The nitrogen cycle, scientific uncertainty and policy relevant science.

Much of the research on the nitrogen cycle aims to improving scientific understanding but is not focused specifically on removing or reducing the scientific uncertainties that constrain policy makers in the formulation of appropriate responses to old or emerging environmental problems. Policy makers, for example, commonly find it difficult to assess the spatial or temporal importance of the various risks to human and ecosystem health that stem from man's interference with the natural N cycle. This paper will justify this conclusion by reference to the findings of a recent study on non-point pollution from crop production in China. The findings concern the perceived risks of groundwater nitrate to human health; uncertainties about critical NO(x) levels and their interactions with other pollutants; various other dimensions of man's impact on the N cycle. The paper will go on to suggest a more systematic process or pathway by which scientists can select and design their research in a manner that could give more effective support to policy makers.