Inoculating legume seeds key to successful forage stand
Legumes grow in partnership with bacteria called rhizobium to help feed themselves nitrogen, but having the right bacteria matched for each legume species is essential to gaining a good forage stand.
Species of the legume family, which includes peas, beans, vetches, alfalfa and clovers and others have the ability to convert nitrogen from the air into a usable form for the plant to grow, but to do so the seeds need bacteria in the soil. This bacterium is called rhizobium.
“Legumes are interesting in that they are able to ‘fix’ nitrogen,” said Dirk Philipp, assistant professor of forages for the University of Arkansas System Division of Agriculture. “This way we do not have to apply nitrogen fertilizer to forage legumes, resulting in a cost savings.”
Rhizobia bacteria grow into the root hairs of the legume plants and develop nodules. This arrangement allows the bacteria to tap into a source of carbohydrates while providing the plant with nitrogen. If the soil doesn’t have enough bacteria, the plant can’t fix nitrogen. This is where seed inoculation comes in.
“Legume seeds can be coated with water-soluble clay that has the rhizobium in it,” Philipp said. “Luckily, many seeds today come pre-inoculated. The good news is that producers don’t have to worry about inoculating certain species anymore, but the bad news is some plant-specific inoculants are hard to come by for seeds that still require inoculation.”
Without inoculation, the legume plants have to rely solely on available soil nitrogen. If there is not enough—or any—the plants won’t fix the nitrogen and won’t increase the nitrogen that can be recycled back into the soil, which is beneficial to other crops.
In order to insure good nitrogen fixation by the legume, it is necessary to inoculate the legume with the proper strains of bacteria prior to planting the seeds. This simple, low-cost process has many benefits for little cost. In fact, some legumes can fix up to 300 pounds of nitrogen per acre, which enriches the soil and assists other plants in healthy growth.
To inoculate seeds that are not coated with appropriate bacteria, keep these steps in mind.
The inoculant is sensitive to light and high temperatures. To maintain its effectiveness, inoculate legume seeds one or two nights before planting in a relatively dark and dry area, such as a corner of a barn.
Dampen the seeds so the inoculant, which is usually a black powder, will stick to them. The ideal moisture is reached when seeds stick to the hand.
In a bucket, pour inoculant over the seeds little by little while mixing continuously. The seeds will blacken over time through the adhesion of the powder.
Pour the inoculant-covered seeds carefully and evenly onto a large tarp to dry. The seeds should be entirely dry before placing them into the seeder for planting.
Use the seeds within 24 hours after being inoculated.
Check plants roots the next spring to see if nodules are present.
For more information about seed inoculation, visit www.uaex.edu or contact your county Extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.