Work

Residual effect vs. degradation of S-metolachlor in tropical soils: Herbicide analysis by sorghum bioassay and HPLC

Year: 2026

Type: article

Abstract: The use of pre-emergence herbicides, such as S-metolachlor, has stood out in the management of hard-to-control weed species. Its behavior in the soil, influenced by environmental and physicochemical factors, determines both the efficacy and the safety of weed management. In this context, the aim of this study was to determine the residual effect by bioassay and the degradation of S-metolachlor by high-performance liquid chromatography (HPLC) in two soils (Oxisol and Ultisol). Soil samples were collected from Pato Branco/PR (Oxisol) and Paranavaí/PR (Ultisol), without prior herbicide application. A completely randomized design with a 2 × 10 factorial scheme (two soils and ten application times: 0, 7, 14, 21, 28, 35, 70, 90, and 120 days) was used. The residual effect was analyzed via a Sorghum bicolor bioassay, while degradation was assessed through HPLC. The main parameters included residual half-life (RL 50 , RL 90 ), dry matter reduction (GR 50 , GR 90 ), and degradation time (DT 50 , DT 90 ). In Oxisol, which had higher organic matter and clay content, values were lower (RL50 = 32 days, RL 90 = 107 days, GR 50 = 28 days, GR 90 = 29 days, DT 50 = 32 days, DT 90 = 106 days) than in Ultisol (DT 50 = 53 days, RL 50 , RL 90 , GR 50 , GR 90 , and DT 90 > 120 days). The physicochemical properties of these soils influenced S-metolachlor behavior, primarily due to differences in bioavailability within the soil solution, as reflected in bioindicator species response. While residual effect denotes the duration of herbicide activity, degradation refers to molecular breakdown over time. Both factors are essential for weed management strategies.

Source: Journal of Hazardous Materials Organics

DOI: 10.1016/j.hazmo.2026.100017