Sulfonylureic herbicide influence on bacterial communities in soil

Abstract

Herbicide use in agriculture may lead to both quantitative and qualitative changes in soil microorganism communities. An experiment was set up to evaluate the influence of two herbicides on microbial processes from soil. Soil for the experiment was taken from field sites of Plant Breeding discipline from the U.S.A.M.V.B. Timisoara. The soil was sifted through a 2-mm sieve and placed in polyethylene bags. Doses of herbicides were prepared with distilled water and applied on the soil samples. Soil samples were incubated at 28°C for 7 days; afterwards the main groups of bacteria involved in nitrogen cycle (nitrogen-fixing bacteria, ammonifying, nitrifying, and denitrifying bacteria) were determined. Tribenuron-metyl and nicosulfuron have a major toxic effect on nitrogen-fixing aerobic bacteria, causing their death in experimental variants using high concentrations. Ammonifying bacteria are sensitive to tribenuron-methyl and nicosulfuron, decreasing numerically with the increasing herbicide dose. Nitrifying bacteria are the most important ecophysiological group for the determination of the toxic effect of the two herbicides in the analysed soil samples.