About the Workshop
The scale and scope of human alterations to the global cycles of nitrogen (N) and (to a lesser extent) phosphorus (P) have been the subject of a number of recent analyses and syntheses, and most global change scientists now are aware of the magnitude of these changes. The consequences of alterations to these biogeochemical cycles - eutrophication of lakes and coastal waters, increases in the greenhouse gas nitrous oxide, oxidant air pollution, interactions with the carbon cycle, losses of biological diversity - also are well-recognized in the global change community. Public recognition of the importance of these changes has lagged behind scientific understanding, and both scientific and policy engagement with managing the consequences of altered biogeochemical cycles has lagged as well in comparison with the focused international effort to mitigate anthropogenic changes to the carbon cycle.
We proposed that the Aspen Global Change Institute host a small working group focused on identifying and developing the information that society needs to respond effectively to anthropogenic changes in the cycles of N and P. We saw no need for yet another assessment of the N and P cycles. Rather, we believed that it was time to develop the information that would enable effective action to manage those changes. We identified two topics that we believed were fundamental to managing changes in N and P, and that may be ripe for progress; further, we believed that a dedicated group focused on these issues could identify other potential topics in which progress was feasible.
Both of the areas which we had identified were agriculturally-related, as expected since agriculture is the major cause of change in N and P. We should note that in keeping with the distributed nature of changes to the N and P cycles, there will be no single global challenge to be met. For example, it was clear that in much of Africa, agriculture doesn't have access to enough supplemental N in contrast to much of North America, Europe, and China, where the problem is one of too much N.
We suggested that one key topic in the N cycle was that there is a ceiling to the efficiency with which fertilizer N (synthetic or organic) makes it into crops. Regional and global analyses demonstrate that little more than 10% of the fertilizer N applied globally is actually consumed by humans. While there is substantial work designed to increase that efficiency, there are striking limits to the efficiency that intensive agriculture has been able to achieve. Even under the best circumstances, rarely does 50% of the massive amount of N applied to agriculture go into crops. There has been excellent work designed to increase the N efficiency of agriculture - but as long as there is an efficiency ceiling near 50%, then at best half of all N is going to places where it is wasted (from farmer's perspective) and potentially damaging to the environment. We do have ways to increase the efficiency of agricultural systems towards the ceiling - but are there paths towards increasing the efficiency ceiling itself? And if so, what are the environmental and policy implications?
For P, the challenge is different. P is relatively immobile in most soils, and much of the P applied to agricultural systems stays in soils - with only a fraction available to crops. Continued P fertilization thus enriches soils as well as crops, in contrast to N which is lost relatively quickly from ecosystems. As a consequence, it is often possible to detect ancient agricultural sites to which P has been added based on enriched P in their soils. Massive modern P applications enrich surface soils over a much wider area than did past systems, and associated modern agricultural practices enhance erosion. Consequently, P-fertilized agricultural soils represent a substantial and ultimately mobile source of P to downstream and downwind ecosystems, one that will continue to change recipient ecosystems for decades and centuries even if application were soon to cease (as it cannot). What can be done to reduce the accumulation of P in agricultural soils or the consequences of that enrichment? What can be done to lessen the impact of the massive stores of P that already exist in the environment?
These analyses (and others) must be carried out in the context of massive ongoing changes to agriculture, in both developed and developing countries. For example, meat and dairy demand continues to grow in the middle income countries, encouraging the development of industrial livestock systems. Moreover, to the extent biofuels increase as a component of developed world agriculture (as they likely will, both where they make sense and where they do not), alterations to N and P will expand, intensify, and potentially take new forms that we ought to try to anticipate. Dead zones in the Gulf of Mexico and elsewhere are one serious result from the intensification of agriculture. A recent global assessment noted 400 coastal zones, affected, covered an area of more than 245,000 square kilometers. An interdisciplinary systems approach is required to develop sustainable pathways for N and P management considering both mitigation and adaptation issues.
Useful analyses of managing the consequences of human alteration of N and P will require contributions from a number of fields - including biogeochemistry, agriculture, policy, soils, ecosystems, and others. We suggested that a small three-day meeting would be both efficient and rewarding. AGCI invited participants from two countries with expertise in areas around the world. The meeting was designed to yield a policy paper suggesting research strategies and applications that were published in PNAS or Frontiers in Ecology and Environment, as well as a publication in Annual Review of Environment and Resources. It also contributed to the development of the International Nitrogen Initiative, newly under the leadership of Cheryl Palm.
An article summarizing the findings of the workshop has been submitted to Science.
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