Manganese deficiency accurs most often on high organic matter soils, on soils with neutral to alkaline pH and soil that are naturally low in Manganese content.

Deficiency symptoms:

Plants show yellowing, veins remain green. Mature leaves may be 'mottled.' First signs of deficiency often show up as small pin-head sized brown specks on the leaves. Flower formation is reduced. In cotton the young leaves are yellow (lower leaves are less affected) sometimes grey to reddish-grey between veins. The veins remain green. Mn deficiency will delay maturity.

Functions in plant:

Aids in chlorophyll formation: serves as a catalyst in enzyme reactions such as breakdown of carbohydrates, formation of vitamins and nitrogen transformation.

Mobility in plant: Relatively immobile.
Mobility in soil: Relatively immobile (Soluble forms are usually fixed into insoluble forms within 1 year.)
Influence of soil pH: The availability of Mn drops off sharply as the pH goes from 5.0-7.0.
Factors affecting level: High pH; low organic matter usually will give low Mn levels; some sandy soils are low in Mn; poorly drained, calcareous silts and clays are often low.
Factors affecting utilisation: pH; high levels of Fe, Cu and Zn may reduce uptake of Mn; problems show up more during dry years-apparently because of better drainage, thus more oxidation and less solubility of Mn.
Adequate level in plant: 23 ppm in soybeans, 25-30 ppm in cotton, sugar cane 40-250 ppm, wheat 10-300 ppm.

Corecting deficiencies:

Broadcast 5-20 kg per hectare (rate depends on soil pH and particular crop sensitivity); spray- 0.5-0.75 kg in 2-400 litres water per hectare. Mn sulphate is preferred over Mn oxide unless the pH of the fertilizer is very low.

Remarks:

The more acid forming the fertilizer, the more available the Mn. Mn toxicity occurs quite often below pH 5.0 plants vary widely in their response to Mn.