Cultural practices, such as herbicide application, can directly interfere with microbial communities of soil and roots. These effects are complex and difficult to be detected, especially when analyzed by conventional methods. On the other hand, the recent development and use of molecular, DNA-based methods allows for a more accurate evaluation of these, often negative, effects. The purpose of this study was to assess the effects of glyphosate and imazaquin-based herbicides, widely used in Brazil, on soil microbial biomass carbon, soil basal respiration and metabolic quotient, and on microbial community associated to rhizoplane of soybean roots. A greenhouse experiment was conducted using soil from a soybean plantation treated with constant applications of these herbicides. Soil microbial biomass carbon, basal soil respiration and metabolic quotient were determined before herbicide application and 2, 14, 30, and 62 days afterwards. The bacterial community associated to rhizoplane was analyzed by Denaturing Gradient Gel Electrophoresis (DGGE) and Ribossomal Interspacer Analysis (RISA) 14, 30 and 62 days after herbicide application. Results indicated no significant changes in soil microbial biomass carbon, basal respiration and metabolic quotient as a result of the herbicides application. However, both herbicides changed the bacterial profile in the rhizoplane during the experimental period. DGGE and RISA analysis detected absence, as well as presence of some bacteria in the herbicide treatment compared to the control. The bacterial profile similarity between the herbicide treatment and control was less than 55 % in all periods analyzed.
herbicides; DGGE; RISA; microbial biomass carbon; soil basal respiration; metabolic quotient
