Nodulation and nitrogen fixation of legumes depend on the efficiency of Rhizobia forming root-nodules. In soils with sparse and ineffective population, legumes nodulate poorly and nitrogen fixation is limited under the level of the genetic potential of the plant.
Factors influencing the indigenous soil Rhizobium population are qualitatively rather well-known.
Inoculation of the legumes is one possibility to establish an effective symbiosis for adequate nitrogen fixation. Since Rhizobium is able to persist in soil as a saprophyte without host plant, soil properties and management as well as crop rotation play a significant role to ensure the survival of proper Rhizobia in soil. In acid soils, liming significantly improved nitrogen fixation and growth of the peas already at first year. Since low pH has earlier being demonstrated to select ineffective strains of Rhizobium, liming apparently enabled the more effective strains of the population to proliferate and nodulate the host plant thus leading to improved growth. Results, including the effect of the host plant on the Rhizobium population will be discussed in the presentation.