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RESEARCH PRODUCT

Effects of dimethoate and benomyl on soil organisms and soil processes – a microcosm study

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Abstract Effects of two pesticides, dimethoate, an insecticide, and benomyl, a fungicide, applied singly or together, on soil organisms and plant growth were studied in microcosms containing agricultural soil and indigenous soil fauna together with introduced invertebrates and barley. Dimethoate reduced soil microarthropod populations and the reduction was stronger in the upper than in the lower soil layer. The collembolan community structure was affected by both pesticides. Populations of microarthropods in pesticide-treated microcosms recovered during the experiment but the community structures remained differentiated. Total numbers of enchytraeids and nematodes were not affected by either of the pesticides. The pesticides affected microbial biomass (ATP content) to some extent, but did not affect CO 2 production, soil mineral N or barley growth. It can be concluded that although pesticides had transient effects on microorganisms and, possibly, some microbivorous animals, their influence on nutrient dynamics was negligible and they did not affect plant growth indirectly.