The aim of the research was to determine the quantitative and qualitative composition of the communities of fungi and bacteria formed in the soil under the influence of onion cultivation, with consideration to various options of conserving cultivation, using spring rye and common vetch as after-crop cover plants. Moreover, in the laboratory tests, the occurrence of microorganisms characterizing by an antagonistic influence on pathogenic fungi with a facultative parasiting was established. As a result of the laboratory microbiological analysis it was found out that particular soil samples taken from under the cultivation of onion differed with the qualitative and quantitative composition of microorganisms. Spring rye stimulated the growth and development of microorganisms, especially antagonistic ones (Bacillus spp., Pseudomonas spp., Gliocladium spp., Trichoderma spp.), and common vetch caused an increase of the number of cfu of pathogens (Alternaria alternata, Fusarium culmorum, F. oxysporum, F. solani, Penicillium spp., Pythium irregulare).

65-75