The world’s nitrogen cycle and human impacts

Abstract Text:

Perhaps 40 percent of the people alive today are sustained from increased grain yields attributed to the use of synthetic nitrogen fertilizer.  While the Haber-Bosch process of converting atmospheric nitrogen to ammonia (i.e., fertilizer) has transformed agricultural production, it has also caused an unprecedented shift in the global nitrogen balance.  Despite many improvements in nitrogen use efficiency in both crop and livestock systems, a large fraction of agricultural nitrogen inputs are lost to the environment.  This “fugitive” nitrogen is causing a host of environmental problems at local and global scales.  Excess nitrogen has been shown to alter biogeochemical processes and ecosystem function across the globe.   Because nitrogen can be easily transported in water or air through natural processes, or by the transport of grain and livestock; the impacts of agriculture nitrogen are often observed far from where the nitrogen was initially used.  A good example of this process is the observed increases in the atmospheric deposition of reactive nitrogen across many areas, including many pristine ecosystems.  Nitrogen deposition is often linked to ammonia-derived aerosols, compounds that can travel hundreds of kilometers from the source before being redeposited back to the surface. Because livestock account for over 50% of all ammonia emissions in many regions; beef feedlots, dairies, and swine and poultry operations are often linked to this air quality issue. While there is no question that livestock ammonia emissions are large, quantifying the actual impact of reactive nitrogen on the environment is a complex question.  One must consider atmospheric transport at both local and regional scales, chemical reactions with pollutants from other industries, and other non-livestock sources and forms of nitrogen. Perhaps nowhere has this issue been more investigated than along the Front Range of Colorado, where a mature cattle feeding industry is located relatively close to  the pristine ecosystems in Rocky Mountain National park. This presentation will begin with the role of livestock in the global and U.S. nitrogen cycle, and then narrow the scope to specific issues facing livestock producers in Colorado regarding atmospheric ammonia.  Summary comments will suggest how animal scientists and industry leaders might respond to these growing concerns. 

Keywords: Colorado producers, atmospheric ammonia, nitrogen