Bentazon Degradation in Soil: Influence of Tillage and History of Bentazon Application

Laboratory studies determined the fate of bentazon (3-isopropyl-1 H -2,1,3-benzothiadiazin-4(3 H )-one 2,2-dioxide) in soil as affected by tillage and history of application. Bentazon degradation in two soils from Mississippi and three soils from Illinois under conventional-tillage (CT) and no-tillage (NT) (3−18 years) with varying histories of bentazon application (0−9 applications) was studied. The half-life (DT 50 ) for bentazon degradation ranged from 4.6 to 49.5 d; half-lives for NT of the two soils with the longest history of bentazon application were lower than those for CT. Half-lives for soils with no bentazon history were 3−11-fold higher than bentazon half-lives of those previously exposed to bentazon. Dissipation of bentazon was accompanied with increases in nonextractable material. Methylbentazon was the most consistently observed metabolite (1.7−5.8% applied 14 C after 48 d). Bentazon mineralization ranged from 12% to 18% applied after 48 d and 2% to 3% applied after 22 d for bentazon history and nonhistory soils, respectively. Patterns of mineralization were affected by tillage in the two of the five soils with the longest bentazon history.