ARS | Publication request: Bias in IPCC Methodologies for Assessment of N2O emissions from Crop Residue

Submitted to: Soil Science Society of America Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 7, 2009
Publication Date: July 11, 2009
Citation: Delgado, J.A., Del Grosso, S.J., Ogle, S. 2009. Bias in IPCC Methodologies for Assessment of N2O emissions from Crop Residue. Soil Science Society of America Annual Meeting.

Technical Abstract: Nitrogen use efficiencies are difficult to measure and reported recoveries from fertilizer N by crops average =50%. Worldwide studies (20+) conducted with precise 15N techniques that trace the fate of N found that an average of 66% of the fertilizer was recovered in crops and soils. In other words, 34% of the added N is lost from the cropping systems during the first year. There are no extensive 15N recovery data tracing the fate of organic N from crop residues after a year of crop residue incorporation. Four rotations using the Delgado et al. (2004) large 15N cover crop residue exchange design, which allowed for use of machinery equipment over the plots to simulate agricultural practices, resulted in an average recovery of 87% of the organic N from crop residues in soil and plants. The average losses from organic N added with crop residue were about 13%, much lower than the 32% N lost from inorganic N fertilizer in these four cropping systems, which suggests greater potential for N2O emissions from fertilizer N additions. We used these 15N findings to evaluate the accuracy of the methodologies currently used by the Intergovernmental Panel on Climate Change (IPCC). The current approach for measuring N2O-N emissions does not reflect the higher N losses from inorganic N fertilizer when compared to lower N losses from the much slower decomposition of the organic crop N residue pool. Default IPCC methodology uses the same N2O emission factor (1%) for N from crop residues as for N from applied fertilizer. These unique 15N crop residue exchange studies support the suggestion that the current IPCC methodology should be changed by lowering the N2O-N emission coefficients in order to reflect fewer N2O-N emissions from crop residue N inputs when compared to the N2O-N emissions from inorganic N fertilizer.