Selecting the specific Rhizobia for each legume
Rhizobia bacteria are not all alike. In general, each type of legume requires its own specific
strain of Rhizobia to nodulate and fix nitrogen. For example, those that will effectively
nodulate soybeans are unable to cause nodules to form on alfalfa. Scientists have identified
thousands of strains of Rhizobia bacteria, each possessing some unique characteristics. For
optimal results, the inoculant strain needs to be specific to the plant, and even among
effective strains, some will work better than others. However, one strain is appropriate for
both peas and lentils.
Certain strains of bacteria produce nodules that provide little or no benefit to plant growth.
Native strains in soils are often of this type. The process for selecting new and better strains
requires the isolation of a Rhizobial strain from a nodule and then testing its ability to fix nitrogen.
EMD Crop BioScience currently maintains a collection of thousands of strains of Rhizobia. We continually
test strains in order to select those with the greatest nitrogen-fixing capability.
Inoculant formulations
- Liquid inoculants represent the newest advance in inoculant technology. They may be
applied directly to the seed, in-furrow, or dealer-applied, depending on the crop. Liquids
are easy to use and have consistently demonstrated superior performance.
- Granular peat inoculants are used to apply the inoculum in a seed furrow through
insecticide hoppers on planters, or with air seeders. Granular materials generally deliver
higher Rhizobia numbers than seed-applied peat products.
- Peat-based powders applied to the seed in the hopper box were the first carriers for the
inoculant. A new form is sterile powder, in which the peat is sterilized by gamma radiation
before adding the Rhizobia. This process extends the product shelf life and increases
Rhizobia concentrations.
EMD Crop BioScience®, which commercialized inoculants in
North America, first used peat powders as carriers for the inoculant. This concept was copied
by other inoculant manufacturers. EMD Crop BioScience brand inoculants have been at the forefront in the
development and use of liquid carriers.
Methods of inoculation
Inoculants can be either seed-applied or used in-furrow. Using powder on-seed is the oldest
method, while in-furrow methods became common with the development of granular
products. Recently the development of liquid inoculants has further increased the
application options available to the grower.
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Peat-based powder is applied to seed in the hopper box.
Granular products made with peat provide an ideal environment for bacteria to live. They are applied in-furrow.
Liquid inoculants are relatively new. They offer ease-of-use and flexibility with application methods - some liquids are applied on-seed, some are applied in-furrow, and some can be applied both ways.
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