This work aimed to evaluate the impact of glyphosate, imazaquin and trifluralin on soil microbial biomass, on bacteria community associated with soybean rhizoplane and soybean nodulation under two different agricultural management: no-tillage (SD) and conventional tillage (SC). The results showed that imazaquin in SD area lead a significant reduction of soil microbial biomass during the period of evaluation (60 days) and, also had greater modifications in bacterial DGGE profile than the glyphosate treatment. There was no significant effect of herbicides on microbial biomass in SC area, and DGGE profiles presented high variability among replicates of the same treatments, which had difficult the observation of herbicides effects. Some fragments excised from DGGE gels and sequenced indicate that glyphosate interfered in the development of a bacterium with 90% of homology to Herbaspirillum sp. 16S rDNA, while another with 96% of homology to Ralstonia sp. 16S rDNA was greatly present only in imazaquin treatment, and some others bacteria with more than 92% of homology like Burkholderia, Thiomonas and Pseudomonas were not affected by herbicides. Besides that, no significant effect of the herbicides occurred on soybean nodulation.
Microbial biomass; glyphosate; imazaquin; trifluralin; DGGE