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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)

Other Factors Affecting Nitrogen Fixation

Rhizobia bacteria require the availability of molybdenum (Mo), a soil element. In Pennsylvania, Mo is generally present in soils in sufficient quantity, but its availability is affected greatly by the soil pH. Soil into which a legume is being planted should be limed to raise the pH to between 6.5 and 7.0.

Some inoculants or preinoculated seed maybe sold with combinations of Mo and or a fungicide. These additional treatments tend to reduce the number of live Rhizobia and generally are not recommended.

When establishing forage legumes, 20 pounds of nitrogen per acre is often recommended as a starter application. However, if conditions at planting are favorable for quick seed germination and seed has been inoculated, this starter nitrogen fertilizer is often unnecessary.

Do not apply nitrogen fertilizer to established legumes. Legumes can fix all the nitrogen they need for growth. Research has shown that nitrogen fertilizer does not increase yield of established legumes if the plants are effectively nodulated. In fact, fertilizer nitrogen discourages nodulation and inhibits nitrogen fixation.