Iron

Definition: Iron is a silvery white metal that oxidizes in moist air and forms rust. About 5% of the earth's crust is made of iron. Iron is commonly used in nails for use in carpentry, and in some cooking and food storage utensils.

Deficiency: Iron is immobile so signs show up in young leaves. Younger leaves go yellow, then white. Veins go lighter in color. Older leaves stay green.

Iron deficiency in corn shows up between veins at first

Interference: Too much copper can interfere with iron uptake.

Iron needs in plants

Iron is required for chlorophyll synthesis. Iron is comparatively immobile in the plant, so deficiencies show up in the younger portions of the plant. Utilization of iron is dependent upon pH of nutrient and media and high pH or 7.0 will make iron unavailable.

Iron deficiency in plants

Iron deficiency inhibits growth and development. The deficiency shows up as chlorosis, or the loss of chlorophyll of younger tissues. Since both green and yellow pigments are effected, iron deficient leaves first go clear yellow and then white in color. Veins will also lighten in color. Leaves that developed before the deficiency remain green in color.

If pH is over 7, ferrous ions (Fe²⁺) are oxidized to ferric ions (Fe³⁺) and the resulting insoluble ferric sulfate precipitate is not available to plants. So iron deficiency is common in alkaline soils or media conditions, and in alkaline waters.

Since a common reason for unavailable iron is the pH of the water, lowering the pH may make the iron available. A rusty nail or other piece of scrap iron can be placed in the water. The early Greeks treated anemia by drinking water with a rusty sword in the container.

Ferrous sulfate (FeSO₄.7H₂O) of 2.5 to 4.0% can be added to water or sprayed on plants to correct an iron deficiency. The spray should be used at least once and not more than three times.

Excess copper in the water can cause iron deficiency. This can occur after copper based sprays have been used to control fungus. A solution is to flush the system, empty nutrient water and flush media with clear water.

Chelates prevent phosphate precipitation of iron. When iron is used by plant excess chalates in solution may bind with copper and zinc, reducing their availability in nutrient water. The amount of iron also depends upon the amount of manganese, potassium and other elements in tissue. There is an antagonism between iron and manganese.

Many minerals used to supply calcium and phosphorus contain iron. Ground limestone, oyster shell, and many forms of calcium phosphate contain 2000-5000 PPM iron. The water supply might have adequate iron for plant growth.

Although iron is a required nutrient for plants, the available iron can vary according to plant species, growing conditions and iron available to plant. Iron levels in plants vary from 35 to 500 PPM of dry weight. Soybean products show good iron availability if grown in good available iron conditions (Fritz, 1973). Leafy green vegetables, legumes, nuts and whole grain cereals have between 2 to 4 mg per 100g. Fruits and potatoes have between 0.3 and 1.2 mg/100g.

Iron needs of humans

A human body is made up of about 4 to 5 grams of iron in a 70 kg body. It is an essential part of blood.

The lack of iron in the human diet leads to anemia abnormally low blood hemoglobin levels.

Human daily intake needs

Most healthy diets should have between 10-14 mg per day and 15 to 20 mg/day can be lost during menstruation. A pregnant woman can supplement 30-60 mg/day. About 1 mg/day is lost in urine and sweat. Iron is poorly absorbed from the intestine, only about 10% of intake absorbed in the upper part of small intestine (1).

Absorption is affected by:
1) the age, how much iron is in the body, and state of health of the individual
2) conditions in the gastrointestinal track
3) amount and proportions of various other compounds of diet both inorganic and organic (12).

In the acid environment of the stomach, ferrous and ferric ions occur as soluble, hydrated ions Fe(H2O)6 2+ and Fe(H2O)3+ as pH goes to 8 in duodenum so much less sodium hydroxides are formed and very little iron is absorbed. From 8 to 10% of iron in plant foods is absorbed, and only 2.5% of spinach.

Vitamin C and vitamin E can increase the uptake of plant iron. Vitamin C increases uptake because it reduces Fe+3 to Fe+2. Boiling water can reduce iron content in vegetables as much as 20% (Skeets et al, 1931).

Balance of calcium and phosphorus hinders iron absorption, but if calcium is present it will combine with phosphates and free iron. Excessive levels of calcium, phosphorus, manganese, zinc or copper or presence of gossypols, phytins or tannins will increase daily iron requirements. Lack of hydrochloric acid, administration of alkalis, high intake of cellulose, coffee and tea interferes with iron absorption (Kirschmann, J.D., 1975).

High phosphates in the diet reduces iron absorption, presumably by the formation of insoluble ferric phosphate and phytate.

Drinking water

Drinking water can include available iron. Putting a rusting piece of pure iron in drinking water will increase daily supply.

Iron toxicity

Iron vessels for cooking can overload iron intake and cause cirrhosis of the liver. Bacteria such as E. coli, require iron to grow so to inhibit bacteria growth, available iron can be restricted (1). High dietary levels of copper, manganese, lead and cadmium increase iron requirements by competing for absorption sites in intestinal mucosa.

Additional needs for iron

A high carbohydrate diet of cassava, potatoes, bread, and white rice can reduce available iron. Hookworms consume 1 ml blood/day.

Chelates

A chelate is a form of iron that has the iron ion attached to an organic molecule that allows the iron to be available in a variety of conditions. When the chelate is broken down and iron ion has been absorbed, the chelate is left in the tissues and can rebind with other ions such as zinc and copper.