Determining Agricultural Soil Carbon Stock Changes in Canada

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 *mcconkeyb@em.agr.ca 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. Fertilizer Legumes N2 N2O CH4 CO2 Soil organic matter Total Agricultural GHG Balances (full carbon accounting)

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

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

13. Measurements

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

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 • 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. Buried Electromagnetic Marker N 5 m 1996 sampling 1999 sampling 2 m Benchmark

20. Measuring Soil Carbon is not easy!

21. Measurementsvs.CENTURY

22. Measured Results 1996-99 C change NT = 175 g C/m2 CT = 73 g C/m2 (crop-fallowto cont. crop)

23. CENTURY vs. Measured performance (1997-99)

24. 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. MeasurementSwift Current, SK

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