IMPORTANCE FOR PLANT LIFE

METABOLISM

Manganese plays a role in nitrate reduction and in the synthesis of amino acids that form proteins. For this reason, manganese deficiency always leads to growth disorders and therefore to yield losses. It is a component of many enzymes and is involved in chlorophyll synthesis, which explains why deficiency causes chlorosis (yellowing) between the veins of young leaves.

During periods of full and vigorous vegetative growth, manganese—together with nitrogen and magnesium— becomes one of the key success factors for many crops. In other words, without sufficient Mn, plants cannot fully express their growth and yield potential.

UPTAKE MECHANISMS

Changes in soil moisture can increase or decrease Mn availability. Therefore, even in well-drained and well-aerated soils, manganese can become the first limiting factor. Manganese occurs in soil as Mn²⁺, Mn³⁺, and Mn⁴⁺, but the primary form taken up by plants is Mn²⁺.

INTERACTIONS AND SPECIFIC FEATURES

Applying manganese directly to the soil is not always sufficiently effective because Mn availability is strongly influenced by soil properties and environmental factors. For this reason, in many cases, intervention via foliar application is more effective, and ideally these applications should be repeated several times throughout the vegetative growth period.

MANGANESE IN SOIL

MANGANESE AVAILABILITY

Manganese availability is largely influenced by soil pH, and deficiencies are most common in calcareous soils. Mn is most available between pH 5 and 6.5. At very low pH values (<5), manganese toxicity may occur.

Mn²⁺ is readily chelated by organic molecules; this is supported by high organic matter content and can reduce Mn availability over time. Other nutrients such as copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) may also inhibit Mn uptake.

Soils rich in granite and sandstone are naturally poorer in manganese than soils of volcanic or sedimentary origin. High organic matter content negatively affects manganese solubility. Liming practices can similarly reduce Mn availability.

Dry weather conditions reduce the amount of available manganese. In winter, in waterlogged and saturated soils, manganese presence is often observed as bluish-gray mottling.

DIFFERENT FORMS OF MANGANESE IN SOIL

Manganese can occur in different forms in soil:

• Oxidized, trivalent (Mn³⁺) or tetravalent (Mn⁴⁺) forms: These oxidized forms are the most common Mn forms in soil and are very difficult for plants to take up.

• Divalent Mn²⁺ form: This is the form directly taken up by plants. It can be adsorbed onto clay minerals and organic matter and is also present in the soil solution.

SENSITIVITY TABLE & SYMPTOMS

Because manganese is relatively mobile within the plant, deficiency symptoms are generally seen first on young leaves and appear as interveinal chlorosis (yellowing between veins). This can be confused with magnesium (Mg) or iron (Fe) deficiency.

With Mn deficiency, symptoms in some species may start more on the newer/upper leaves; in Fe deficiency, the contrast between veins and the yellowed areas is sharper. In Mg deficiency, older leaves are typically affected first. Therefore, leaf age and the vein–contrast relationship are critical for diagnosis.

EXCESS & REQUIREMENT

Excess manganese in soil can have negative effects on plants, especially under wet and water-saturated conditions or during prolonged rainy periods. Similarly, oxygen-poor (anaerobic) soil conditions can also lead to problems caused by manganese excess.

ORIGIN & FORMULATIONS

Effective Mn compounds for foliar application include sulfates, oxides, nitrates, and carbonates. In general, after manganese is applied to leaves, it penetrates plant tissues within a few days; this makes it possible to supplement nutrients multiple times during vegetative growth.

The goal of selected formulations is to extend Mn nutrition over a longer period in foliar applications and thus limit the number of treatments. This reduces labor while making nutrient use more efficient.

KEY FACTORS

MANGANESE CONTENT IN SOIL

Most manganese in soil is present in oxide form; nevertheless, Mn analyses performed with EDTA or DTPA extraction are good indicators for evaluating plant-available manganese.

ORGANIC MATTER

High organic matter content leads manganese to form Mn–organic matter complexes, which limits the plant-available form of Mn. In other words, when organic matter is very high, the risk of Mn deficiency may increase.

TEXTURE

Light, sandy soil textures accelerate manganese oxidation due to continuous air circulation. This reduces Mn²⁺ and, over time, can lead to Mn deficiency.

CLIMATE

Climate strongly affects Mn²⁺ availability. Deficiency is most often observed under cool and wet conditions. However, even under favorable growth conditions, manganese can oxidize and become unavailable to plants; therefore, climate and soil oxidation status should be evaluated together.

pH

pH is a decisive factor for manganese availability. When pH < 6, the risk of Mn deficiency is generally low. At pH 7 and above, trivalent forms (Mn³⁺) become dominant and deficiency risk increases.

Conversely, Mn toxicity can occur in very acidic, Mn-rich soils. Frequent liming can raise pH rapidly, causing manganese to become blocked and leading to deficiency symptoms.