Essential Nutrients

Zinc (Zn)

Form used by plants:

Zn²⁺

Important functions:

• Component or regulator cofactor of enzymes (dehydrogenase, proteinase, and peptidase enzymes)

• Influences plant hormone proteins, for example  auxin development, especially IAA (i.e., aids in the normal growth and fruiting processes).

• Promotes starch formation

Ideal foliage range for apple leaves:

15-60 ppm

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Ideal fruit concentration:

Ideal soil range: 

0.5-0.75ppm (available Zn not total Zn levels)

Zinc is not very mobile in soils.

Best indicators: 

Mobility in plant:

Not remobilized within plant

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Deficiency symptoms: 

• Young leaves are affected first. 

• Leaves are smaller and narrower than normal ("little leaf").

• Rosetting of leaves occurs.

• Blind wood

Increased risk of Zn deficiencies on:

• Trees on sandy soils containing limited quantities of Zn

• Soils high in P and Ca

Excess problems/Interactions with other elements:

• Excess phosphate may encourage Zn deficiency
• Heavy N fertilization intensifies Zn deficiency. However, application of N fertilizer can stimulate plant growth and increase Zn requirements.  Acid-forming N fertilizers will increase the uptake of both native and supplemental Zn. Neutral to basic products are known to depress Zn uptake.
• Excess Zn encourages iron deficiency and reduces manganese absorption
• Other metal cations, including copper(Cu²⁺), iron(Fe²⁺), and manganese (Mn²⁺), inhibit zinc uptake
• Application of calcium sulfate added to a slightly acid soil can increase the Zn and Fe concentrations in plants.

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