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Manganese

Trace element
Manganese is an essential trace element. It is a catalyst that functions in cell membranes and the production of chloroplasts. Soils with a lack of manganese produce plants with a yellow-greenish colour between the nerves of the leaves (this can also occur as a result of lack of other elements like iron or magnesium or other causes). This phenomenon is also called "chlorosis", or "decolourization of leaves". The production of chlorophyll is slowed down if there is a lack of manganese. A shortage of manganese is widespread, special on soils with a pH above 6.2. The pH is more important for the uptake of manganese in plants than the amount of manganese in the soil. The critical manganese deficiency level for most plants ranges from 15 to 25 mg/kg in the dried leaves. The toxic concentration of manganese to plants is more variable, depending on both plant and soil factors. Generally, most plants are affected by a manganese content around 500 mg / kg analyzed in dry leaves. An adequate soluble silicate supply to plants is reflected in the easy transport of Mn and a more homogeneous Manganese distribution in the plant. Other elements like magnesium, potassium, sodium and ammonium affect the uptake of manganese and vice versa.

Manganese analysis

In our analysis we analyze two fractions of manganese in the soil. The first is the reduced, soluble fraction of manganese, extracted with a very light concentration of neutral calcium chloride. The second one is the total amount of extractable manganese. Most of this manganese is in the oxidized or attached to soil particles.

Manganese toxicity

An abundance of manganese can be toxic for some type of plants. This effect occurs almost only in glasshouses, when soil with high total manganese has been treated with steam. Sometimes purple spots appear on leaves, which will lead to a necrosis. Both fractions of manganese will be high in these circumstances. A high soluble silicon and calcium ions in the soil reduces the manganese toxicity. High manganese decreases the uptake of calcium in a plant.

Fertilization with manganese
If the pH-value is this high, then plants cannot absorb manganese. Fertilization will then only be effective if the fertilizer is sprayed onto the leaves or when special manganese chelates are applied. Some chelates don't work at high pH levels. On leaves manganese sulphate and manganese chelate will be effective. On high pH levels the plants will have also difficulty by taking up other trace elements. When only one of the trace elements is applied, signs of other trace element shortage can appear. Our advice is in these situations to use a mix of trace elements. When it is known that plants on a specific soil suffer from a shortage of manganese, the foliar application of manganese have to start before the signs of manganese shortage appear. Manganese is translocated within plants relatively rapid.

Manganese and oxygen

If the soil structure is bad and/or if the oxygen demand in de soil is high, the amount of reduced, soluble manganese in the soil will be elevated. To normalize this situation, aeration (oxidation) of the soil may give the desired result. A healthy soil life requires a sufficient amount of air. When also the biological oxygen demand and the oxygen status are already affected, the duration of healing can take several years. Especially when also oxygen shortage in the sub soil is detected. On basis of these results, we recommend a special soil treatment, depending on the situation at hand.

Manganese and natural soil chelates.

The in water-soluble humic acids and some other water-soluble organic compounds in the soil water can bind manganese temporally. It works like a synthetically formed chelate. When many trace elements like manganese in the form of metal ions are bound by these natural chelates, the amount of free ions that can be taken up by a plant is also higher. Therefore a high amount of natural chelates in the soil is benedictional to the uptake of trace elements as manganese.

More on manganese (Mn)

Manganese is one of the most abundant trace elements in the lithosphere, and its common range in rocks is 350 to 2000 mg/kg. The utmost part of this manganese is not in a form that a plant can take up. During weathering secondary manganese containing minerals will be formed. Manganese can show in ion form in 3 forms: 2+, 3+ and 4+. These Because of this variety of ions form, that change constantly, manganese is a more complex element. This capacity of change in valence makes manganese a catalyst in processes in the soil and within the plant. Some manganese 4+ containing minerals like MnO2 are black. Sometimes they can be found in lithe or bigger concretions that can be seen in a soil, but also on the bottom of the Atlantic Ocean. Manganese 4+ is the oxidized form; Mn 2+ is the reduced form. The Mn 3+ form is in between. Oxidizing elements in the soil will transform Mn 2+ to Mn 3+ of even Mn 4+. Reducing elements like Iron(II) and Chromium(III), reduced S, phenols and other easily oxidized organic compound transform Mn 4+ via Mn3+ to Mn 2+.