The Nutrient Flow Model for Dutch Agriculture: A Tool for Environmental Policy Evaluation

The Nutrient Flow Model (NFM) is a micro-simulation model. It describes economic activities and corresponding nutrient flows at farm level for present and future situations in which environmental policy measures are taken. The farm results are aggregated to regional and national levels. The model can be used as an insrument for monitoring and policy evaluation. Technical aspects are incorporated into the model by means of crop growth models and nutrient balances for animals. Economic aspects are partly incorporated and partly added exogenously. The information need for the NFM is rather extensive. Main data sources are the Dutch Agricultural Census and the Dutch Farm Account Data Network. The model tries to combine the detailed approach with respect to production activities and nutrient flows that is often found in models at farm level with the more global approach that is followed in economic models on sector level. The variation in emissions between farms is dealt with explicitly. This paper presents the general concept of the NFM. It shows that the validation of technical models used in the NFM, on the basis of empirical data, is essential from the point of view of nutrient losses. An example is given of the assessment of the effects of government policies: the obligatory injection of manure may lead to a decrease in ammonia volatilisation but, at the same time, to an increase in nitrate leaching. The integrated approach of dealing with different nutrients simultaneously, taking into account all inputs and outputs, describing the complete chain of nutrient flows within farms, and modelling the interaction between farms makes the NFM a suitable instrument for the evaluation of environmental policy.