You know soybeans need inoculant. Some research indicates they also need a calcium-molybdenum dressing for early days in the seed bed. Will seed dressing benefit the 2017 crop in Western Canada?
By John Dietz
Seed inoculant is on the radar, or should be, for virtually every soybean grower in Manitoba in 2017. Just about as important is a seed treatment, to prevent early disease.
Both get lots of advertising and support from agronomists, but there’s more.
Do you know about a third step that dresses the seed with two micronutrients for those early days of germination?
Seed dressings are a nutrient or fertility package, rather than inoculant or protectant.
Applied directly, there is some evidence that “dressed” soybeans can be stronger and healthier in their early growth, can better overcome later stress, and can produce somewhat more yield in some situations.
Seed dressings are not supported by traditional extension research or recommended by associations. They can be liquid or powder. Only a few companies make them.
The scientific basis still is being debated. North Dakota State University, for instance, has failed to find a consistent or significant yield response.
One of the leading suppliers is OMEX Agriculture Inc., Winnipeg. Omex is a liquid fertilizer company that manufactures several seed dressings, including one for soybeans.
According to Dr. Abdel El Hadrami, CEO and research director, OMEX has been in business worldwide for 40 years and retails products in 65 countries. The OMEX center at Oak Bluff, established about 10 years ago, services Canada and the northern United States.
“We specialize in solutions that address stress,” says El Hadrami, a former University of Manitoba scientist in plant pathology.
The OMEX seed dressings offered for soybeans are based on two nutrients, calcium (Ca) and molybdenum (Mo), aiming to produce healthier roots and more nodulation.
Value of calcium
Both calcium and molybdenum are recognized as secondary nutrients for soybeans.
The uptake of calcium by an average soybean crop is higher than for cereals, oilseeds, pulses, or potatoes. Along with dry beans and canola, soybeans also remove more calcium than our other crops.
In early development, with assistance from rhizobia bacteria, soybean roots form the nodules that supply the nitrogen for the crop. However, the bacteria had to be introduced to Prairie soils with the seed.
That process, building a native rhizobium population, still is underway. It is slowed by intervening crops other than soybeans. It also is slowed by cool, wet conditions in the seedbed when soybeans are germinating.
Even if we plant soybeans back to back, the scientist says, we need to inoculate the seed. The bacterial population needs to be present in enough numbers, growing quickly, before the complex nodulation system can be successful.
Typical wet soil conditions limit the air supply, limiting that bacterial growth and reproduction.
Scientists in several countries are working to untangle and explain the process we see as nodule formation, he says.
One is Dr. Allan Downie at the John Innes Center in Norwich, England. Downie’s group has followed the nodulation process and discovered that a calcium-based signal identifies specific bacteria. If the “signal” is right, the root will allow the bacteria to enter and initiate the nodulation process.
Downie spoke to Manitoba producers in 2013 at the invitation of OMEX. Research with calcium, molybdenum, and other micronutrients associated with soybeans is underway in the United States, Brazil, India, and Malaysia.
The point, El Hadrami says, is that rhizobia require both calcium and molybdenum at the right time to successfully infect the soybean root. When they do, the root grows threads where the nitrogen-bearing nodules actually form.
Value of molybdenum
Molybdenum is needed in very tiny amounts, but has a big impact, says the OMEX Canada CEO.
Molybdenum is involved in nitrogen metabolism for soybeans. Without it, he says, the pulse roots cannot nodulate or efficiently utilize nitrogen.
He explains that a two-sided enzyme known as nitrate reductase is what converts nitrogen into the ammonium form that builds root nodules. One side of that enzyme requires a molybdenum-containing ion.
“The structure of the enzyme relies on molybdenum and iron. The iron turns those nodules red. The molybdenum is attached to it. If either is missing, you end up having poor nodulation and nodules that are not functioning,” El Hadrami says.
Molybdenum in our soil is generally adequate, but a few good crops of canola can deplete the supply. The classic symptoms of deficiency in soybeans are poor leaf structure and weak or poor leaf colour.
“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.”
A seed dressing containing both calcium and molybdenum is the first line of defense.
Molybdenum deficiency can be treated even after emergence, he adds. Molybdenum is mobile in both phloem and xylem tissues, so plants respond quickly to foliar applications.
Regulation changes about three years ago has made it easier for dressings to get onto retail shelves in Canada.
“The first time we talked about this concept of putting fertilizer on seed was 2006. The concept is still challenging and new for the majority of the industry, but there is a little improvement in understanding,” the scientist says.
“Seed dressings allow early establishment and good nodulation. In a year that has stress, you definitely can see four to five-bushel yield differences,” El Hadrami says.