Soil moisture affects leaching behaviour of pesticides. For the example of Betazon, Guimont et al. (2005) could show for water percolated columns with soil aggregates, that soil moisture induces the physical entrapment in the soil structure.
Giuliano et al. (2016) monitored for different maize cropping systems water drainage and pesticide leaching, using tension plate lysimeters, installed at 1 m depth. Two indicators were used to compare the drainage and pesticide leaching of the cropping systems: the cumulative drainage per year (expressed in mm) and the number of pesticide leaching events with at least one compound (mother compound or metabolite) quantified at a concentration≥ 0.1 µg/l (corresponding to the limit for drinking water).
Herbicides may leach under the influence of artificial irrigation or rainfall events, an effect that was more pronounced in medium soils with low organic matter content (Monquero et al., 2008). Fait et al. (2010) studied the effect of the three different irrigation methods sprinkler, basin or border systems on the leaching of the herbicide Terbuthylazine (TBA) and its metabolite Desethylterbuthylazine (DEB) in ground water on ten farms in Italy cropped with maize. The results showed that basin irrigation led to the highest concentrations in the ground water, indicating that this irrigation system can influence the leaching of both TBA and DEB. Irrigation can also lead to pesticide leaching by preferential flow, especially during the first days after application (Schierholz et al., 2000). From these studies, it can be concluded that pesticide transfers are increasing when the water content is increasing.