BENTAZONE LEACHING IN SPANISH SOILS

Adsorption, incubation and soil-column experiments with bentazone [3-i sopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were carried out in ten different soils from the marches surrounding the Donana Nat ional Park (Huelva, SW Spain). Adsorption isotherms for the different soils showed a good fit with the Freundlich equation. Bentazone was po orly adsorbed in all the soils studied, with no significant relationsh ip between the K-f values and soil characteristics. A significant corr elation was obtained between the soil organic matter content and the d istribution constant values (K-d) calculated at an equilibrium concent ration of 200 mu g cm(-3). The low adsorption and non-degradation of b entazone on these soils suggest that the herbicide readily percolates through soils to reach the surface and ground waters. The mobility of bentazone through three soil columns was also studied. The mass balanc es carried out showed that bentazone was totally eluted from the soil columns. The theoretical model applied to explain bentazone leaching u nder our experimental conditions seems to be suitable for soil columns with a uniform water-flow rate.