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Topics : Successful Forage Establishment : Inoculation of Legumes for Maximum Nitrogen Fixation

Inoculation of Legumes for Maximum Nitrogen Fixation

Additional inoculation information via the Forage Information System (FIS)


Inoculant is Species Specific

Legumes have the ability to form a mutually beneficial (symbiotic) relationship with certain soil bacteria of the type or genus Rhizobia. The benefit to the plant, and thus to the grower, is that these bacteria can take (fix) nitrogen from the air (in soil spaces) and make it available to the plant via symbiotic nitrogen fixation. The amount of nitrogen fixed can meet the needs of the plant and leave nitrogen in the soil for following crops.

The genus Rhizobia is divided into various species and subdivided into multiple strains. Rhizobia bacteria are fairly specific as to which legumes they will infect, form nodules on the roots of, and for which they will fix nitrogen. Some common legume fspecies followed by the Rhizobia species which can infect them are: Alfalfa and sweetclover = R. meliloti; True clovers = R. trifolii; Peas and vetch (true) = R. leguminosarum; Soybean = R. japonicum; Birdsfoot trefoil = R. loti; and Crownvetch = R. spp.. The specific bacteria to nodulate the legume you are planting may be present in the soil, especially if that legume has been previously grown in the same field. However, to ensure the availability of the correct species and an effective strain of that species, inoculation - adding the bacteria - is practiced. Inoculation is recommended when the legume being planted has not been grown in that field in the past three years or with every planting of a high value crop. Because inoculant is inexpensive and easy to apply, it is good insurance of proper nodulation and nitrogen availability. But be sure to buy an inoculant specific for the legume you are planting.