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Inoculation is the process of applying commercially available rhizobial bacteria to legume seed or into the soil where legume crops—soybeans, peanuts, alfalfa, peas and lentils—will be planted. Rhizobia are the active ingredient in all legume inoculant products. The presence of rhizobia is necessary for a legume to be able to convert atmospheric nitrogen into a usable form in the absence of readily available nitrogen from fertilizers or manure. This process is referred to as nitrogen fixation.
BENEFITS OF INOCULANTS
It’s important for seed companies to inform farmers about the multiple benefits of using nitrogen-fixing rhizobia, including improved crop performance, reduced production costs and reduced greenhouse emissions associated with the production of synthetic nitrogen fertilizers.
Due to the nitrogen-fixing ability of legumes inoculated with rhizobia, the need for commercial nitrogen fertilizer for legume crops is virtually eliminated.
All legume crops produce more yield per acre when properly nodulated, and thus inoculants increase crop income. Jim Beuerlein, professor of agronomy and soybean research and extension specialist for Ohio State University, has evaluated soybean inoculants in hundreds of field trials over the past 15 years. Those trials have shown that inoculation generates an average yield increase of nearly two bushels per acre. “Oftentimes inoculants are dismissed because a two-bushel increase over a 50- to 60-bushel yield isn’t considered to be statistically significant. But that two-bushel increase—generated with a nominal investment—is very economically significant. The fact is inoculation does work, and it has proven itself to be very profitable in the real world.”
Studies of soybeans in soil thought to not need inoculant have shown an increased profit of $5-$15 per acre. On fields where inoculation is needed, increased profit can range from $20-$80 per acre.
With inoculant—numerous nitrogen-fixing nodules formed.
Credit: Becker Underwood
Without inoculant—no root nodules formed.
Credit: Becker Underwood
WHEN SHOULD GROWERS INOCULATE?
When it comes to producing legumes, the question many growers will have is, “When should I inoculate?” While the short answer to give them is, “every year,” several factors are combining to make the coming years particularly compelling for growers to consider incorporating inoculants into their production regimens.
- The last few years have seen record soybean plantings in the United States and it has been predicted acres will continue to rise. Many of these soybeans will be planted into either CRP acres or fields that have been in continuous corn for several years. In either instance, these soils typically have depleted rhizobia populations.
- Many regions of the United States have experienced flooding the last couple years. Flooding results in anaerobic conditions in the soil that can kill native rhizobia. A rhizobial inoculant is critical for proper nodulation in legumes planted into wet soil.
- While rhizobia can stay in the soil for some time, there is no way to effectively test to determine if the rhizobia in the soil are specific to the legume crop being planted, and if they are in sufficient quantities to effectively nodulate the crop.
- Native rhizobia have a tendency to become less vigorous, or lazy, over time. Applying an inoculants helps ensure that fresh, vigorous rhizobia are present and ready to move into the roots to multiply, nodulate and begin fixing nitrogen.
- While native rhizobia have proven survivability, there’s no doubt that commercial inoculants contain the most effective strains in terms of nitrogen fixation.
Source: Becker Underwood
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