A b s t r a c t. The effect of chemicals (Reglone 200 SL and Elastiq 550 EC) on soil microorganisms and their enzymatic activity was estimated. The study was conducted in a field experiment which was set up in the split-block design and comprised three treatments. Soil samples were taken six times, twice in each year of study. The results showed that the application of chemicals generally had no negative effect on the number of soil microorganisms. The application of Reglone 200 SL caused an increase of proteolytic and ureolytic activity and affected the activity of dehydrogenases, acid and alkaline phosphatases in the soil. The soil subjected of Elastiq 550 EC was characterized by lower activity of dehydrogenases, protease, urease and alkaline phosphatase.K e y w o r d s: soil, microorganisms, enzyme activity, Reglone 200 SL, Elastiq 550 EC

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Plant protection agents applied in agriculture deserve special attention, given their toxicity, accumulability, and persistence in the soil environment, where they frequently induce disturbances in biochemical processes. Assessment of the risk associated with introduction of chemical preparations to agricultural cultivation is an essential element of protection of the natural environment against the harmful effects of these substances. Therefore, a three-year field study (2010 to 2012) was carried out to assess the long-term effect of soil contamination with the Reglone 200 SL herbicide and Elastiq 550 EC preparation (limiting rapeseed loss) on the course of the ammonification and nitrification processes and soil respiratory activity. The experiment was established in the split-block design on soil classified as black earth proper (WRB-Mollic Gleysols) with pH= 6.1. Soil for the analyses was sampled in 8 periods, that is, after 2, 10, 12, 14, 22, 24, and 26 months of the experiment. The experiments demonstrated that the amount of emitted CO 2 and the content of ammonium and nitrate ions depended largely on the period of the analysis and the type of the chemical agent. The optimal dose of 200 SL and Elastiq 550 EC applied caused periodic statistically significant changes in the respiratory activity and the intensity of the ammonification and nitrification processes in the tested soil.