There is ample experimental evidence that complications in water flow and pesticide transport can occur in cultivated humic-sandy and loamy-sandy soils. As a result, pesticide leaching to groundwater and water courses can be higher than expected. We made an inventory of mechanistic/deterministic model concepts that may be suitable for simulating preferential water flow and pesticide transport in these soils. The convection-dispersion approach, the mobile-stagnant concept, the dual-velocity concept, the explicit description of horizontal diffusion, the soil column approach and a concept of finger flow are discussed. Only for comparatively simple concepts it is feasible to ever obtain the parameter values. Ideally, the data sets to be used for testing the models concepts should be detailed and complete. Discrimination between the validity of the model concepts requires the variation in the measuring results to be limited. Testing of the model concepts under various representative field conditions is needed, to gain confidence in their results.
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