Essential Nutrients

Manganese (Mn)

Form used by plants:

Mn²⁺

Important functions:

• Enzyme activator (decarboxylase, dehydrogenase, and oxidase enzymes)

• Assists iron in chlorophyll formation

• Assimilates CO₂ in photosynthesis

• Essential for phosphorus and magnesium uptake

• Prominent in chloroplast membrane (structure containing the high absorbing chlorophyll pigment and C-assimilating mechanisms)

• Important in N metabolism and assimilation

Ideal foliage range for apple leaves:

25-100 ppm leaf dry weight

Ideal fruit concentration:

Ideal soil range:

> 1.5 ppm 

Deficiencies are most common on soils with pH . 7.0. Toxicities may occur on acid soils. 

Mn is relatively not mobile in soils.

Best indicators: 

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Mobility in plant:

Not remobilized within plant

Deficiency symptoms:

Vegetation symptoms: interveinal chlorosis developing in older leaves first.  In severe cases, heavy defoliation may occur.  Rust spots or a mottled pattern may be an indication on some plants.

Increased risk of Mn deficiencies:

Availability of Mn decreases as pH increases (at soil pH 6.3, Mn becomes insoluble)

Excess problems/Interactions with other elements:

• In acid soils, toxicity may occur especially on Delicious and Jonathan apples.  Signs may include chlorosis, early leaf abscission, reduced flower bud development, and internal bark necrosis.

• Excess iron, copper, or zinc may reduce Mn absorption.

• Excess sodium or potassium may adversely affect Mn uptake.

• Excess Mn encourages iron deficiency.

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