Single and dual-permeability models of chlorotoluron transport in the soil profile

This study presents the transport of chlorotoluron in the soil profile under field conditions. The herbicide Syncuran was applied on a plot (4 m²) using an application rate of 2.5 kg/ha of active ingredient. Soil samples were taken aer 119 days to study the residual chlorotoluron distribution in the soil profile. The single and dual-permeability models in HYDRUS-1D (Simůnek et al. 2003) were used to simulate water movement and herbicide transport in the soil pro- file. Soil hydraulic properties and their variability were previously studied by Kutilek et al. (1989). The solute trans - port parameters, such as the adsorption isotherm and the degradation rate, were determined in the laboratory. Since the solute transport in the field was probably affected by preferential flow, the chlorotoluron distribution in the soil profile calculated using the single-permeability model had a different character than observed chlorotoluron concen - trations. The chlorotoluron distribution within depth calculated using the dual-permeability model was closer to the observed behavior of chlorotoluron. While the herbicide did not reach a depth of 8 cm for the single-porosity system, in the case of the dual-permeability model the solute moved to the depth of 60 cm. The dual-permeability model sig- nificantly improved correspondence between calculated and observed herbicide concentrations.