Evaluation of the Impacts of Clopyralid and Butisanstar Herbicides on Selected Soil Microbial Indicators

Herbicide application is a widely utilized approach for weed management in agriculture. However, it is essential to acknowledge that these chemical compounds can affect non-target soil microorganisms and their functions. To address this concern, a pot experiment was conducted to assess the effects of Clopyralid, Butisanstar, and their combination (But + Clo) at different doses (zero, 0.5x, recommended field dose (x), 2x, and 5x) on microbial indicators, including microbial population, microbial biomass carbon (MBC), basal soil respiration (BSR), substrate-induced respiration (SIR), microbial quotient (q micro ), and respiratory quotient (qCO 2 ) at 10, 30, 60, and 90 days following their application to the soil. The results revealed a significant reduction ( p < 0.01) in all microbial indicators (except qCO 2 , which exhibited an increase) compared to the control soil after herbicide application. Among the treatments, the combination of But + Clo exhibited the greatest decrease, followed by clopyralid and butisanstar. Bacterial populations experienced a more pronounced and persistent inhibitory effect from the herbicides compared to fungi, with a significant decrease (67%) observed from day 10 to day 30, followed by a less substantial decrease (12%) until day 90. The impact of clopyralid and butisanstar on microbial indicators demonstrated a dose-dependent relationship, with the highest and lowest values observed at 0.5 × and 5x doses, respectively. Furthermore, the adverse effects of the herbicides resulted in a substantial reduction of the evaluated indicators, particularly during the initial 30 days following application. However, temporary recovery and an increase in microbial indicators (excluding bacterial populations) were observed on day 60, likely due to the microbial community's adaptation to the applied herbicides. This study emphasizes the negative consequences of herbicide application on the soil microbial community, raising concerns regarding soil health, quality, and fertility in relation to crop production.