Neonicotinoid insecticides effects on soil microbiome on irrigated lands
Abstract
Purpose. To determine the effect of the active substances of neonicotinoid insecticides, such as thiamethoxam, thiacloprid and clothianidin on the soil microbiome under irrigation conditions. Methods. The sampling of soil was carried out on the experimental plots of the State Enterprise “Experimental farm “Brylivske”” IWPaLM NAAN in 2019–2020 in the plots where the hybrid tomato Lampo F 1 was grown. Stationary model experiments were conducted on the basis of the State Enterprise “Central Laboratory of Water and Soil Quality” of the Institute of Water Problems and Land Reclamation of NAAS. The drip irrigation method was simulated. The timing of irrigation of soil samples was determined by tensometric method. Identification, isolation and cultivation of soil microorganisms was carried out according to generally accepted bacteriological methods. To determine the percentage of variation of the studied soil parameters under the influence of different doses of each insecticide, a bidirectional analysis of variance (ANOVA) was performed. The study of the effect on soil microorganisms was carried out with the use of 1-fold 5-fold and 10-fold doses of drugs and with an exposure duration of 1, 14, 28 and 56 days. Results. It was found that with an increase in the dose of clothianidin and the duration of exposure, an increase in colony-forming units (CFU) of phosphate-mobilizing bacteria, bacteria of the genus Azotobacter and immobilizing mineral nitrogen occurs. A negative effect of clothiadin on the CFU count of micromycetes and pedotrophic bacteria was established. In the case of pedotrophic microorganisms, the decrease in the population significantly depended on the combination of dose and duration of drug exposure. Also, the number of colony-forming units of micromycetes decreases depending on the dose and duration of action of thiamethoxam and thiacloprid. Pedotrophic microorganisms and actinomycetes were less sensitive to the action of thiamethoxam, and the duration of action of the drug had a statistically significant effect on the size of their population. Bacteria immobilizing mineral nitrogen with increasing dose and exposure of thiamethoxam and thiacloprid for 14 and 28 days significantly increased the number of CFU. It was revealed that an increase in the dose of thiacloprid and the exposure time has a positive effect on the populations of amonificuval bacteria and the genus Azotobacter. Conclusions. It has been established that an increase in CFU of bacteria immobilizers of mineral nitrogen in the soil under the influence of thiamethoxam, thiacloprid and clothianidin, probably indicates the participation of this group of microorganisms in the biodegradation of the tested neonicotinoid insecticides. Soil microorganisms belonging to mycromycetes were the most sensitive to the action of the studied pesticides under irrigation conditions.
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