Influence of different initial soil moisture contents on the distribution and population dynamics of introduced Rhizobium leguminosarum biovar Trifolii

Data on bacterial distribution in soil were obtained with a method of washing and thoroughly shaking of the soil. Bacterial cells attached to or enclosed in different size groups of soil particles or aggregates were separated and enumerated on plates containing selective media. Soil portions of a loamy sand and a silt loam with different initial moisture contents were inoculated with Rhizobium leguminosarum biovar trifolii. Results of this experiment indicated that the initial moisture content influenced the distribution of the inoculated rhizobial cells. Differences in distribution were still found after prolonged incubation periods, suggesting a lack of transport and migration of the rhizobial cells. It was shown that rhizobial cells survived better in soils with a lower, than in soils with a higher initial moisture content. Rhizobial cells attached to or enclosed in soil particles or aggregates larger than approx. 50μm had a more favourable microhabitat than unattached cells or cells attached to smaller particles.