From exec. summary: ...The purpose of the study was to develop a methodology that could be used to calculate emission reduction offsets from activities associated with nitrogen-based fertilizers in US agriculture. To have credibility in the developing carbon market the methodology would have to accurately represent the impact on the atmosphere and would involve the input of significant site-specific data. Thus the Intergovernmental Panel on Climate Change (IPCC)'s Tier 1 approach is far from sufficient as it simply multiplies the quantity applied by defaults to calculate emissions. Yet a methodology must not be excessively expensive to implement as it would preclude the possibility of any project being implemented thus direct measurement of nitrous oxide from fields using measurement chambers could not be considered. A methodology was chosen for testing that included site specific information on type of fertilizer, soil carbon concentration, drainage, pH, soil texture and crop type. The highly parameterized, tested and peer-reviewed model DNDC (Denitrification-Decomposition) was used to estimate the "real" atmospheric impact at the test sites. Test sites were chosen in Arkansas (cotton), Iowa (corn) and California (lettuce) for the 2009 growing season.... Neither the IPCC Tier 1 method nor the new method proposed here based on Bouwman et al (2002) are sufficient for an offset project methodology that would be able to evaluate atmospheric impact of a broad range on fertilizer management practices. Therefore alternative approaches must be considered.... This comparison highlighted a further weakness of the simplified models; the simplified models can only evaluate the impacts of changes in quantify of fertilizer applied not in the methods of application....The recommendation arising from this report is to develop an offset methodology based on the application of DNDC for projects. A DNDC methodology will require expertise but atmospheric integrity is better guaranteed, monitoring would likely be inexpensive and costs would be low considering that offset projects are likely to consist of aggregations of large numbers of farms.
