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Assessing Nodulation

Posted: Jun 11, 2021

With Ignacio Crippa and Rene Mabon

Nodulation is when new organs called nodules are formed near the roots of pulse crops like peas, lentils, soybeans and chickpeas. These nodules fix nitrogen that’s present in the air and supply it to the plant in a form that it can use in a process known as nitrogen fixation.

Not sure the proper way to assess nodulation and nitrogen fixation with your legume crops? Rene Mabon, Agronomic Services Manager with BrettYoung, and Ignacio Crippa, Technical Service Leader for Rizobacter, are here to help.

When does Nodulation Typically Occur in Western Canada?

Nodulation normally occurs fairly early in plant development. You’ll typically begin to see small nodules within 15 days of emergence if environmental conditions are adequate, but if the plants are under stress, they can delay nodule development as they attempt to conserve their energy and resources.

Mabon says that the best time for you to assess nodulation in a crop is at the start of the reproductive stage, soon after flowering begins. By assessing early, there will still be time to identify and address nutrient deficiencies.

He cautions, however, not to start your assessment too soon, since nodules may not yet be visible. In the case of soybeans, he recommends conducting a second assessment later in the reproductive stage to ensure nitrogen is being provided for the greatest period of requirement of the crop.

How do you Check for Nodules?

Mabon suggests using a shovel to carefully dig up a sample plant. You will likely need to soak the plant’s roots in a bucket of water to loosen soil without pulling off any nodules. When it comes to soybeans, healthy nodulation is indicated by the presence of eight to 12 nodules on the main stem or taproot of each plant. When it comes to peas, you are looking for three to five clusters of nodules per plant.

“If you’re only seeing one or two per plant, alarm bells should be going off,” he adds.

Does the Size of the Nodule Matter?

Size does matter when it comes to nodules, according to Ignacio Crippa. Nodules, Crippa explains, should be at least three millimetres in size in early evaluations and distributed evenly near the plant’s root.

We are often asked which is better between a lot of small nodules or a few large ones, but our research comparing total nodule weight to the number of nodules present on a plant indicates that a few larger nodules can be just as effective as a larger number of small nodules.

Nodule location can depend on the type of inoculants that you are using. Nodules tend to be concentrated near the plant’s main root when you use seed-applied inoculant, and they can be more spread out when you use granular products.

How can you Tell if the Nodule is Working?

Split it in half and check the colour, Crippa says. If it’s reddish in appearance, that means the nodule is working. If it is green, that means that it fixed nitrogen at one point but isn’t doing so anymore. If the nodule is green or white, it isn't fixing nitrogen.

BrettYoung and Rizobacter Biologicals

BrettYoung offers a number of different biological products that help promote nitrogen fixation and nodulation, including Signum Soybean, a seed treatment with Bio-Inducer Technology that Rizobacter developed, and Osmium, a liquid inoculant for peas, lentils and chickpeas. Both include Osmo-Protector technology that helps make the bacteria (Rhizobium) in the plants tougher and better-equipped to handle environmental stresses.

Mabon says that it’s important for growers to think about timing when it comes to applying any kind of on-seed products, since it can potentially impact nodulation.

“One of the things that I think people often forget,” Mabon explains, “is even though Rizobacter inoculants provide significantly improved on-seed life, the closer you do your inoculation to seeding time, the better off you are with any of the on-seed products.”

The number of live bacteria you put down in the ground with the seed does matter, too.

“When you apply it to the seed or with seed treatments, or if you leave it to sit for too long, those numbers go down. The closer you can do it to seeding time, the better off you are going to be.”

To learn more about BrettYoung’s inoculants, visit our biologicals page. If you would like more help with selecting inoculants or need a more customized recommendation for your farm, contact your BrettYoung Regional Account Manager.

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