Assessment of the parameters of a mechanistic soil-crop-nitrogen simulation model using historic data of experimental field sites in Belgium

Intensification of the agricultural sector and the increase in quantity and decrease in quality of municipal and industrial wastewater, in particular during the past decades, resulted in many industrial countries, such as Bel gium, in a sharp degradation of surface water and groundwater. To control t he current degree of contamination and reduce the environmental impact of t he agricultural sector, the Flemish government recently introduced a number of regulations aiming at controlling the use of nitrogen fertilisers. To f acilitate the implementation and the control of the new regulations, thresh old values of allowable doses of organic and inorganic nitrogen fertilisers , and their spreading in time were made soil independent. As the soil physi cal, chemical and biological response depends on the geohydrology of the si te and the past fertilisation practice, fertiliser standards applied on dif ferent soil-crop systems result in different leaching patterns. To assess the effect of the soil on the nitrogen leaching, a number of past experimental field trials were analysed using the WAVE model as modelling tool for the reconstruction of the nitrogen dynamics. As a first step in th e study, the historic data of the field experiments were used to calibrate and validate the WAVE model. The deterministic calibration and validation o f the WAVE model yielded a set of model parameters for the examined soil-cr op-fertiliser practice conditions. The bottlenecks in the calibration were the nitrogen mineralisation parameters and the initialisation and subdivisi on of the soil organic matter over the different organic pools. The model v alidation, being the second step in the study, revealed the power of the WA VE model to predict the evolution and transformations of nitrogen in the so il profile and the leaching of nitrate at the bottom of the root zone. In a third step, the WAVE model was used in a scenario-analysis exercise to exa mine the factors effecting the amount of nitrate leached at the bottom of t he root zone. This analysis revealed that the nitrate leached out of the so il profile is controlled by the fertiliser practice, the rainfall depth and its distribution. the soil texture, the soil mineralisation capacity and t he past fertilisation practice. (C) 2001 Elsevier Science B.V. All rights r eserved.