Ecotoxicological Impact of Butisanstar and Clopyralid Herbicides on Soil Microbial Respiration and the Enzymatic Activities.

The application of herbicides in soil has been noted for its detrimental effect on the soil microbial community, crucial for various biochemical processes. This study provides a comprehensive assessment of the impact of butisanstar and clopyralid herbicides, both individually and in combination at different dosage (recommended field dose (RFD), ½, 2 and 5-times RFD). The assessment focuses on soil basal respiration (SBR), cumulative microbial respiration (CMR), and the activities dehydrogenase (DH), catalase (CAT), urease, acid and alkaline phosphatases (Ac-P and Alk-P) enzymes, along with their variations on days 10, 30, 60, and 90 post-herbicide application. Results indicate that, although herbicides, even at lower doses of RFD, demonstrate inhibitory effects on DH, CAT, and microbial respiration, they paradoxically lead to a significant enhancement in urease and phosphatase activities, even at higher doses. The inhibitory/enhancing intensity varies based on herbicide type, incubation period, and dosage. Co-application of herbicides manifests synergistic effects compared to individual applications. The most notable inhibitory effects on DH, CAT, and SBR are observed on the 30th day, coinciding with the highest activities of urease and phosphatases on the same day. The persistent inability to restore respiration and enzyme activities to initial soil (control) levels emphasizes the lasting adverse and inhibitory effects of herbicides, especially clopyralid, over the long term. It becomes apparent that soil microorganisms require an extended duration to decompose and acclimate to the presence of herbicides. Consequently, these agrochemical compounds pose a potential risk to crucial biochemical processes, such as nutrient cycling, ultimately impacting crop production.