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

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

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

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

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

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

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

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

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

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

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

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

Measurements

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

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

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.

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.

Benchmark Buried Electromagnetic Marker N 5 m 1996 sampling

Measuring Soil Carbon is not easy!

Measurements vs. CENTURY

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

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

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)

Swift Current, SK, Canada

Swift Current, SK, Canada

Model vs. Measurement Swift Current, SK Rotation Tillage System 1986-98 SOC (Mg/ha/yr) 1999-2000 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

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

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

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