Molybdenum (Mo) is a trace element found in the soil and is required for the synthesis and activity of the enzyme nitrate reductase. Molybdenum is vital for the process of symbiotic nitrogen (N) fixation by Rhizobia bacteria in legume root modules. Considering Mo’s importance in optimizing plant growth, it’s fortunate that Mo deficiencies are relatively rare in most agricultural cropping areas.

Quick Facts

Molybdenum-deficiency symptoms show up as a general yellowing and stunting of the plant. A Mo deficiency can also cause marginal scorching and cupping or rolling of leaves.

Quick Facts

Several materials supply Mo and can be mixed with nitrogen (N), phosphorus (P) and potassium (K) fertilizers applied as foliar sprays or used as a seed treatment. Seed treatment is the most common way of correcting Mo deficency because of the very small amounts of the nutrient required.

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Plants take up Mo as the MoO42- anion.

Quick Facts

Molybdenum becomes more available as soil pH goes up, the opposite of most other micronutrients

Quick Facts

Excessive Mo is toxic, especially to grazing animals.

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Molybdenum (Mo) is a trace element found in the soil, and is required for the synthesis and activity of the enzyme nitrate reductase. Molybdenum is vital for the process of symbiotic nitrogen (N) fixation by Rhizobia bacteria in legume root modules. Considering molybdenum’s importance in optimizing plant growth, it's fortunate that Mo deficiencies are relatively rare in most agricultural cropping areas.

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Plants take up molybdenum (Mo) as the MoO42- anion. It’s required for the synthesis and activity of the enzyme nitrate reductase and. vital for the process of symbiotic nitrogen (N) fixation by Rhizobia bacteria in root nodules. It’s also needed to convert inorganic phosphorus (P) to organic forms in the plant.

Molybdenum deficiencies show up as general yellowing or stunting of the plant, and more specifically in the marginal scorching and cupping or rolling of leaves. An Mo deficiency can also cause N-deficiency symptoms in legume crops such as soybeans and alfalfa, because soil bacteria growing symbiotically in legume root nodules must have Mo to help fix N from the air.

Molybdenum deficiencies occur mainly in acidic, sandy soils in humid regions. Sandy soils, in particular, more typically lack Mo than finer-textured soils. Molybdenum becomes more available as soil pH goes up, the opposite of other micronutrients. Since Mo becomes more available with increasing pH, liming will correct a deficiency if soil contains enough of the nutrient. However, seed treatment is the most common way of correcting Mo deficiency because only very small amounts of the nutrient are required.

Heavy P applications increase Mo uptake by plants, while heavy sulfur (S) applications decrease Mo uptake. Applying heavy amounts of S-containing fertilizer on soils with a borderline Mo level may induce Mo deficiency.

Excessive Mo is toxic, especially to grazing animals. Cattle eating forage with excessive Mo content may develop severe diarrhea.

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Source: Soil Fertility Manual (2006) by the International Plant Nutrition Institute (IPNI) and the Foundation for Agronomic Research (FAR).

Deficiency Symptoms

Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.

All photos are provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection. The photos above are a sample of a greater collection, which provides a comprehensive sampling of hundreds of classic cases of crop deficiency from research plots and farm fields located around the world. For access to the full collection, you can visit IPNI's website.