Manganese (Mn) functions primarily as part of enzyme systems in plants. It activates several important metabolic reactions and plays a direct role in photosynthesis. Manganese accelerates germination and maturity while increasing the availability of phosphorus (P) and calcium (Ca).
Manganese (Mn) is taken up by plants as the divalent cation Mn2+. It functions primarily as a part of enzyme systems in plants. It activates several important metabolic reactions and plays a direct role in photosynthesis by aiding in chlorophyll synthesis. Manganese accelerates germination and maturity, while increasing the availability of phosphate (P) and calcium (Ca).
Manganese is immobile in plants, so deficiency symptoms appear first on younger leaves, with yellowing between the veins. Sometimes a series of brownish-black specks appear. In small grains, grayish areas occur near the base of younger leaves. Manganese deficiencies are most common in high organic matter soils and in those soils with naturally low Mn content and with neutral to alkaline pH. Delayed maturity is another deficiency symptom in some species. Whitish-gray spots on leaves of some cereal crops and shortened internodes in cotton are other Mn-deficiency symptoms.
Manganese deficiencies are often associated with high-pH soils, which may result from an imbalance with other nutrients such as Ca, magnesium (Mg) and Iron (Fe). Soil moisture also affects Mn availability. Deficiency symptoms are most severe on high organic matter soils during cool spring months when soils are waterlogged. Symptoms disappear as soils dry and temperatures warm.
Manganese deficiencies can be corrected in several ways:
- If liming caused the deficiency, keep soil pH below 6.5.
- Mix soluble salts, such as Mn sulfate (MnSO4), with starter fertilizer and apply in bands. High P starter fertilizer helps mobilize Mn into the plant.
- A field deficiency symptom can be corrected by foliar application.
In some soils, an extremely acidic pH may cause Mn toxicity to crops. Soil pH must be 5.0 or lower before significant toxicity threatens. Yet, toxic Mn levels in plants have been measured up to a pH of 5.8. Liming will eliminate this problem.
Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant
(i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.