Soybean School: Managing manganese deficiency

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In 2019, many Ontario soybean fields showed signs of severe manganese deficiency.

Many of the problem areas were a direct result of growing conditions that featured both soil temperature and moisture extremes, says AGRIS Co-operative agronomist Dale Cowan, who notes that many soils in southwestern Ontario tend to be naturally low in manganese. Any time the growing season brings additional stresses, it tends to accentuate the problem, he adds.

On this episode of RealAgriculture’s Soybean School, Cowan explains why manganese is often unavailable in the soil and offers tips on how growers can identify plants and fields suffering from the micronutrient deficiency. In soybeans, symptoms always occur in new growth. These include distinctive green veins with the rest of the leaf blade turning yellow or a pale green.

In extreme cases, growers can see a significant yield impact. Field research indicates manganese deficiency can deliver a five to 10 bu/ac yield hit. Cowan has seen test plots where yield loss reached 26 bu/ac.

Foliar feeding of manganese is the best management option in-season. In the video, Cowan notes that two or more applications may be required. He also discusses application rates for different foliar products. (Story continues after the video.)

For long-term management solutions, Cowan says it’s important to pay attention to soil tests. Many areas of southwestern Ontario typically see lower soil pH levels, which contribute to manganese deficiency. He notes it’s important for growers to maintain optimum pH levels, but they must be careful not to “over lime” because when pH levels are too high manganese availability is lower, too.

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