Comparison of greenhouse gas offset quantification protocols for nitrogen management in dryland wheat cropping systems in the Pacific Northwest

Authors: BROWN, TABITHA - Washington State University; LEE, CARRIE - King County; KRUGER, CHAD - Washington State University; REGANOLD, JOHN - Washington State University; Huggins, David

Submitted to: Frontiers in Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the carbon market, greenhouse gas (GHG) offset protocols need to ensure that emission reductions are of high quality, quantifiable and real. However, lack of consistency across protocols for quantifying emission reductions compromise the credibility of offsets generated. Thus, protocol quantification methodologies need to be reviewed and improved to ensure emission offsets are credited accurately and support practical climate policy solutions. Under current GHG offset programs, emission offset credits generated by agricultural nitrogen (N) management activities are based on reducing the annual N fertilizer application rate for a given crop without reducing yield. We found that only two of the available four offset protocols were suitable for our study of dryland, wheat-based cropping systems of the inland Pacific Northwest. Here, reducing N fertilizer application rates by switching to variable rate N or using split N applications resulted in significant reductions in N2O emissions. It was also concluded that incentive payments for N2O emission reductions were unlikely to impact on-farm N management decisions. However, including the N fertilizer cost saving significantly increased the overall savings to farmers. The monetary incentive for agricultural N management for N2O emission reductions should be tied to existing conservation programs or other co-benefits to encourage N rate reductions that do not limit yield, crop quality, or economic stability. These results will be useful for those associated with carbon markets, producers, NRCS, Conservation Districts and scientists interested greenhouse gas assessment and offsets.

Technical Abstract: In the carbon market, greenhouse gas (GHG) offset protocols need to ensure that emission reductions are of high quality, quantifiable and real. However, lack of consistency across protocols for quantifying emission reductions compromise the credibility of offsets generated. Thus, protocol quantification methodologies need to be reviewed and improved to ensure emission offsets are credited accurately and support practical climate policy solutions. Under current GHG offset programs, emission offset credits generated by agricultural nitrogen (N) management activities are based on reducing the annual N fertilizer application rate for a given crop without reducing yield. We performed a “road test” of agricultural N management protocols to evaluate differences among protocol components and quantify nitrous oxide (N2O) emission reductions under sample projects relevant to N management in dryland, wheat-based cropping systems of the inland Pacific Northwest (iPNW). We evaluated four offset programs with agricultural N management protocols applicable to North America: the American Carbon Registry (ACR), Verified Carbon Standard (VCS), Climate Action Reserve (CAR), and Alberta Offset Credit System (Alberta). We found that only two protocols within these programs, ACR2 and VCS, were suitable for this study, in which four sample projects were developed representing feasible N fertilizer rate reduction activities. The ACR2 and VCS protocols had identical baseline and project emission quantification methodologies resulting in identical baseline, project, and emission reduction values. Reducing N fertilizer application rate by switching to variable rate N (sample projects 1-3) or split N application (sample project 4) management resulted in an estimated N2O emission reduction ranging from 0.07 to 0.16 and 0.26 Mg CO2e ha-1, respectively. Across the range of C prices considered ($5, $10, and $50 per metric ton of CO2 equivalent), it was concluded that the incentive payment for N2O emission reductions was unlikely to impact on-farm N management decisions ($0.35 to $13.0 ha-1). However, including the fertilizer cost saving increased the incentive payment considerably. The monetary incentive for agricultural N management for N2O emission reductions should be tied to existing conservation programs or other co-benefits to encourage N rate reductions that do not limit yield, crop quality, or economic stability.