The effect of earthworms Lumbricus rubellus on the total count of microorganisms in soil treated with pendimethalin.

This paper examines the modus in which earthworm Lumbricus rubellus with its activity affects the total count of different physiological groups of microorganisms in soil treated with herbicide pendimethalin. The experiment was carried out in ten glass containers with a soil substrate, whereby one of them was the control one, and each group of three containers was treated with different concentration of pendimethalin. A concentration of pesticide of 5 μl/kg, which is recommended by the declaration, one lower concentration of 3 μl/kg and one higher of 7 μl/kg were used. The number of physiological groups of microorganisms is determined from the three containers treated with different concentrations of pendimethalin 48 hours after the treatment, and from the other three containers 21 days after the treatment. Two days after the application of different concentration of pesticide, a significant statistical decrease was found in the number of fungi and cellulotical microorganisms in soil, while the total number of heterotrophic bacteria as well as microorganisms which participate in different stages of nitrogen metabolism increased. However, 21 days after the treatment a significant decrease in the total number of heterotrophic bacteria in all treated containers comparing to the control one was noticed, where earthworms with their activities partially attenuated the negative effect of pendimethalin on soil bacterial flora. They also had a positive effect on the number of fungi, actinomycetes and cellulolytic microorganisms while the presence of earthworms had no significant influence on the number of aminoautotrophs, oligonitrophils and free-living diazotrophs. It was shown that earthworms with their activities attenuate the negative effect of pendimethalin on bacterial flora, actinomycetes and fungi, which points out to their possible use in processes of bioremediation [ABSTRACT FROM AUTHOR]