Dynamics of the microorganisms’ number in the soil mass of podzolized chernozem after treatment with fungicides of various origins

Abstract

In a laboratory model experiment, the dynamics of the number of bacteria and micromycetes in the soil mass of podzolized chernozem after a one-time treatment of its surface with fungicides of various origins investigated. Chemical fungicides based on the active substances carbendazim, tebuconazole and azoxystrobin, and biological fungicides based on the antagonistic fungi Trichoderma viride (lignorum) and Chaetomium cohliodes were used. The soil mass for the experiment was taken from the arable layer of the soil on the site without fertilizers in the field experiment of the Department of Agrochemistry NSC "Institute for Soil Science and Agrochemistry Research named after O. N. Sokolovsky" (NSC "ISSAR") on the territory of SE "EF Hrakivske" (Noviy Korotych village, Kharkiv district, Kharkiv region). During 110 days of composting at a constant temperature, changes in the state of microbial communities, in particular soil micromycetes, and the speed and completeness of their recovery compared to soil not treated with fungicides evaluated. The state of the microflora was monitored four times during the study period according to the parameters of the number of microorganisms belonging to various ecological-trophic and taxonomic groups, the total biological index (TBI) and indicators reflecting the functional state of microbial coenoses (oligotrophy and mineralization indices, the coefficient of microbial transformation of soil organic matter (MTSOM). On the fifth day after treatment with fungicides, the number of bacteria and micromycetes in the samples of the treated soil mass was slightly higher higher than in the control samples, and on the twentieth day, on the contrary, it was significantly lower. The number of bacteria was lower by 20-46 %, micromycetes by 16-34 % compared to the control. On the fortieth day, a partial restoration of the number of bacteria to the level of the untreated control soil observed, and the number of micromycetes remained lower by 9-36 % compared to the control in the case of chemical fungicides. When using biological fungicides, the number of micromycetes approached the values in control soil and accounted for 84-94 % of them. On the one hundred and tenth day, the number of microflora in the soil treated with chemical fungicides according to TBI was 79-89 % of the control values, and in the soil treated with biofungicides it was 102-104 %. The number of micromycetes decreased to a lesser extent and recovered most completely and quickly in the case of the application of the biological fungicide Hetomic. Given the important role of soil micromycetes in the functioning of soils, a decrease in their number due to the accumulation of residual amounts of chemical fungicides in the soil can have a negative impact on many soil-biological processes, in particular the decomposition of plant residues and further transformation of organic matter, as well as on the phytosanitary state of the soil. Therefore, in order to avoid the possible consequences of their excessive or repeated application and the associated threat of soil contamination, it is necessary to carry out microbiological monitoring of soils in areas with a high fungicide load.