The impact of glyphosate herbicides on soil microbial activity from the Carajás National Forest

The objective of this study was to evaluate the impact of different glyphosate‑based herbicide formulations on microbial activity of soils from Carajás National Forest. We tested three formulations of glyphosate, i.e., Roundup Original®, Roundup Ultra® and Roundup WG® that were applied in five doses: 0; 240; 480; 720 and 1440 g of active ingredient in acid equivalent ha-1, with four replications. Herbicides were sprayed on pots containing 500 g of soil derived from the 0-10 cm layer of the study site. We determined the carbon from microbial biomass (C-MB), microbial respiration rate (MR) and metabolic quotient (qCO2) at one and 28 days after herbicide application. No treatment affected the C-MB and MR at one and 28 days of incubation. There was no difference for qCO2 at any dose of Roundup Ultra® and WG® formulations at one and 28 days of incubation. However, the qCO2 was inhibited by the Roundup Original® at one day post treatment. This parameter was normalized at 28 days after herbicide application. The data indicate that no one of the treatments tested cause significant impact on soil microorganisms of the Carajás National Forest, suggesting that herbicide-based invasive weed control could be used