Soil erosion may play an important role in particular N and P surface transport to surface waters. Soil erosion can also constitute a major pathway for surface transport of pesticides via soil colloids, especially in subtropical and tropical countries with high intensity precipitation events. It is usually not part of indicators in Europe, where mostly only drift or runoff are considered as pesticide discharge pathways (Holmes, 2014). In a long term soil erosion experiment in Austria, the soil type as well as the cropping system influenced the amount of surface runoff, including pesticide losses, from fields cultivated with maize and winter wheat significantly. While in silty loam textured soils mulch till and no-till led to 14-56 % less surface runoff compared to conventional tilled soils, on fields with loamy soil the low till methods led to an 12-20 % increased surface runoff. This was explained by an increased soil compaction due to the omitted ploughing, leading to a decreased water infiltration into the soil (Klik and Strohmeier, 2011). Also, Vogel et al. (2016) report a 90-100 % reduction of soil erosion due to no till farming and conservation tillage compared to conventional tillage, while other measurements such as buffer strips or permanent grassed waterways had minor effects in reducing surface runoff, especially following severe precipitation events. Open questions remain regarding the influence of no-till systems on preferential flow paths.
However, in a study by Ulrich et al. (2018) in ten small water bodies, it was noted that site characteristics such as soil type, humic content and slope did not explain the differences in accumulation of two herbicides and their transformation products in the water bodies. Rather, the precipitation after pesticide application, interaction with the shallow groundwater or subsurface transport of the products were responsible for higher pesticide transport into the ponds.
Based on their runoff potential, soils are classified by the United States Natural Resources Conservation Service (NRCS) into four hydrological soil groups A to D. Hydrologic soil groups were derived from the texture classes in top and sub soil (Panagos et al, 2012b) and the depth of the gley horizon (Stolbevoy et al., 2007).
For the program SYNOPS-WEB, Stassemeyer et al. (2017) used exposure models for drift, runoff and erosion based on spatially explicid data sets as European Soil Database, temperature and precipitation data (Hijmans et al., 2005) and crop growth scenarios FOCUS (2000).