Growth regulator herbicides and adjuvants effects on soil microbial activity.

Soil microorganisms are vital for maintaining ecosystem functioning and play a central role in the degradation of herbicides. However, the specific effects of herbicides and their formulations on soil microbial activity remain insufficiently characterized, particularly in non-agricultural environments. This study evaluated the impact of five herbicides-Arsenal® (imazapyr), Dominum® (aminopyralid, and fluroxypyr), Pluris® (triclopyr, picloram, and aminopyralid), Garlon® (tricloplyr), and Glyphosate® (glyphosate)-and five adjuvants-Agral, Assist, Aureo, Silwet, and VegetOil-on microbial activity, using global heterotrophic soil respiration as a functional indicator. Soil samples from a non-agricultural area were incubated under controlled laboratory conditions for 28 days. Herbicides were applied at three dosages, while adjuvants were tested at label-recommended concentrations. Additionally, herbicide degradation was quantified using liquid chromatography. Results showed no significant differences in microbial respiration between treatments and untreated control, regardless of application rate. However, a modest increase in respiration was observed in soils treated with certain herbicides, notably Pluris® (19%) and Dominum® (23%), suggesting potential microbial stimulation. Adjuvants also exhibited no inhibitory effects, with Assist and VegetOil slightly enhancing respiration. Chromatographic analysis confirmed rapid degradation of all active ingredients, exceeding 80% within 28 days, with fluroxypyr degrading most extensively (97%). These findings indicate that, under the tested conditions, neither herbicides nor adjuvants adversely affect soil microbial respiration. Nevertheless, the observed variability highlights the need for field-based and long-term studies, particularly in integrated vegetation management scenarios, to better understand potential ecological implications and guide sustainable herbicide use in sensitive environments.