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Many soil properties that are used as parameters in solute transport models vary in space. Their use as parameters is assumed to be valid provided the assembly of values remains constant with time. Nonlinearity in models interacts with this variance giving possibly misleading results when a model is used, and care is needed with both simple and spatial averaging procedures. Averaging or interpolating the parameter before running a nonlinear model does not give the same result as running the model and then averaging or interpolating the results. This difference could be important for some uses to which solute transport models are put, particularly for large areas. A simple test for nonlinearity is suggested for use as part of sensitivity analysis. It is important to know how the variance changes as the area over which a model is used increases. This makes the variogram of the property used as a parameter a relevant part of sensitivity analysis. Land use may affect both the properties of the soil that determine solute transport and the generation of nitrate within the soil; however, sensitivity analysis of models describing land use effects may be difficult, because it is hard to see how a system for analyzing such sensitivity would differ from a system used in practice to provide decision support. The results of the study support the conclusion that capacity-type models will be the most useful for simulation of solute transport in large areas.