ABSTRACT
The central theme of the chapter is the development of the non-point source NITrogen and PHOsphorus SOiL model (NITSOL/PHOSOL). The models describe the behaviour of N and P in soils. Currently the models operate within an extended computational framework for integral water management and have proved to be a solid instrument of support in decision making. We used the models during the past 12 years for studies on a local, regional and national scale. From these experiences we subtracted our ideal set of data for calibration and verification. The practical potential of the models is illustrated using examples from two catchment areas, Horst and Hupsel.
We conclude that the models are especially useful to test the effects of legislation and to select the Best Management Practices (BMP). In this context, we would advise the use of models as a sensitivity instrument, especially with respect to critical input data. More generally, we conclude that legislation in the Netherlands should specify, apart from P quantities, the maximum admissible supply in terms of N-quantities. We finally strongly recommend the use of models in an early stage of environmental research, stretching the mind of the manager.
