Nitrogen Balances at Ecosystem, Landscape, Regional and Global Scales.

While the vast majority of soil nitrogen (N) cycling research is process-level, there is great interest in the dynamics of N at larger scales.  Indeed, the justification for much process-level work is frequently some relevance to ecosystem N balances, landscape movement of N from crop fields towards streams, regional N trace gas budgets or global N balances and climate change.  Translating information across scales is frequently identified as one of the greatest basic and applied science challenges facing agricultural and environmental science. In this poster, I review needs, progress and prospects for analysis of N balances at ecosystem, landscape, regional and global scales.  A common theme is addressing the challenge of scale, i.e. translating information from the process and field plot level, where most of our measurements are, to larger scales where information is needed to address specific questions.  N balances have been and will continue to be extremely useful tools for evaluating N cycling at multiple scales.  They are useful for evaluating the efficiency of fertilizer use, the environmental impacts of agricultural production systems and for integrating physical, biological and social science aspects of these systems.  Several points emerge from the review.  First, “missing N” is important in balances at all scales.  Inputs exceed outputs in the vast majority of studies, with significant amounts, e.g. 30% of input attributed to “storage” and “loss” processes that are poorly characterized.  Second, hydrologic and atmospheric measurements provide useful constraints on N balances.  In many cases, agronomic and atmospheric inputs are well measured.  In cases where hydrologic outputs are well measured, it is possible to quantitatively bound other processes, e.g. loss and storage, that are harder to measure.  Third, coupling N balances with economics and other social sciences at different scales is an important approach for solving agronomic problems related to N.