Michigan State University Extension
Soils & Soil Management - Fertilizer - 05209705
07/10/97
Secondary and Micronutrients for Vegetables and Field Crops
Extension Bulletin E-486, Revised August 1994
By M.L. Vitosh, D.D. Warncke and R.E. Lucas Department of Crop and Soil Sciences Michigan State University Extension
Manganese deficiency in crops is the most common micronutrient problem in Michigan. The micronutrient manganese should not be confused with magnesium, a secondary nutrient. Manganese is mainly absorbed by plants in the Mn++ ionic form. Manganese may substitute for magnesium by activating certain phosphate- transferring enzymes, which in turn affect many metabolic processes. A high manganese concentration may induce iron deficiency in plants.
Manganese availability is closely related to the degree of soil acidity. Deficient plants are usually found on slightly acid (pH 6.6-7.0) or alkaline soils (pH > 7.0), e.g., lake beds, glacial outwashes, peats and mucks. Acid soils that have been limed are more likely to be manganese deficient than naturally neutral or alkaline soils.
Manganese-deficient organic soils and dark-colored sandy loams usually have a pH greater than 5.8. The pH of deficient mineral soils is usually above 6.5. The mineral soils are usually dark at the surface and have a gray subsoil. Manganese deficiency is seldom found on glacial till or moraine soils.
Field and vegetable crops vary in their response to manganese fertilizer. The degree of response to manganese fertilizer for several crops is given in (Vis. 6). Dry edible beans, cucumbers, lettuce, oats, onions, peas, potatoes, radishes, sorghum, soybeans, snap beans, spinach, Sudan grass, sweet corn, table beets and wheat are the most responsive crops.
Manganese Deficiency Symptoms
Most crops deficient in manganese become yellowish to olive-green. Potatoes show reduced leaf size. Grain crops have a soft, limber growth, which often appears diseased. In oats, this may be described as "gray specks." Wheat (Vis. 13)and barley often show colorless spots. Manganese- deficient corn plants grown on organic soils show light yellow-green pinstriping of the leaves, also described as interveinal chlorosis (Vis. 11). Manganese deficiency in field corn has seldom been observed on mineral soils in Michigan.
Manganese deficiency in soybeans, (Vis. 14), (Vis. 15) dry edible beans, snap beans, sugar beets (Vis. 12), celery (Vis. 8), cucumbers and cabbage(Vis. 9) often causes marked yellowing between the leaf veins; the veins themselves remain dark green (Vis. 7), (Vis. 10). This pattern is similar to iron deficiency but occurs more generally over the plant-iron deficiency is most pronounced on new growth. In sugar beets (Vis. 12)and potatoes, chlorosis begins in the younger leaves. Later, gray and black freckling may develop along the veins.
Manganese-deficient onions are olive-green and the leaves may appear wilted(Vis. 10). Manganese deficiency is sometimes confused with nitrogen deficiency. To separate the two, make a nitrogen tissue test. A tissue test for nitrate N easily determines which nutrient is deficient. Manganese-deficient plants usually test higher than normal in nitrate nitrogen because of the lack of Mn enzymes required to convert nitrate to protein N.
Correcting Manganese Deficiency
Manganese deficiency in crops can be prevented by band applying manganese fertilizer to the soil, spraying it on the foliage or making the soil more acidic. Steam or chemical fumigation will also correct it temporarily. Generally, when manganese is deficient, manganese sulfate or manganous oxide is mixed with the fertilizer and applied in a band near the seed. Commercial manganese sulfate is 26 to 28 percent manganese (Mn); manganous oxide is usually 41 to 68 percent manganese.
Studies have shown that manganous oxide should be finely ground to be effective. Granular manganous oxide (8 mesh) was largely ineffective. Manganous oxide powders (200 and 325 mesh) were less effective than manganese sulfate but were acceptable. These materials do not blend well with other fertilizer materials segregation problems occur because of differences in particle sizes. However, the use of a sticker such as liquid fertilizer has made it possible to use these finely ground materials in the bulk blending process.
Manganic oxide (MnO4), which has been used in Michigan, is insoluble and ineffective as a manganese fertilizer regardless of mesh size. Chelated manganese materials have not performed satisfactorily on organic soils and have been less effective on mineral soils than manganese sulfate.
Broadcast application of manganese is not recommended because of high fixation in the soil. Residual carryover of available manganese fertilizer is usually low. Therefore, manganese must be applied every year on a deficient soil. Suggested rates of application based on soil tests can be found in MSU Extension Bulletins E-550A http://www.msue.msu.edu/msue/imp/modf1/modf1e.html and E-550B. Foliar applications of manganese are recommended when: (1) fertilizer is not applied in a band near the seed,
(2) deficiency symptoms appear on the foliage, or
(3) regular fungicide and insecticide sprays are applied.
The recommended rate is 1 to 2 pounds of manganese per acre in 30 gallons of water, using the 1-pound rate if plants are small and the 2-pound rate if plants are medium to large. Spray grades of the manganese carriers are recommended to prevent nozzle plugging. Some fungicides contain manganese but generally not enough to correct a deficiency.
Acidifying the soil with materials such as sulfur and aluminum sulfate can correct manganese deficiency. These treatments cost more than manganese fertilizers. Acid- forming nitrogen and phosphorus fertilizers promote the release of fixed soil manganese, especially if banded near the plant. Soil around the fertilizer band may be one pH unit more acid than soil farther from the fertilizer band. Some of the benefits accredited to band placement of fertilizer may be due to the release of fixed soil manganese.
Manganese Toxicity
Excessive manganese is a problem in extremely acid soils (< pH 5. 0), especially if the soil is steamed or fumigated. A toxic manganese situation may also develop in plants if excessive soil and/or foliar applications are used. Liming soils to the desired pH range for the crop will usually prevent any manganese toxicity.
In the early stages of plant growth, manganese toxicity symptoms may be similar to deficiency symptoms. The interveinal chlorosis caused by toxicity in soybeans is more distinctive than that caused by deficiency. The typical spotting is followed by scorching on leaf margins and leaf cupping. In potatoes, the symptoms are chlorosis and black specks on the stems and undersides of the leaves, followed by death of the lower leaves.
The following crops are sensitive to excess manganese: alfalfa, cabbage, cauliflower, clover, dry edible beans, potatoes, small grains, sugar beets and tomatoes.
Plant tissue analysis is helpful in diagnosing manganese status. Values below 20 parts per million (ppm) are usually considered deficient. Readings of 30 to 200 ppm are normal, and those over 300 ppm are considered excessive or toxic.
Some growers have experienced plant damage from certain combination pesticide-manganese sulfate sprays. Soybeans and other crops have been damaged when 8 pounds of manganese sulfate per acre was applied by an air-blast sprayer. To prevent extensive damage, growers should always try out a spray program on a limited acreage. Injury is evident within 48 hours after application.
