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Molybdenum and calcium for soybeans

It has been said that there are benefits to applying molybdenum and calcium to soybeans prior to seeding. What are these benefits?       

By John Dietz


You know about seed inoculant for soybeans. You know about seed treatment for soybeans. Do you know about seed dressings for soybeans?

For treatments and dressings, it’s the difference between protecting and feeding. Ideally, the seed has all it needs. In reality, it may need protection from diseases, or it may need to draw on some extra nutrients that aren’t readily available beside the roots.

Dressings are the nutrient or fertility packages applied directly onto seed, or as foliar sprays. Advocates say that plants can be stronger, healthier in the early stages, can have some recovery at later stages, and may have improved yields in some situations.

Dressings can be liquid or powder. A few companies make them, but they are not supported by traditional extension research.

North Dakota State University, for instance, has done field research with several products containing secondary or micronutrients. According to Greg Endres, NDSU agronomist, Carrington, the university has failed to find any dressing-type products that provide a consistent or significant yield response.

However, the products continue to be developed, available at farm retailers, and used by growers.

Seed dressings offered for soybeans are based on two nutrients, calcium (Ca) and molybdenum (Mo).


Value of calcium

Soybeans use calcium to build cell walls, to grow roots and shoots. Soil usually has enough calcium. Deficiency symptoms include poor nodulation, poor root growth, stunting, and cracked tissues.

“The majority of our soils in the Dakotas and Manitoba are good for soybeans, but we do have areas in the Dakotas and Nebraska that are really challenged for calcium availability. Then you have poor establishment of the soybeans,” says Abdel El Hadrami, CEO and research director for OMEX, manufacturer of dressings for soybeans, serving Canada, the Dakotas, and Minnesota.

When early spring soil temperature is cold, the microorganisms that normally mineralize calcium for intake by plant roots may be inactive. A possible solution to that is a seed dressing that has a combination of calcium and molybdenum to feed the early root system.

The impact of calcium, El Hadrami says, is seen in early crop establishment and in days to maturity.

“The correlation to yield depends on how well one preserves the early establishment. If you do nothing about a cold snap after the crop is very well established, for instance, the early advantage can be wiped out,” he says.


Value of molybdenum

Molybdenum is involved in nitrogen metabolism for soybeans. Without it, he says, a pulse crop cannot nodulate or efficiently utilize nitrogen.

The key enzyme for converting nitrogen from nitrate into ammonium form for building the nitrogen-supplying nodules is a two-sided enzyme known as nitrate reductase. One side of the enzyme requires a molybdenum-containing ion.

The molybdenum is needed in very tiny amounts, but has a big impact, El Hadrami says.

“When you analyze the structure of the enzyme, it relies on molybdenum and iron. The iron turns those nodules red. The molybdenum is attached to it. If either one is missing, you end up having poor nodulation and nodules that are not functioning,” he says.

The molybdenum supply native to our soil is generally adequate but large amounts can be removed by high bushel crops. A few good crops can deplete the reservoir, he says. Canola is the heaviest consumer of molybdenum in Western Canada.

Molybdenum deficiency in soybeans has two classic symptoms: poor leaf structure and weak or poor color.

“The nitrate reductase makes up about 70 percent of the leaf structure,” El Hadrami says. “If it’s not functioning properly, you have pale, curling leaves with no real structure.”

It’s not too late when you see symptoms in the crop, after first, he says. Plants respond quickly to foliar applications of molybdenum even after symptoms have appeared. Molybdenum is mobile in both phloem and xylem. However, he recommends an in-furrow treatment.

“It brings good nodulation and helps mitigate deficiency early. In acidic soils you wouldn’t grow a pulse or soybeans without molybdenum (i.e., Brazil),” he says.


More acceptance

Competitors in the seed dressing business have increased over the past ten or so years. Regulation changes about three years ago made it easier for dressings to get onto retail shelves.

“The first time we talked about this concept of putting fertilizer on the seed was 2006. The concept is still challenging and new for the majority of the industry, but there is a little improvement in understanding from the farming community,” the scientist says.

Of the two, molybdenum is newer. Tissue tests for molybdenum have been available for only two or three years.

You apply very little on the seed, and you expect a yield increase of five to ten bushels. It’s not always a straight correlation like that.

“It allows an early establishment and good nodulation but, if you don’t mitigate stress that comes later, then the checks will catch up to the treated area. In a year that has stress, you definitely see those 4 to 5 bushel differences,” he says.