The experiment was conducted in the years 1999–2001. The object of the studies was the rhizosphere soil of soybean ‘Polan’ cv., and 0.1% chitosan. This compound was used once (seed dressing), twice (seed dressing and seedling spraying), three times (seed dressing, seedling spraying and plant spraying at anthesis). The experiment also considered a control combination, i.e. without chitosan. The purpose of the studies was to determine the effect of chitosan on the qualitative and quantitative composition of microorganisms in rhizosphere soil with antagonists distinguished. The microbiological analysis of samples of soybean rhizosphere soil taken from particular experimental combinations pointed to different numbers of bacteria and fungi. The greatest total number of bacteria colonies and the smallest number of fungi colonies were characteristic of the rhizosphere soil of soybean after using chitosan three times. This sample of soil contained the greatest number of bacteria and fungi with antagonistic effect towards plant pathogens.

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