Manganese fertilizers

Manganese content in soil

Soils contain significant reserves of manganese: in yellow soils — more than 1%, in sod-podzolic and chernozem soils — 0.1–0.2%. However, most of it is in the form of poorly soluble oxides and hydroxides. In soil, manganese is present predominantly in divalent form; in silicates and oxides it can replace Fe²⁺ and Mg²⁺, which leads to their leaching. In acidic soils, manganese forms iron-manganese nodules with iron hydroxides.

Manganese is contained in the humus layer and the silty fraction of the soil. In acidic soils it is present in the form of a poorly mobile divalent form that is poorly available to plants. Manganese mobility increases with the application of ammoniacal fertilizers.

Plants can absorb compounds of divalent manganese. Manganese compounds of other valences are unstable, especially the trivalent form. In a reducing environment, Mn⁴⁺ is present, forming poorly soluble compounds. Under conditions of excessive moistening, anaerobic conditions are created that intensify reduction processes, increasing the content of available manganese. On irrigated lands, manganese is not applied. In dry weather, primarily on calcareous soils with an alkaline reaction, divalent manganese transforms into tri- and tetravalent forms that are unavailable to plants. Under these conditions, the effectiveness of manganese fertilizers increases. Manganese mobility increases with the application of ammoniacal forms of nitrogen fertilizers.

Lime and alkaline forms of fertilizers reduce manganese mobility and its uptake by plants. Sod-podzolic soils, as a rule, contain the greatest amount of manganese. Sugar, fodder and table beet, wheat, maize for grain, barley, alfalfa, vegetable and fruit crops especially suffer from manganese deficiency.

As a result of the high manganese content in soil, its amount in the soil solution can reach 2200 µg/L, with the formation of complexes with fulvic acids. At a near-neutral reaction of the soil solution, plants may experience manganese deficiency because of the transition into poorly soluble compounds. In practice, to prevent the binding of metal ions by the soil and to improve their availability to plants, chelates of manganese and iron are used, which are applied with irrigation water and in foliar feeding.

Chelates of trace elements are widely used. For example, in Sweden foliar feeding of sugar beet is carried out with a chelate containing 6% manganese; EDTA is used as the ligand. In experiments conducted in Great Britain, treatment of crops of spring wheat increased yield from 2.8 to 4.7 t/ha.

Manganese fertilizers are used in Ukraine. A positive effect from their use is noted on chernozems, calcareous, solonetzic and chestnut soils with a low content of plant-available manganese. On soils of the Non-Chernozem zone, manganese is effective when its content is 25–55 mg/kg of soil; in the Chernozem zone — 40–60 mg/kg of soil; on serozems — 10–50 mg per 1 kg of soil.

Manganese fertilizers are applied on gray forest soils, slightly leached chernozems, solonetzic and chestnut soils under oats, wheat, fodder root crops, potatoes, sugar beet, maize, alfalfa, sunflower, fruit and berry, citrus and vegetable crops.

Soils requiring the use of manganese fertilizers include calcareous chernozems, chestnut and brown semi-desert soils of the Volga region, North Caucasus, Urals and Western Siberia. On northern sod-podzolic soils, these fertilizers most often do not produce a positive effect; in some cases they negatively affect plants.

K. K. Gedroits and O. K. Kedrov-Zikhman pointed to the positive effect of manganese on limed soils. Manganese fertilizers do not always have a positive effect on various soils of the south of the European part of Russia. Probably, when applying these fertilizers, attention should be paid to alkaline, neutral and calcareous soils that are light in texture.

On chernozems, the yield increase of sugar beet from the application of manganese fertilizers is 1.0–1.5 t/ha; the sugar content of roots increases by 0.2–0.6%; the yield of grain crops, including winter wheat, increases by 0.15–0.30 t/ha.

Manganese fertilizers

Wastes from manganese ore industry enterprises are used as manganese fertilizers; their manganese content is 10–18%. They also contain approximately 20% calcium and magnesium, 25–28% silicon oxide, 8–10% sesquioxides and a small amount of phosphorus.

Because of its high cost, manganese sulfate is mainly used in greenhouse vegetable growing. Considering that manganese is effective against the background of phosphorus fertilizers, it is advisable to produce superphosphate enriched with manganese.

Manganized superphosphate is light-gray granules containing 1.0–2.0% manganese and 18.7–19.2% P₂O₅. It is obtained by adding 10–15% manganese sludge to powdered superphosphate during granulation.

Manganese sulfate, or manganese sulfate (MnSO₄) — a fine-crystalline salt, manganese content 32.5%, highly soluble in water.

Manganized nitrophoska contains nitrogen, phosphorus, potassium, and 0.9% manganese, which is readily available to plants.

Methods of application

Manganese fertilizers are applied to the soil, used for pre-sowing seed treatment and for foliar feeding. For application to the soil under sugar beet, grain crops, maize, vegetables, oilseeds and other crops, manganized superphosphate is used at a rate of 2–3 c/ha with incorporation by plough during plowing or pre-sowing cultivation. It is also applied in rows at sowing at a rate of 0.5–1 c/ha. Superphosphate can be replaced by nitrophoska; the dose is calculated based on the content of nitrogen, phosphorus and potassium. Before sowing, manganese sludge can also be applied at a rate of 0.5–2 c/ha.

When applied to the soil, the manganese dose calculated as the element is 2.5 kg/ha. Approximately one third of manganese fertilizers for agriculture is needed in the form of manganese sulfate for foliar feeding and pre-sowing seed treatment.

For seed dusting, 50–100 g of manganese sulfate mixed with 300–400 g of talc is used to treat 100 kg of seeds of sugar beet, wheat, barley, maize, peas, sunflower. Dusting can be combined with seed dressing. For foliar feeding of field crops, the application rate is 200 g of manganese sulfate per 1 ha; for spraying fruit and berry crops — 600–1000 g/ha. For aerial spraying — 150–200 g dissolved in 100 L of water per 1 ha; for ground spraying — 30–50 g per 100 L.

References

1. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.

2. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.