Significance of preferential flow as a transport mechanism for pesticides In lysimeters containing sandy soil cores

摘要

Outdoor lysimeter studies with undisturbed soil cores have become an important tool for the identification of pesticides with a leaching potential. Besides the vertical single phase pore flow, physical non-equilibrium effects such as 'preferential flow' might also be important transport mechanisms. Sorption and degradation kinetics determine the availability of the pesticide for leaching. Soil-intrinsic properties, however, also determine the pathways that water follows. In order to describe the significance of preferential flow paths, 23 outdoor lysimeters with undisturbed soil cores were taken from a field and applied with the water tracer 2,6-difluorobenzoic acid in autumn. Two different initial soil moistures were adjusted in the soil cores. Thevelocity of downward percolating water in each lysimeter was determined on the basis of the tracer concentration in the leachates. Tracer findings directly after application, unlike the main breakthrough of the tracer, were used to assess the relative importance of preferential flow effects in the individual lysimeter. It was possible to identify individual lysimeters (about 25%) with the potential for preferential flow. Lysimeter leaching studies should only be carried out with lysimeters if the history of the water and tracer transport is known.