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Statistical Evaluation of the Rhizosphere Effect¹

ABSTRACT

The paired t-test was used to analyze the results of a microbiological study of soil on the surface of plant roots and soil apart from the roots. The increase in the numbers of bacteria, actinomycetes, fungi and protozoa in the rhizosphere soil of wheat was highly significant as was the increased incidence of ammonifying and denitrifying bacteria and "radiobacter" types. Anaerobes and aerobic cellulose decomposers were also more abundant on the root surface but not algae, anaerobic cellulose decomposers, spore formers or Azotobacter. Essentially similar results were obtained with barley and soybean plants. The preferential stimulation in the rhizosphere of bacteria requiring amino acids for optimal growth and the relative decrease in the proportion of those requiring factors in yeast and soil extracts were found to be highly significant with the three crops studied. However, the absolute numbers of both these groups of bacteria are higher in the rhizosphere soil.

¹ Contribution No. 489, Microbiology Research Institute, Research Branch, Canada Department of Agriculture, Central Exp. Farm, Ottawa.

² Microbiology Research Institute.

³ Professor and Head of Department of Microbiology, University of Manitoba, Winnipeg.

Received for publication August 19, 1959. Accepted for publication March 1, 1960.