agricultural strategies for mitigating ghg emission: agricultural strategies for mitigating ghg...
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Agricultural Strategies for Mitigating GHG Emission:
DNDC Model and Case Studies
February 18, 2010
Dr. William SalasApplied Geosolutions, LLC
87 Packers Falls RoadDurham, NH 03924 USA
APPLIED GEOSOLUTIONS, LLC
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OverviewSources and estimation methodologies of agricultural of greenhouse gases (GHG)Overview the DNDC models, How well does the model work? Discussion of model validation, California rice case study: Using the model for GHG inventory and assessing mitigating opportunities.
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Agricultural CH4 and N2O Emissions
Ag ~35% of total CH4 emission
Ag ~73% of total N2O emission
Source: USEPA GHG Inventory
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How do we estimate GHG emissions from agriculture?
MeasurementsMicrometerologicalmethods: area sourcesFlux chambers: site specific
Emission FactorsUse activity data * EF (e.g. N2O emissions = 1% of Nitrogen applied to crops)
ModelsSimple empirical modelsMechanistic (also known as process models)
E = A x EF x (1-ER/100)where:E = emissions; A = activity rate; EF = emission factor, and ER =overall emission reduction efficiency, %
DAYCENT Model
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What are Process-based Models?
Process-based modeling refers to biochemical and geochemical reactions or processesBiogeochemical processes… like decomposition, hydrolysis, nitrification, denitrification, etc…True process-based models do not rely on constant emission factors. They simulate and track the impact on emissions of varying conditions within soil and crop environment
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Why do we need Process Models?
Figure Source: Luo and Guo, ARB
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Role of Soil Carbon in CH4 and N2O Mitigation in Agricultural Soils
100000
102000
104000
106000
108000
110000
112000
114000
116000
118000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Year
SOC
, kg
C/h
a
Intensive tillageNotill
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Year
N2O
flux
, kg
N/h
a/yr
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Unexpected Consequences?
C sequestration
N2O flux SOC-GWP N2O-GWP Net GWP
kg C/ha/yr kg N/ha/yr kg CO2 equivalent/ha/yr Intensive tillage
125 11.5 -459 5615 5156
Notill
468 21.1 -1716 10301 8585
C sequestration
kg C/ha/yr Intensive tillage
125
Notill
468
C sequestration
N2O flux
kg C/ha/yr kg N/ha/yr Intensive tillage
125 11.5
Notill
468 21.1
Static emission factors do not capture spatial or temporal variabilityin emissions across range of management alternatives…
Need tools for comprehensive assessment (C sequestration, CH4 and N2O) of potential mitigation projects.
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Advantage of Process-based Models
Capture impact of soils on C and N cycling and GHG emissionsCapture variability of weather/climate on C and N cyclingCan be used to simultaneously assess impact of management practices on crop yields and GHG emissionsCan be used to assess a wide range of ecosystems services (climate, food/fiber, air quality, water quality)
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DNDC Model
DNDC stands for Denitrification and Decomposition, two processes dominating losses of N and C from
soil into the atmosphere, respectively.
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DNDC Biogeochemical Model Suite:
DNDC First model, development started in 1990Initial focus on N2OFocus on crop lands (>20 types of crops) Models CO2, CH4, N2O, and crop growth/yields
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DNDC Biogeochemical Model Suite:
Forest and Wetland DNDC
Added forest growth/physiology model to DNDCSimulates both wetland and upland forestsCan simulate seasonally flooded systems
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DNDC Biogeochemical Model Suite:
Manure-DNDCSimulates full C and N cycling for animal feeding operations.Models GHG and NH3 emissions from Animal, manure storage and management, and land application of manure.
