This study evaluated the effect of the herbicides fluazifop-p-butyl and fomesafen in five concentrations (0.0; 1.05; 2.10; 4.20 and 8.40 µg g-1) and their mixture (Robust®) on microbial activity in soil submitted to no-tillage system (NTS) and conventional planting system (CPS). Samples in Erlenmeyer of 250 mL were treated with herbicide and wetted to field capacity. After every four days, microbial respiration was quantified through CO2 left by the soil. Metabolic quotient (qCO2) and carbon of microbial biomass (CMB) were determined 20 days after incubation. Under NTS, microbial activity increased with fluazifop-p-butyl and decreased with up to 4.20 µg g-1 of fomesafen. Herbicide effect on soil microbial respiration and CMB under CPS was below that observed under NTS.CMB increased with the increase of fluazifop-p-butyl concentration and decrease of fomesafen concentration. The mixture (Robust®) did not influence CMB under NTS, but it was reduced under CPS in higher concentrations. Under NTS, qCO2 increased with the herbicide concentrations, without, however, varying between them. Under CPS, herbicide mixture provided a higher qCO2. In general, the herbicides provided a negative effect on microbial biomass, proportional to the concentrations applied, being smaller in soil under NTS than in soil under CPS.
microbial biomass; fluazifop-butyl; fomesafen; metabolic quotient
