Balance: High levels of available Mo can reduce the uptake of Fe by causing the precipitation of iron molybdate on the root surfaces. This is especially important in alkaline soils where the high pH reduces the availability of Fe while increasing that of Mo.
• HCO3- : Iron deficiency can be induced by the presence of the bicarbonate ion in the soil (saline and alkali conditions).

Deficiency Symptoms

Interveinal chlorosis of young leaves. Severe deficiencies may progressively affect the entire plant turning the leaves from yellow to bleached-white.

Toxicity Symptoms

Iron toxicity is primarily pH related and occurs where the soil pH has dropped sufficiently to create an excess of available Iron. As with some other nutrients, the visible symptoms of Fe toxicity are likely to be a deficiency of another nutrient. Fe toxicity can also occur when Zinc is deficient, or the soil is in a “reduced” condition caused by very wet or flooded conditions. Excess Fe can result in Dark green foliage, stunted growth of tops and roots, dark brown to purple leaves on some plants (e.g. bronzing disease of rice).