ARS | Publication request: 15N Isotopic Crop Exchange Residue Studies Suggest that IPCC N Input Methodologies to Assess N2O-N Emissions Should be Reevaluated

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 9, 2009
Publication Date: July 24, 2009
Citation: Delgado, J.A., Del Grosso, S.J., Ogle, S. 2009. 15N Isotopic Crop Exchange Residue Studies Suggest that IPCC N Input Methodologies to Assess N2O-N Emissions Should be Reevaluated. Nutrient Cycling in Agroecosystems. (doi:10.1007/s10705-009-9300-9).

Interpretive Summary: This paper summarized the results from large plot crop residue exchange studies. The 15N data clearly shows that the 31% N losses from the inorganic fertilizer inputs were significantly higher than the 13% N losses from the crop residue inputs. It is clear from these studies that the 26% of fertilizer N retained in the soil was much lower than the 73% of crop residue N retained in the soil. The data also show higher availability, mobility and transformation of the applied N fertilizer that quickly enters the available N pool for crop uptake. These 15N studies clearly show that on average the N release from crop residues will incur lower levels of N loss. The data presented in this papers suggest (pending additional data collection) that the IPCC crop residue N2O-N emissions coefficient of 1% should be lowered to account for the lower N losses from crop residues (soil and plant), especially the lower N losses with grains crop residues such as barley and wheat, which have higher C/N ratios and slower N mineralization rates.

Technical Abstract: It is difficult to quantify nitrogen (N) losses from agricultural systems to the environment, however we can use 15N isotopic techniques to conduct site specific studies to increase our knowledge about N management and fate. This manuscript synthesizes the review of two selected 15N isotopic studies conducted to monitor N fate. The mechanistic foci of these studies include crop residue exchange and the fate of N in farming systems. The review and synthesis of these studies support the claim that the average N losses from inorganic N fertilizer inputs are much greater than those from organic crop residue N inputs. Moreover, the data assembled in this manuscript support the conclusion that the current IPCC methodology should be changed by lowering the N2O-N emission coefficients in order to reflect less N2O-N emissions from crop residue N inputs, which has implications for public policy associated with the United Nations Framework Convention on Climate Change and mitigation of N2O emissions from agricultural soils. [GRACENet publication].