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Zinc

First seen: Younger leaves
Signs:Leaves show wide band of yellow and smaller.
Natural Sources: Manure, phosphate rock

Zinc shows as a discoloring of leaves with edges turning upwards

Description: Zinc is a metallic element that is brittle at room temperature. It is used as a coating for iron and steel to prevent corrosion. Zinc occurs in minerals and is commonly found in zinc sulfate (ZnSO47H2O).

Deficiency: Younger leaves show a wide band of yellow bleached tissue and are smaller than normal. Reddish spots then show up in the yellow tissues.


Leaf edges turn upwards

Toxicity: Zinc toxicity is a rare occurrence, and can happen when galvanized tanks or parts are used in a hydroponic system.

Conditions: Zinc is most available in pH conditions from 5.0 to 7.0. Zinc deficiency can be mistaken for leafhopper or root damage.

Zinc requirements in plants

In plants, a small amount of zinc is needed and too much can be toxic. An active site component of many enzymes, most fruits and vegetables have about 0.5mg/100g. Nuts and peas have more.

Zinc can be less available in heavily fertilized soils. When zinc is deficient in corn, tryptophan may be lacking. It may also affect protein formation in other plants, reducing the number of essential amino acids.

Zinc deficiency in plants

Deficiency shows up in younger leaves as stunted or abnormally small leaves. The area between the veins turns yellow and bronze colored spots form around the margins of the upper leaves. Leaf tissue between veins turns a creamish yellow while area along the veins remains green.

Plants have stunted leaves that are curved upwards and look like leaf roll virus. In general, leaves are smaller, internodes shorter and stems are more rigid. Gray brown spots form on leaves half way up the plant and then spread.

Remedy for zinc deficiency

A foliar spray application of 1% solution of zinc sulfate should correct the deficiency. Zinc sulfate can also be mixed with lime or soda ash to form a longer lasting film on leaves. Zinc oxide can also be used which puts fewer residues on the foliage. Heavy residues can encourage scale insects and mites. Leafhopper damage may be mistaken for zinc deficiency. The primary difference is that the leafhopper punctures the midrib of a leaf and causes a yellow discoloration in the form of a v.

Plants suffering from a virus or fungus disease can appear to have a zinc deficiency due to a reduced root system.

Increasing soil pH decreases zinc availability and uptake by plants. Zinc content declines as plants mature. In general, all plant diets should be supplemented with a zinc salt. Zinc (as zinc sulfate) can be added to the water. Most plants have about from 50 to 100 ppm of zinc in dry weight analysis.

Zinc toxicity in plants

Zinc toxicity is rare in plants, but can be caused by systems where galvanized pipes and water containers are used. The zinc becomes available in higher acid situations. Zinc toxicity looks like copper deficiency, because it will reduce available copper to the plant.

Zinc requirements for humans

Zinc in the human body amounts to about 2.5 g and most is stored in the skin. Zinc is essential for wound healing and resistance to infection and inflammation. A typical diet should supply about 7 to 17 mg a day, with from 20 to 30% being absorbed (6). It is absorbed in small intestine and some dietary components reduce Zinc absorbency. Examples are phytase, calcium, fiber, phosphorus, copper , cadmium and chromium (Miller et al, 1979). Phytate, found in all plant seeds and many roots and tubers, interferes with intestinal absorption of Zinc. Zinc must be present in the diets of all animals and must be supplied continuously, for animals only have a small amount available in their bodies (12). Zinc is poorly absorbed after the age of 50.

Zinc deficiency in humans

Signs of zinc deficiency include weight loss, loss of appetite, listlessness, rough and scaly skin, poor night vision, a dull sense of taste, and white spots on fingernails. Wounds that heal very slowly might be caused by a zinc deficiency. Skin problems are often from zinc deficiencies, and a zinc supplement can usually help heal skin disorders..

Zinc is used for enzymes to synthesize protein. Zinc is needed to form collagen and to release Vitamin A, another nutrient crucial to healing. It also fights infection and inflammation. Zinc is used for a variety of skin ointments such as calamine lotion. Low zinc may contribute to gum disease. Zinc may also help body reduce absorption of lead or other possible chemical carcinogens. Zinc sharpens sense of taste, smell and sight, it also reduces body odor. Worldwide zinc deficiency is more widespread than any other deficiency. Zinc sulfate, zinc acetate or zinc gluconate are used as diet supplements (6). Zinc was used as a skin ointments by ancient Egyptians. Bone Zinc and Zinc in hair is unavailable to tissues.

Zinc requirements in animals

Animals that do not have zinc lose their appetite and do not grow very well.

Recommendations: In a hydroponic nutrient, zinc content ranges from 0.02% to 0.05%, usually supplied in zinc sulfate or zinc chelate. A solution of 0.02% zinc amounts to 2000 ppm in dry form and the 0.05% is 5000 ppm. When diluted in water at 100 to 1, these change to 20 ppm to 50 ppm.

Zinc is necessary for human nutrition, with about 20 mg needed per day. Zinc is more available in younger plant tissues and seeds. Assuming a 50 ppm in the produce 500g of peas, beans, peanuts and cereals should supply a daily amount of zinc of

Zinc Toxicity

Zinc is not known to be toxic until it reaches levels approaching 500 mg. Then it can cause drowsiness, vomiting and copper deficiency (Larson, 1992). It can be leached from galvanized containers and pipes, especially in an acid environment, so galvanized products should not be used in a hydroponic system.

Zinc sulfate can be ingested by accident, and induces heavy vomiting. Death usually occurs in 24 hours of taking large doses. Zinc sulfate looks like and can be confused with Epsom salts. It usually takes about 2 ounces to induce death.

Zinc Chloride (ZnCl) is a poison in amounts of about 2 ounces. It is very caustic and can damage tissues.

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