Nodules form when Rhizobium bacteria penetrate root hairs, causing the gall-like structures that house the bacteria. The plant and bacteria then work together, mutually benefiting one another. The bacteria supply nitrogen to the plant, and the plant supplies carbohydrates to the bacteria. The amount of nitrogen supplied to the plant depends on the type of Rhizobium that coexists with the plant, and the number of Rhizobia that penetrate the root hairs. In natural systems, the type and amount of Rhizobia in the soil is often not ideal for the crop.
Inoculants therefore have two functions.
Firstly, they provide the best type of Rhizobium bacteria for maximizing nitrogen fixation by the crop, and secondly, they supply the ideal concentration of Rhizobium surrounding the seed to ensure optimum nodule formation. Byron Irvine of the Brandon Research Centre and Guy Lafond of the research farm at Indian Head, Saskatchewan, say that soybean producers commonly use this method to provide the most effective strains of nitrogen-fixing bacteria, or rhizobia. However, similar information on delivery and dose has not been available for field pea production.