1. Determining Agricultural Soil Carbon Stock Changes in Canada
Brian McConkey*1, R. Lemke 1, B.C. Liang 2, G. Padbury 1, A. Frick 3, R. Desjardins 1, W. Lindwall 1
1 Agriculture and Agri-Food Canada
2 Environment Canada
3 Saskatchewan Crop Insurance Corporation

2. Outline
National Greenhouse Gas (GHG) Accounting System for Agriculture
Measurements from Prairie Soil Carbon Balance Study
CENTURY

3. Total Agricultural GHG Balances (full carbon accounting)
CH4
CO2
Soil organic matter N2
Fertilizer
Legumes
N2O

4. Canadian Accounting System for Agricultural GHG
(under development)
Models
C, N2O, (CH4)
Integration
Expert Systems
GHG flux and stock
Measurements
Landscape
Scaling-up
Land use & management
Describe farming systems
Weather,
Production
Databases
Verification
Strategies
Management-
Landscape Scenarios
National or
smaller
Agricultural
GHG Balances and Uncertainties
National or smaller

5. Outputs
National to farm-scale estimates of net GHG emissions and associated certainties from agriculture
Verification system design criteria
Standard methods for making and comparing measurements

6. Biophysical Models
Primary method of estimating GHG emissions and stock changes
Carbon (CENTURY)
N2O (DNDC & Expert N)
Methane (IPCC until better available)
Flexible for other models that can use minimum data set on soils, weather, management, etc.
Multi-scales
National, regional, … individual field
Reporting tool for inventories and predictive tool to assist policy development

7. Models continued
Transparent, consistent method to produce GHG estimates for different land use-management- climate-landscape situations
Cropland, rangeland, pasture, forage, orchards, etc.
Suitable for many combined land management changes
Once validated for full range of situations, most situations become essentially interpolation
Can use models with simplified general situations to derive IPCC-like coefficients that are easy to use

8. Land Use and Management
Land use and management by soil landscapes
Crop and pasture management
Fertilization rates and times
Irrigation amounts and times
Tillage operations and times
Manure application rates, forms, and times
Planting and harvest
Crop rotation, stand replacement
Grazing management
Production, yields

9. Landscape
Methodologies to scale up across landscapes, land uses, and land managements to produce large area estimates
From point model estimates or measurements to landscape
Reconcile modeled results with large area flux measurements
Strategies for modeling GHG on landscapes
Soil translocation
Soil water regimes

10. Landscape Effects 0-20 cm Soil C Mg/ha Tilled: 23 No-Till (10 yr) : 34
CENTURY
Predicted No-Till :
(Redistribution +
C dynamics) 33 29 41 40 48 47 53

11. Integration and Expert Systems
Automate accounting system
Integrate, complete, rationalize and simplify databases for input into models
Produce land use management histories (-100 to -50 yr to present)
Amalgamate model estimates and GHG coefficients to produce large-area or national estimates of agriculture GHG
Integrate uncertainty estimates from each factor to derive overall uncertainties of GHG emissions
Develop design criteria for a verification system that will meet the required acceptance standards
For crediting GHG mitigation actions accomplished on agricultural land

12. Canadian Accounting System for Agricultural GHG
(under development)
Models
C, N2O, (CH4)
Integration
Expert Systems
GHG flux and stock
Measurements
Landscape
Scaling-up
Land use & management
Describe farming systems
Weather,
Production
Databases
Verification
Strategies
Management-
Landscape Scenarios
National or
smaller
Agricultural
GHG Balances and Uncertainties
National or smaller

13. Measurements

14. Prairie Soil Carbon Balance Project (PSCB)
Objective:
Quantify and verify changes in soil C due to adoption of better agricultural management practices
Partnership:
Energy industry (GEMCo), Farmers (SSCA), and Governments

15. Measuring Changes in Soil C Stocks: Dealing with Variability
Account for topography
Carefully deal with surface litter and large roots
Account for differing soil density
Return to same small area (benchmark) for repeated measurements
Select benchmarks carefully
Take multiple soil samples

16. Benchmarks
Benchmarks established on 143 commercial fields that were converted to direct seeding in 1997
Change in soil C due to adoption of no-till + any associated decreases in fallow frequency
Sampled in fall 1996 and 1999, greatest value if sampled again in 3 to 5 years
Return to the same small benchmark to measure changes in soil C to minimize effect of inherent spatial variability.
Benchmarks selected carefully within field so no atypical variation within the benchmark.

17. Network Hierarchical Level 1 Level 2 Level 3
Change in SOC over time in direct seeded field
115 fields, only SOC measurements
Level 2
Retains 1-3 ha tilled strip
22 fields, biomass at harvest measured
Level 3
Landscape effects
6 fields, many intense measurement of crop and soil.

19. Benchmark Buried Electromagnetic Marker N 5 m 1996 sampling

20. Measuring
Soil Carbon
is not easy!

21. Measurements vs. CENTURY

22. Measured Results
C change
NT = 175 g C/m2
CT = 73 g C/m2
(crop-fallow to cont. crop)

23. CENTURY vs. Measured performance (1997-99)
Prairie
Climate
Measured
Mean (t C/ha)
CENTURY
Semiarid
0.71
0.92
Subhumid
1.25
0.90
All
1.01
0.91

24. Measurements suggests not:
Were SOC increases from adoption of direct seeding simply Fragile partially decomposed plant materials?
Measurements suggests not:
C:N ratio dropped by 0.19 units from 1996 to 1999 (P<0.05)
Light-fraction C for direct seeded, measured on level 2 sites only, dropped by 18% from 1996 to 1999 (P<0.05)

25. Swift Current, SK, Canada

26. Swift Current, SK, Canada

27. Model vs. Measurement Swift Current, SK
Rotation
Tillage
System
SOC
(Mg/ha/yr)
N2O
(Kg N/ha/yr)
Meas.
CENTURY
DNDC
Annual
Wheat
No-Till
0.04
0.14
0.2
0.7
Tilled
0.23
0.17
0.1
0.6
Fallow-
-0.13
-0.17
-0.08
-0.20

28. Deficiencies
GHG Model may be inadequate in capabilities where non-GHG models are good
Plant production, soil temperature, soil moisture, etc.
Erosion not well quantified on all landscapes
Tillage, wind, water
Fate of C & N in soil transported off site
Limited GHG measurements for some important situations to evaluate and improve models
Example: Grazing land
Need better description of processes to improve models
Example: reduced tillage

29. Summary
Biophysical models will be central to Canadian accounting systems for agricultural GHG
Derive GHG coefficients (useful for economic models and to deal with large inter-annual variation)
Report emissions
Predict effects of policy changes
Reward on-farm GHG mitigation actions (“Green Cover”)
Measurements of GHG is important
Evaluating and improving models
Verification strategies
Biophysical models can work satisfactorily
Accuracy can be very poor
Will be improving

30. Thank you