A methodology to support the decision to invest in spatially variable nitrogen fertilisation

This paper reports a methodology to define and select basic activities for spatially variable N-management, referred to as management tracks. Their ma in purpose is to support decision making whether or not to apply variable n itrogen fertilisation. The methodology is based on biophysical simulation o f crop growth and nitrogen leaching (WAVE) in combination with economic opt imisation (linear programming) and enables a normative environmental-econom ic evaluation of site specific N-management to be made. The partial results of a case study with an input-intensive and an input-extensive crop (ware potato and winter wheat, respectively) showed that site specific nitrogen m anagement led to positive returns over variable costs compared to uniform N -application, conditional on the validity of the WAVE model used in simulat ing yield effects. The investments that could be allowed for at maximum wer e 6,300 Dfl and 13,500 Dfl for winter wheat and ware potato, respectively, assuming application to an area of 100 ha. A pollution tax or a tax on nitr ogen designed to internalise pollution costs in agricultural production rai ses these maximum amounts to 7,600 and 33,700 Dfl, respectively. practical feasibility requires site-specific nitrogen management to be integrated wit h time specific management since optimal N-tracks were found to be highly w eather dependent. Besides, spatially variable management cannot be achieved unless good farming practices (soil testing and crop scouting) are already in place.