Application of pesticide simulation models to the Vredepeel dataset: I. Water, solute and heat transport

The performance of 10 deterministic one-dimensional dynamic pesticide leaching models with different complexity was evaluated using data collected on a humic sandy soil with a shallow ground water table in the Netherlands. Both mechanistic models, based on the solution of the governing How equations (the Richards equation for soil water and the convection dispersion equation for solute flow) and functional, more empirical models were considered in the analysis. Simulations were carried out by 18 modellers allowing the characterisation of model performance in terms of user specific model parameterisation. Both uncalibrated and calibrated results are presented which demonstrate the impact of model calibrations on modelling results. In this paper, the ability of the models to correctly represent the physical transport processes is evaluated, while in a subsequent paper (Tiktak, 2000. Agric. Water Manage. Vol. 44, pp 119-134), the potential of the models to represent pesticide fate correctly will be assessed. Model calibration had a major impact on the simulation of water flow in soils. In general, after calibration, the Richards' type models were superior to the capacity type models. However, user-specific hydraulic parameter estimation procedures introduce considerable variability in model performance which sometimes overrules conceptual model differences (Richards'/capacity). The evaluation of the solute transport component of the models was inhibited by the lack of reliable tracer data. Heat transport modelling in the top soil was not felt as being a bottleneck in our modelling technology. A plea is made for developing good modelling practices in which guidelines for selecting robust parameter estimation methods are defined. (C) 2000 Elsevier Science B.V. All rights reserved.