Pesticide leaching in polders : field and model studies on cracked clays and loamy sand

This thesis reports on a study of pesticide leaching in polder areas. The study comprises two aspects: a data collection program and the development, calibration and application of the model SWACRO for the simulation of pesticide transport. Field data were collected at three experimental fields, all situated in the IJsselmeerpolders. The experimental fields were situated on loamy sands and cracked clay soils. The model SWACRO was selected to describe water and solute flow in the (un)saturated zone. The model was extended to transport of pesticides and preferential flow. For the IJsselmeerplders the present legislation for the registration of pesticided should be adapted, taking into account that: (1) Leaching may contribute significantly to the presence of pesticides in surface waters (2) Leaching is highly influenced by preferntial flow.