Book of Abstracts
11th IFOAM
Scientific Conference
11-15 August 1996
Copenhagen, Denmark

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Indigenous Rhizobium Population in Soil S11

Leinonen, P.

Agricultural research centre, Partala research station for ecological agriculture, FIN-51900 Juva, Finland.

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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. Possible early cultivation of the host plant, pH, temperature extremes and eventual toxic elements (e.g. aluminium) have been found to explain the indigenous population size and efficiency.

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 a two-year pot experiment, I studied the effect of inoculation, liming and host plant on the soil population of Rhizobia nodulating common pea (Pisum sativum). 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.