Zinc trace element. Functions. Signs of Deficiency and Excess – Hydroponics

Zinc is one of the most important trace elements – it is vital for plants, but it is required in very small quantities. Zinc is one of the most common causes of micronutrient deficiencies in crops worldwide and causes large losses in crop production and crop quality. Zinc supplementation when needed provides a more obvious response than any other micronutrient, and zinc deficiency also causes more severe symptoms than other micronutrient deficiencies.

Zinc functions

Zinc is found in plants as a free ion, or as a complex with a variety of low molecular weight compounds, or as a component of proteins and other macromolecules. It is an essential component in many enzymes, where it acts as a functional, structural, or regulatory cofactor; A large number of zinc deficiency disorders are associated with a violation of the normal activity of enzymes (including the activity of the main photosynthetic enzymes).

Zinc is associated with growth hormone, auxin – low levels of auxin cause stunted growth of leaves and shoots. It plays an important role in the formation and activity of chlorophyll, and it is involved in protein synthesis. Zinc is also important for carbohydrate metabolism and plays an important role in moisture absorption (plants with a normal zinc diet have an increased drought potential).

Zinc deficiency

Zinc deficiency symptoms include:

• Chlorosis – yellowing of the leaves; Often interlingual; In some species, young leaves are most affected, but in others, both old and new leaves are chlorotic.
• Necrotic spots – death of leaf tissue in areas of chlorosis.
• Leaf bronze – Chlorotic areas may turn bronze.
• Delayed plant growth – may occur as a result of a decrease in the growth rate or a decrease in the internode.
• Dwarf leaves – small leaves that often show chlorosis, necrotic spots or bronzing.
• Malformed leaves – the leaves are often narrower or have wavy edges.

In small crops, shortened shoots form clusters of small, distorted leaves near the growing tip. Flowers and pods fall out, and yields are sharply reduced.

Examples of zinc deficiency symptoms

From left to right: zinc deficiency in avocado, barley, cotton, corn (three images), rice, soybeans, wheat.

In tomatoes, zinc deficiency shows a progressive case of interveinal necrosis. In the early stages, younger leaves turn yellow and necrotic spots develop in the interveinal upper surfaces of mature leaves. As the deficiency progresses, these symptoms develop into intense interveinal necrosis, but the main veins remain green, as in iron deficiency symptoms.

In strawberries, young leaves first develop yellow interveinal chlorosis within the leaf, while the outer edge remains green. This creates a halo effect. The leaf blades are usually narrower and elongated. With serious defects in the interdental areas, necrosis may develop.

Difficulties in determining zinc deficiency

Zinc deficiency is often confused with:

• Manganese deficiency – the yellowing between the veins resembles “islands” of yellow areas, rather than a continuous discoloration of the leaves.
• Boron deficiency – small cupped leaves, poor fruit and bumps in the internodes.
• Magnesium deficiency – yellowing starts from the edge of the leaf;
• Iron deficiency – yellowing between small leaf veins, almost white over time.
• Herbicidal damage – strong elongation of the edge teeth and distortion of the leaf shape.

Excess zinc

Zinc toxicity causes pale green chlorosis of new leaves. If the toxicity is severe, light brown spots may appear between the veins. Older leaves can wither and look sluggish. All leaves are greener than they should be. Zinc toxicity in hydroponic systems can be caused by water pollution. It is known that contact of nutrient solutions with galvanized pipes and fittings results in the toxic effects of zinc.

Sources of

1. IPNI Crop Nutrient Deficiency Image Collection.
2. Practical Hydroponics & Greenhouses . October . 2016