Agricultural Soil N 2 O Emissions in the US Greenhouse Gas Inventory: A Comparison of Methodologies...
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Transcript of Agricultural Soil N 2 O Emissions in the US Greenhouse Gas Inventory: A Comparison of Methodologies...
Agricultural Soil N2O Emissions in the US Greenhouse Gas Inventory:
A Comparison of Methodologies
Margaret Walsh1, Steve Del Grosso2, and Tom Wirth3
1 ICF Consulting2 USDA Agricultural Research Service3 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.
Waste (2.7% )
Industrial Processes (4.5% )
LUCF (0.1% )
Solvents (0.1% )Agriculture
(6.3% )
Energy (86.4% )
2003 Agriculture Sector Emissions
Agricultural Soil
Management (N2O) 58.5%
Enteric Fermentation (CH4) 26.5%
Manure Management (N2O and CH4)
13.1%
Rice Cultivation (CH4) 1.6%
Agricultural Residue
Burning (N2O
and CH4) 0.3%
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
Manure N
Synthetic N
Mineral Soils Organic
Soils
Atmospheric N2O
Direct Emissions
Indirect Emissions
Temperate:8 Tg N2O/haSubtopics:
12 Tg N2O/ha
1.25%
NH3 & NOx Volatilization (10% Synthetic N, 20% Manure N)
NO3- Leaching/Runoff (30%)
1%
2.5%
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
0
50
100
150
200
250
300
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
N2O
Em
iss
ion
s(T
g C
O2
Eq
)
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
0
50
100
150
200
250
300
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
N2O
Em
issi
on
s(T
g C
O2
Eq
)
IPCC
DAYCENT
Average Difference = 11.7%
0.6%
0.7%
0.8%
0.9%
1.0%
1.1%
1.2%
1.3%
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
Imp
lied
EF
(g N
2O/g
Fe
rtili
ze
r N
)Emission Factors
IPCC EF: 1.25%
DAYCENT EF wrt Total Added N Average EF = 0.95%
10%
15%
20%
25%
30%
35%
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
Lea
chin
g &
Ru
no
ff P
rop
ort
ion
(g N
lea
ch
ed
/g a
dd
ed
N)
Nitrate Leaching & Runoff
IPCC L&R Factor: 30%
DAYCENT L&R Factor wrt Total N Avg = 20.9%
0%
5%
10%
15%
20%
25%
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
Vo
latil
izat
ion
(g N
Ox-
& N
H3-
N/g
ad
de
d N
)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%)
What do these Differences Mean?
Variable DAYCENT vs. IPCC
Net Effect
N Inputs
Leaching & Runoff
Volatilization
Emission Factor
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: [email protected]