Manganese (Mn++)

Functions

Manganese is essential for many plant functions. Some of them are:

Factors Affecting Availability

High Response Crops

While this is an essential element for all plants, these crops have been found to be especially responsive: alfalfa, beets, cauliflower, citrus, cotton, large-seeded legumes, lettuce, onions, potatoes, small grains, sorghum, soybeans, spinach, sweet corn, and tobacco.

Deficiency Symptoms

Because Mn is not translocated in the plant, deficiency symptoms appear first on younger leaves. The most common symptoms on most plants are interveinal chlorosis. Sometimes a series of brownish-black specks appear in the affected areas. In small grains, grayish areas appear near the base of younger leaves. Manganese deficiencies occur most often on soils with a high pH and/or naturally low Mn content. Conifers will exhibit a general yellowing of the current season's needles.

Toxicity

Manganese toxicity is a relatively common problem compared to other micronutrient toxicity. It normally is associated with soils of pH 5.5 or lower, but can occur whenever the soil pH is below 6.0. Symptoms include chlorosis and necrotic lesions on old leaves, dark-brown or red necrotic spots, accumulation of small particles of MnO2 in epidermal cells of leaves or stems, often referred to as "measles", drying leaf tips, and stunted roots. Sometimes the interveinal tissue will show "puckering" or raised areas in the leaves. Toxic symptoms can sometimes be alleviated by using Iron chelates applied to either the soil or preferably the foliage. Some acid-loving plants such as blueberries, cranberries, Christmas trees, azaleas, etc. may accumulate very high levels of Mn in their tissue due to the required low soil pH. However, these plants normally will tolerate much higher tissue Mn than other species.

Using Manganese in a Fertility Program

Recommended rates of Mn

Method

Rate

Broadcast:

NOT RECOMMENDED

In-row:

1 to 5 lb./A

Foliar:

1 to 2 lb./A

Broadcast applications are not recommended because Mn that is not concentrated in a band or similar method is quickly converted to unavailable forms when it comes into contact with the soil. Liming soils to the proper pH for the crop is the most practical way to avoid the majority of problems with Mn. On high pH soils, the use of acid-forming fertilizers in the row can increase the uptake of Mn, and other micronutrients. One example of an acid-forming fertilizer blend would be one based on monammonium phosphate and ammonium sulfate. Where foliar Mn is used, multiple applications throughout the season are often needed to compensate for soil deficiencies.

Some common fertilizer products containing Manganese

Product

Chemical Formula

Typical Mn Content

Manganese Sulfate

MnSO4h4H2O

23-28%

Manganese(manganous) Oxide

MnO

41-68%

Manganese Chelate

various

5-12%

NOTE: It has been reported that if a Mn-chelate (EDTA) is added to the soil to correct an apparent deficiency problem, the most common result is increased Mn deficiency. This occurs because the affinity of chelates for Iron is greater than their affinity for Manganese and substitution occurs. The Fe-chelate is rapidly taken up by the plant and the ensuing interaction increases the Mn deficiency.