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Agricultural Soil N 2 O Emissions in the US Greenhouse Gas Inventory: A Comparison of Methodologies. Margaret Walsh 1 , Steve Del Grosso 2 , and Tom Wirth 3 1 ICF Consulting 2 USDA Agricultural Research Service 3 Non-CO 2 Gases and Sequestration Branch, US EPA (Formerly). Overview.
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Agricultural Soil N2O Emissions in the US Greenhouse Gas Inventory:A Comparison of Methodologies Margaret Walsh1, Steve Del Grosso2, and Tom Wirth3 1 ICF Consulting 2 USDA Agricultural Research Service 3 Non-CO2 Gases and Sequestration Branch, US EPA (Formerly)
Overview • The US GHG Inventory • Ag N2O • Evolution of Methodologies • IPCC’s Default Method • DAYCENT Simulation • Differences • Inputs • Emission & Partitioning Factors • Conclusions
Inventory of U.S. Greenhouse Gas Emissions and Sinks • Identifies and quantifies the US’s primary anthropogenic GHG sources and sinks • Commitment under the UN Framework Convention on Climate Change • Published annually • Undergoes extensive review process (internal, multi-agency, expert, public, international, UN) • 2005 Review Draft Available Online at: http://yosemite.epa.gov/oar/globalwarming.nsf/content/ResourceCenterPublicationsGHGEmissionsUSEmissionsInventory2005.html • Final available at the same URL on 15 April
2003 US GHG Inventory Sources Total Gross Emissions: 6,900.2 Tg CO2 Eq. Note: Total does not sum to 100% due to independent rounding.
2003 Agriculture Sector Emissions Total Emissions: 433.3 Tg CO2 Eq. Note: Total does not sum to 100% due to independent rounding.
In 2005, we’ve moved from a Tier 1 to a Tier 3 Methodology Tier 1: IPCC Default Methods using Nationally Available Data Tier 3: Simulation Modeling, using a Spatially & Temporally Explicit Representations of Biogeochemical Processes
IPCC Method Direct Emissions Indirect Emissions Synthetic N NH3 & NOx Volatilization (10% Synthetic N, 20% Manure N) Manure N NO3- Leaching/Runoff (30%) Mineral Soils Organic Soils 2.5% 1% Temperate: 8 Tg N2O/ha Subtopics: 12 Tg N2O/ha 1.25% Atmospheric N2O
Tier 3 Simulation: DAYCENT • Process • County-Level N Inputs, Soil Info, Climate Data • Daily Timestep • Results • Calculates Volatilization and Leaching Based on Immediate Conditions • Does not Distinguish Organic vs. Mineral Soils • Does not Distinguish N Sources
How do the differences in calculation methodologies lead to different results?
U.S. Cropland Soil N2O Emissions IPCC DAYCENT Average Difference = 14.2%
N Inputs • IPCC: 1.25% EF is applied to all consumed N fertilizer and reported within the Ag Sector, regardless of application. • DAYCENT: Fertilizer application rates are considered by crop and geographic region. 90% of consumed fertilizer is accounted for in this way. • The residual is applied (primarily) to settlement soils, and (secondarily) to forest soils. • Isolated, the net effect would be to reduce emissions.
U.S. Managed Soil N2O Emissions IPCC DAYCENT Average Difference = 11.7%
Emission Factors IPCC EF: 1.25% DAYCENT EF wrt Total Added N Average EF = 0.95%
Nitrate Leaching & Runoff IPCC L&R Factor: 30% DAYCENT L&R Factor wrt Total N Avg = 20.9%
NOx & NH3 Volatilization IPCC Volatilization Factor for Manure N (20%) IPCC Volatilization Factor for Synthetic N (10%) DAYCENT Vol Factor for Synth N(Avg = 2.6%) DAYCENT Vol Factor for Manure N(Avg = 2.0%)
In Conclusion • Nationally, Ag Soil N2O is a Key Category. • IPCC Guidelines are being revised now. Revised drivers (indirect fractionation & EFs) should be considered. • For more info: mwalsh@icfconsulting.com