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The Earth‘s Biomass: Soil Microbes (31100 Tg C) vs. Human (98 Tg C)
Quantifying GHG Emissions from Soils: Scientific Basis and Modeling Approach
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Scientific Basis
Soil Trace Gas Evolution Driven by Redox Potential (Eh)
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DOC
Electron acceptor
O2
NO3
Org-C
CO2 N2O CH4
Release electrons
Greenhouse gases are byproducts of microbial survival
Eh-determined drivers
- Decomposers
- Denitrifiers
- Methanogens
Gain energy
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DOC
Electron acceptor
O2
NO3
Org-C
CO2 N2O CH4
Eh
Farming practices affect GHG emissions through…
Tillage
Fertilization
Manure use
Irrigation
Crop rotation
Soil reclamation
Micro-meteorology
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The DNDC Modelecologicaldrivers
Climate Soil Vegetation Human activity
soil environmentalfactors
Temperature Moisture pH Substrates: NH4+, NO3
-, DOCEh
Denitrification Nitrification Fermentation
Decomposition
Plant growth
Soil climate
NH4+
clay-NH4
+NH3
DOC nitrifiers
NO3-
N2O NO NH3
DOC
NO3-
NO
N2O
N2
NO2-
nitrate denitrifier
nitrite denitrifier
N2O denitrifier
CH4CH4 production
CH4 oxidation
CH4 transport
soil Eh
aerenchyma
DOC
soil tempprofile
soil moistprofile
soil Ehprofile
O2diffusion
O2 use
verticalwaterflow
very labile labile resistant
litter
labile resistant
labile resistant
microbes
humads
passive humus
CO2
DOC
NH4+
roots
stems
grain
N-demand
N-uptake
water demand
water uptake
water stress
daily growth
root respiration
potentialevapotrans.
LAI-regulatedalbedo evap. trans.
effect of temperature and moisture on decomposition
annual averagetemp.
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DNDC bridges between ecological drivers and GHG emissions
INPUTINPUTINPUT PROCESSES OUTPUT
Climate- Temperature- Precipitation - N deposition
Soil properties- Texture- Organic matter- Bulk density- pH
Management- Crop rotation- Tillage- Fertilization- Manure use- Irrigation- Grazing
DNDC
1. Soil water movement2. Plant-soil C dynamics3. N transformation
Availability of water, NH4, NO3, and DOC
Used by soil microbes
Used byplants
Emissions of N2O, NO, N2, CH4 and CO2
Growth of cropbiomass
Competition N leaching
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Model Validation…Rigorous model validation is key for acceptance (scientific and market)Lack of appropriate field data for process-model validationDNDC has been validated extensively for agroecosystems worldwide (over 100 peer review papers)Additional validation efforts underway for California cropping systems
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Field Measurements of N2O and CH4
Measurement approaches:Flux chambers: site specific – useful for model validation if all model inputs are knownMicrometerologicalmethods: area sources – useful for evaluating regional model simulations (scaling from site to region)
Accuracy/uncertainty of measurements?
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Field Measurements & UncertaintyUncertainty of field measurements due to methods is quite variable.
05
1015202530354045
Per
cent
of F
lux
Mea
sure
men
ts
High (<10%) Medium (<30%) Low (10-50%) Very Low (20-60%)
Level of Confidence
1995-1999 2000-2004 2005-2207
Source: Rochette and Eriksen-Hamel, SSSAJ:72(2) March-April 2008
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Nitrous Oxide ValidationObserved and DNDC-Modeled N2O Fluxes from Agricultural Soils in the U.S., Canada,
the U.K., Germany, New Zealand, China, Japan, and Costa Rica
0.1
1
10
100
1000
0.1 1 10 100 1000
Observed N2O flux, kg N/ha/year
Mod
eled
N2O
flux
, kg
N/h
a/ye
ar
0.4
0.
0. 0.4
0.032
0.37
0.
0.
0.033
0.05
0.037
0.340.41
0.43
0.032
0.032
0.032
0.035
0.015
0.0350.029
0.035
0.028
0.011
0.031
0.05
0.0290.029
0.006
0.01
0.0190.019
0.02 0.025 0.025
0.010.015
R2 = 0.8366
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Model Evaluation
Coefficient of determination, R2
Provides a measure of how well future outcomes are likely to be predicted by the model (0-1)
Root mean square error (RMSE)A measure of the precision of the model in comparison with the field measurements. Units are the same as the model units.
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DNDC Validation1 to 1 line
0
10
20
30
40
50
0 10 20 30 40 50
Measured N2O (kg N-N2O/ha)
DN
DC
Mod
eled
N2O
Em
issi
ons
R-squared = 0.83RMSE = 8.9 kg N-N2O/han = 69
RMSE = 7.1 kg N-N2O/ha
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0
10
20
30
40
50
0 10 20 30 40 50
Measured N2O (kg N-N2O/ha)
DN
DC
Mod
eled
N2O
Em
issi
ons
Single site, R^2=0.83, RMSE=8.9Avg 2 sites, R^2=8.5,RMSE=5.6Avg 6 site, R^2=0.9,RMSE=2.8
Impact of Scale: Does the model perform better when we aggregate?
