Molybdenum requirements of plants
Molybdenum is needed in trace amounts. It acts as an electron carrier in converting nitrate (NO3-) or ammonium(NH4+).
This means it is important in allowing plants to use the nitrogen in the nutrient.
Legumes, such as peas, beans and peanuts, need molybdenum for the bacteria that form nitrogen fixing root nodules (Sprague, 1964).
Molybdenum deficiency in plants
A deficiency is usually seen in acid soil or acid media conditions.
It often looks like nitrogen starvation as molybdenum deficiency reduces the plants' ability to utilize nitrogen.
Edges of leaves curl up and die with a brown color and there is some brown discoloration of the leaf edges. Yellow and orange spots start to appear on the outside margin of the leaves. It first effects the older lower leaves.
Whiptail - a condition caused by molybdenum deficiency where the plant leaf does not fill out, and the leaf midrib grows long and twisted like a whip. It is often seen first on the shaded portion of the plant.
Saline conditions - In saline conditions the first sign in leaves is a yellowing of leaves.
Remedy to molybdenum deficiency
A foliar spray is made of 1 ounce of sodium or ammonium molybdenate in 100 gallons of water. Phosphate fertilizers usually have enough molybdenum as an impurity to act as a molybdenum supplement for soil or nutrient water.
Molybdenum needs in humans
Molybdenum is stored in the body in amounts as little as .1 ppm of body tissue (Guthrie, 1971). It is used in an enzyme, xanthine oxidase that aids in mobilization of iron from liver, and gathers excess nitrogen in the body turning it into uric acid. It is also a part of aldehyde oxidase, which oxidises fat (Kirschmann, J.D., 1975).
Human daily requirements for molybdenum
Adults need 0.15 to .5 mg. Only 20 to 30% of ingested molybdenum is absorbed (12). Grains, legumes and dark green leafy vegetables are rich sources. Amounts differ due to amount available in soil. Food completely dependent upon soil content (Kirschmann, J.D., 1975) and it should be included in nutrient water of hydroponic culture.
Molybdenum deficiency
Since so little molybdenum is needed by the human body, a deficiency is rare. When it is induced in research, it looks like anemia, or iron deficiency.
Molybdenum toxicity
Too much molybdenum can trigger a copper deficiency (6). Toxicity is characterized by diarrhea, anemia, depressed growth (Kirschmann, J.D., 1975). Scouring in cattle (diarrhea) is caused by high amounts of molybdenum and can be corrected by giving more calcium.
Recommendation: In a hydroponic nutrient, molybdenum should be added at a rate of 1 microgram per liter of solution. This allows for enough molybdenum to grow a large crop and still includes enough molybdenum for human nutriention.
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