LABORATORY METHOD FOR STUDYING PESTICIDE DISSIPATION IN THE VADOSE ZONE

A laboratory apparatus was constructed to study the leaching behavior of soil-applied herbicides in disturbed and undisturbed soil column under vadose zone conditions. The setup was built in such a manner that a broad variety of field conditions regarding rainfall characteristics and soil water tension could be simulated. Long-term transport experiments up to 3 mo required an automatic withdrawal of the soil percolate and a continuous control and recording of the soil water tension, the applied vacuum, and the amount of precipitation. During the sampling of the leachate, a newly designed lock guaranteed a constant vacuum at the bottom end of the soil column. First experiments with the new apparatus showed an earlier breakthrough of terbuthylazine (2-chloro-4-ethylamino-6-terbuthylaminotriazine) and a larger solute dispersion under transient water flow than under steady-state water now in a sandy soil.