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Performance improves with aggregation
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 4 6 8 10 12Aggregation (# of observations/m odel)
Line
ar R
egre
ssio
n (R
-Squ
ared
)
0
2
4
6
8
10
12
RM
SE (k
g N
-N20
/ha)
R-squaredRMSE
…implications for use in protocols and for emission inventories.
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Future Validation: CA CropsOn-going projects collecting field measurements of N2O emissions:
UC Davis (Horwath, Six and Smart) and CSU Fresno (Goorahoo)Alfalfa, Almonds, Silage Corn, Cotton, Grapes (table and wine), Lettuce, Rice, Tomato and WalnutWill create an important validation dataset for CaliforniaFunding from ARB, CDFA, CEC and PackardTimeline: 2009 through 2012
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Using Model for Mitigating GHG Emissions :
Tomato ExampleSite: A tomato field at SAFS site in Davis, California
Simulated period: 1991-2000
Climate: Temperature 16°C, precipitation 210-630 mm
Soil: Silt loam, SOC 0.011 kg C/kg, pH 7.0
Tillage: Conventional
Fertilization: 150 kg urea-N/ha
Irrigation: Precision with drip or better spray method
DNDC as a Decision Support Tool…
…examine fertilizer practices (rate, depth, # applications)
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Biogeochemical models (DNDC) serve Applications for Defining Management Opportuntites for Mitigating GHG Emissions
A specific management alternative
Yield
C storage Trace gas
N leaching
Climate
Soil
Vegetation
Other management
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Impacts of Baseline vs. Management Scenarios on N2O Emission and Other C and N Fluxes for a Tomato Field
Baseline BMP Change rate
N2O(kg N/ha)
5.9 2.7 -54%
NH3(kg N/ha)
4.4 2.1 -52%
N leaching(kg N/ha)
56 21 -63%
Crop yield(kg DM/ha)
3718 3710 -0.2%
dSOC(kg C/ha)
-1470 -1472 +0.1%
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Discussion: Tomato Example
1. N2O emissions from agricultural soils can be reduced by up to 50% by adopting alternative fertilizing approaches;
2. Effectiveness of the alternatives varies with climate, soil and other management conditions (use GIS data as inputs);
3. Integrated model‐database tool can be integrated with other tools for spatially differentiated Carbon footprints and assessment of mitigation options.
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California rice case study:
Using DNDC for GHG inventory and assessing opportunities for reducing
GHG emissions.
NRCS, EDF and CRC Funding PIs: Eric Holst (EDF) and Paul Buttner (CRC)
Collaboration with UC Davis
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Project Goals: Use DNDC to define baseline net Greenhouse Gas Emissions
Baseline refers to current management practices, namely rice production during summer months with continuous flooding, followed by straw residue incorporation with winter flooding.
Use DNDC to assess opportunities for net GHG emission reductions through changes in residue, water and/or fertilizer management.Define protocol for carbon offsets.
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Background: GHG from RiceMethane (CH4) – produced by fermentation in anaerobic conditions (flooding), GWP = 25 (25 times more potent than CO2)
Dominant GHG in continuously flooded rice.
Nitrous Oxide (N2O) –produced by nitrification and denitrification (nitrate reduction), GWP = 298.
Minor GHG in continuously flooded rice
Carbon Dioxide (release of stored soil carbon –tillage) and soil carbon sequestration (storage of organic carbon in soils – crop residues).
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Step 1: Use GIS and Remote Sensing to Build GIS databases for California, USA
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Soils
Climate
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Agricultural Management MappingAgricultural Management Mapping• Crop type• Irrigation management• Crop calendar
o Multi‐temporal acquisition strategies enable mapping activity (planting, harvest, flooding, tilling…) dates
• Tillage practiceo Operational tillage mapping uses prior year (season) crop type and residue information in a decision tree framework to map tillage management
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June fine beamRGB (hh: hv: difference)
September fine beamRGB (hh: hv: difference)
GIS LULCRice: turquoise, Green: fruit trees
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Operational rice products• Hydroperiod• Crop calendar (DOY)• Planting dates• Parameterize models
Features• “now‐cast” ability; fully automated• 95%+ accuracy• multiscale (spatial & temporal)
• 6.25 m seasonal (PALSAR)• Moderate (Landsat/AWiFS)• 250m daily (MODIS)• 250m 8‐day (MODIS)
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Used Remote Sensing (PALSAR and MODIS) to map rice extent and water management –indentify baseline management.
