Impact of precision application of herbicides on leaching to groundwater

Samenvatting

Currently the leaching to groundwater assessment as part of the pesticide registration procedure in the EU and the Netherlands does not consider precision applications. This report describes a study on leaching to groundwater of a herbicide which is applied using a variable application technique. Model simulations per applied patch in the field were compared to those based on a full field application. For this selected case results showed that the reduced (averaged) dose can be used in the leaching assessment for substances with linear sorption or weak non-linearity of sorption. For non-linear sorbing substances the differences between averaging of the dose and averaging of the leaching concentrations are probably larger. To generalize these results to the generic leaching assessment applied in the regulatory context additional steps are needed. In this report an outlook is given on how this could be done. The reduced dose should be derived probabilistically while using multiple example cases with variable rate applications in the area of use (the Netherlands) and soil information at a high spatial resolution. The main obstacle to derive such a generic approach is the current limited availability of established dose-soil scan parameter relations.