Photosynthesis Requires Manganese

Though manganese is the last micronutrient discussed in this five-part series, it is just as important as the others, which were boron, copper, iron and zinc. Crops grown in Western Canada that show high response to manganese application include alfalfa, soybeans, large seed legumes and some small grains. If detected early enough in a crop year, a manganese deficiency can be corrected and prevent yield loss.

Manganese works in areas different from the other micronutrients. Manganese’s main function is in the photosynthetic process, a key part of proper plant growth and function. Manganese is essential for the assimilation of carbon dioxide in the photosynthetic process, and in electron transportation in photosynthesis. The Hill Reaction that is part of splitting water in photosynthesis also uses manganese.

The micronutrient also helps with assimilation of nitrogen in the plant. And it acts as an activation agent in the formation of fat enzymes, and helps in the formation of riboflavin, carotene and ascorbic acid.

WHAT DOES DEFICIENCY LOOK LIKE?

You’ll see symptoms of manganese deficiency in the newer leaves first. The most common symptom is interveinal chlorosis, a yellowing or whitening of the leaf between the veins while the veins stay green. As the deficiency continues, brown or reddish specks may appear in the affected areas of the plant. In more severe cases a lack of manganese can cause general stunted growth.

WHAT CAUSES DEFICIENCY?

As with most micronutrients we have looked at in this series, soil pH plays a role in manganese availability. Higher pH (alkaline) soils reduce nutrient availability and low pH (acidic) soils increase availability. Soil types above 5.8 to 6.5 pH start showing signs of manganese deficiency in susceptible crops. Manganese is stored in organic matter and soils with extremely high organic matter that is not broken down can cause deficiency symptoms. Soils high in iron and molybdenum can inhibit manganese availability.

Manganese is also susceptible to nitrogen stresses. If the crop cannot access enough nitrogen, then it will also have problems accessing manganese.

Manganese can also be a part of the anion effect. This is when certain anions applied during fertilization can have a positive enhancement on the uptake of other nutrients. Fertilization with chlorine, NO3 and SO4 has this effect on manganese.

HOW TO APPLY MANGANESE

The only recommended applications are foliar and in-row. That’s because manganese that is not applied in a row or in a non-concentrated method is quickly converted to non-plant available forms and lost. Manganese is only really applied at one to two pounds per acre. A foliar application of one pound per acre with at an application rate of 30 gallons of water an acre can correct the deficiency for that growing season. In extreme situations, a higher rate will be required in the first application and a second application may be needed if symptoms persist. Manganese is best applied in a sulphate form versus a chelate form. That’s because manganese sulphate dissolves easily in water. Also the sulphate form is much safer for crops in a foliar application. If you use a chelate form, be careful not to over apply and cause leaf burn. In trying to prevent plant damage with a chelate form, you may need to apply twice to get the necessary level of manganese available to the crop.

Jay Peterson farms near Frontier, Sask.

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Jay Peterson farms near Frontier, Sask.

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