~230,000 ha of rice (~500,000 acres)
Mapped duration of winter flooded
-few fields had standing water in April (likely due to precipitation)
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GIS Soils Databases
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Step 2: DNDC Model Testing for Methane from California Rice
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CH4 Model Validation: Rice
NB: No sites in California…
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Model Testing: Maxwell & RESTested DNDC against published data from a water management and residue management study at Maxwell, California.New data collected by Assa and Horwath at RESValidation data: CH4 emissions
Baseline management: straw incorporation with winter flooding for decompositionRemoval (burning) of straw residue with winter floodingIncorporation of straw without winter floodingDrill seeding
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Additional Rice Methane validation data for California
RES data: source Assa and Horwath, unpublished
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CH4 Model Validation: With CA Sites
Maxwell Data
RES Data
R2 = 0.85, n=9, CA Sites only
Added CA Rice Validation
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Step 3: Run DNDC Model for Baseline and Candidate Offset Management Practices for California, USA
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Rice Straw and Flooding Management
Baseline Management (current typical practices)
Water seeded, rice straw incorporated (15% burned), winter flooded (50-70%), tillage and fertilizer use (based on UCCE stats).
Alternative management to reduce GHGStraw removalNo winter floodingMid-season drainageDrill seeding
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Baseline and Straw Removal Results:
Spatially explicit DNDC-modeled CH4 emissions from CA rice fields with different water/residue management practices in 2004
Winter flooding +100% residue incorporation
Winter flooding + straw removal
0.09 Mt CH4-C 0.06 Mt CH4-C
Baseline emissions (~0.09 MMT CH4-C)Straw removal emissions (~0.06 MMT CH4-C)
Results are preliminary, finalResults in May 2010.
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GHG Reductions
SpatialVariability
Power of process model to capture spatial variability inenvironmental controls on Ch4 emissions.
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Methane Emissions from Rice: Comparison of Methods
US EPA Emission Factor: 210 kg CH4/ha/yrARB Emission Factor: 122 kg CH4/ha/yrDNDC Model: ~500 Kg CH4/ha/yr
Source of discrepancies?
CA Maxwell site has heavy soils (50% clay) and thus low emissions ~170 kg CH4/ha)
EFs do not include Winter floodingRES data (~450 kg CH4/ha, source: Assa and Horwath,
unpublished)
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Role of Remote Sensing…
Important for developing regional databases and for mapping and potentially monitoring management practices: for compliance, verification , or tracking sustainability…
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Agricultural Management MappingAgricultural Management Mapping• Crop type• Irrigation management• Crop calendar
o Multi‐temporal acquisition strategies enable mapping activity (planting, harvest, flooding, tilling…) dates
• Tillage practiceo Operational tillage mapping uses prior year (season) crop type and residue information in a decision tree framework to map tillage management
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Web-based Geospatial Tillage Mapping and Monitoring System
In development with NASA and USDA funding
Wood County, OH (Maumee River Watershed)23 May, 2006
R: SWIR, G: NIR, B: RED; Landsat TM 5
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Wood County, OH (Maumee River Watershed)23 May, 2006
High Crop Residue CoverCorn – No Till
R: SWIR, G: NIR, B: REDLandsat TM 5
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Wood County, OH (Maumee River Watershed)23 May, 2006
Mapping accuracies: 75%-85% on field basis.Higher for regional estimation.
Low Crop Residue Cover
Soy –Conventional
Till
R: SWIR, G: NIR, B: REDLandsat TM 5
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Conclusions…CH4 and N2O emissions from agricultural is a complex, driven by environmental condition, management and microbial processesProcess models are critical tools for developing GHG inventories and assessing options for reductionsRigorous validation is key…must rely on sound field measurements.Remote sensing has an important role for mappingand monitoring.Tools for tracking uncertainty: model structural and due to uncertainties in input conditions.
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Thank you!
Dr. William SalasApplied Geosolutions, LLC
87 Packers Falls RoadDurham, NH 03924 USA