Sequestering and Measuring Soil Carbon:

Prairie Soil Carbon Balance Project

Brian McConkey1 *, Chang Liang2,, Glenn Padbury1, Arlan Frick3 ,Wayne Lindwall1

1Agriculture and Agri-Food Canada, 2Environment Canada, 3formerly University of Saskatchewan, currently Saskatchewan Crop Insurance Corporation *mcconkeyb@em.agr.ca

Soil Carbon “Soil at Risk” (1984) identified

depleting soil organic matter as one of three major threats to Canada’s soils (with erosion and salinization) Programs initiated to promote

practices like no-till and reduced fallow to increase soil organic matter

Soil organic carbon key indicator of the soil health

Soils Sinks Practices that increase soil carbon are those

that accomplish soil conservation and increase efficiency and effectiveness of using available water resources Reduced tillage and direct seeding Increasing plant production

Irrigation, Improved nutrient supply, Better adapted and more productive varieties, Improved grazing strategies

Reducing summerfallow Organic C additions

Cover crops, Green manures, Compost, Animal manures

Soil Sinks Have Many Benefits Better environment

Water quality Air quality Soil quality Biodiviersity

Consistent with Adaptation for Climate Change Practices that conserve soil and make more efficient and

effective use of water Thinking of the soil-plant-animal system as an ecosystem

Net emission reduction until GHG cleaner technologies

Sustainable development goals

Quantification and Verification Essential to reward removal of

atmospheric CO2

Reward good land stewardship Importance to acceptance

Prairie SoilCarbon Balance Project (PSCB)

Objective:Quantify and verify changes in soil

C due to adoption of better agricultural management practices

PSCB - Components Perennial Cropping (Forage)

C change due to better management of tame and native forage stands

Annual Cropping C change due to adoption of direct seeding

and reduced fallow Scaling Up

Technology to scale up from point estimates to regional estimates

PSCB - Who Research:

AAFC (Brandon, Swift Current, Lethbridge) Universities of Manitoba, Saskatchewan, Alberta Alberta Agriculture, Food, and Rural Development Saskatchewan Soil Conservation Association

Funding Support: GEMCo TransAlta Utilities AAFC Matching Investment Initiative Canadian Cattleman’s Association Ducks Unlimited

Develop estimates for rate of C sequestration Research Experiments Medium- and long-term paired farm

comparisons Modelling C change (CENTURY model

of C dynamics) Establish benchmark

verification/auditing system on commercial farm fields Ability to detect C change over 3 yr?

PSCB Annual Cropping What

C Sequestration Coefficients

(tonne C/ha per yr)

PrairieClimate

Soil Texture

Sandy Loamy Clayey

Semiarid 0.1 0.2 0.3

Subhumid

0.2 0.3 0.4

Eliminate Fallow C Gains(tonne C/ha/yr)

0.150.3Subhumid

0.10.2Semiarid

Fallow 1 yr in 4

Fallow 1 yr in 2

Prairie Climate

Crop Rotation

Soil C Model

GIS

BenchmarkedFarm Fields

Soil, Weather, & Management Databases

Basic Research/Plot Measurements

Verification

Soil C modelParameterization

Land-FarmingSystem-WeatherSituations

Large-area orNational Soil CStock Changes

Auditing

Outline ofPrairie Soil

Carbon BalanceProject

Remote Sensing/Flux Measurements

(Future)

NATIONAL SOILSCOVERAGE

SOIL LANDSCAPES OFSASKATCHEWAN

SOIL LANDSCAPE POLYGONS

SOIL LANDSCAPE

SOIL PROFILE

Measurement of soil C gain

0

10

20

30

40

50

60

70

80

Initial

Increase with improved management

Variability from completely random

sampling

Soil C

(to

nn

e C

ha

-1)

(hypothetical example)

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.

Verification SitesSaskatchewan

CANADAJune, 1997

56

48

42

34

14

10

4

21226142630

2

4

6

16

18

28

58

60

1996 sampling

1999 sampling

N

2 m

BuriedElectromagneticMarker

5 m

Benchmark

Outline ofPrairie Soil

Carbon BalanceProject

Soil C Model

GIS

BenchmarkedFarm Fields

Soil, Weather, & Management Databases

Basic Research/Plot Measurements

Verification

Soil C modelParameterization

Land-FarmingSystem-WeatherSituations

Large-area orNational Soil CStock Changes

Auditing

Remote Sensing/Flux Measurements

Results

Crop Yields from 22 PSCB Fields with Tilled Strip

Retained

0

1

2

3

4

5

6

7

Dry Matter Yield

(tonne/ha)

Above-groundBiomass

Grain Above-groundResidue

No-TillTilled

*

*

*Tilled less than direct seeded at confidence of 95%

MeasuringSoil Carbon

2 m

5 m

Small-scale0-10 cm SOC

Variability

Surface Residue

Creates Many Sampling Problems Additional C sink

Amount variable with time and from field to field

No-till residue sink typically from 0.1 up to 2.0 tonne C/ha more than same sink in conventionally tilled systems in Saskatchewan (usually less than 0.3 tonne C/ha more no-till)

Creates Many Sampling Problems Additional C sink

Amount variable with time and from field to field

No-till residue sink typically from 0.1 up to 2.0 tonne C/ha more than same sink in conventionally tilled systems in Saskatchewan (usually less than 0.3 tonne C/ha more no-till)

Results for Fields Converted to Direct Seeding in 1996(t C/ha)

Expected C Gains from 1996-1999

Measured 0-20 cm C Gains from 1996-

1999

1.16 1.01

•Includes decrease in fallow (occurred in majority of fields converted)

•Measured change significant (95% confidence)

CENTURY vs. Measured performance (1997-99)

PrairieClimate

MeasuredMean (t C/ha)

CENTURYMean (t C/ha)

Semiarid 0.71 0.92

Subhumid 1.25 0.90

All 1.01 0.91

Variability Benchmarks reduced but did not

eliminate variability Measured SOC changes have to be

treated statistically Results for benchmark on individual field

can’t usually be meaningfully interpreted Cost-effective verification systems will

probably involve 10-20 benchmarked fields over large areas of similar soil-climate-management situations

Measurement Issues Careful measurement of SOC

critical to verification Need for certification from unbiased

party or international team of experts?

5 years practical minimum for measuring SOC change

5 yr is Kyoto commitment period for which greenhouse gas emission reduction targets apply

Sink – Asset or Liability? Sink is the verb

Credit giving for the process of removing CO2 from atmosphere

Stock is the noun No credit for CO2 already sunk into a C stock 2-3% decrease in prairie agricultural soil stock

would release CO2 equal Canada’s 1990 emissions (CO2equivalent)

Should be liable for release from the stock regardless of whether part of the stock was used a credited sink

Full Carbon Accounting Canada obligated to report all CH4 and N2O

emitted from agricultural soils Also reports CO2 emitted from agricultural soils

Ecological common sense to also report removals of CO2 into soil where occurring Ag soils will still be net emitter in CO2 equivalents on

national basis Ag soil sinks

Included in national estimates whether farmer rewarded for practice or not

Once reported farmer can not take it back Agriculture liable for releases of ag soil C

Soil Carbon is Part of Whole Greenhouse Gas Budget Soil C quantification and verification

system will become part of comprehensive greenhouse gas farm budget of CO2, CH4, and N2O Biofuels C sequestered in building products Livestock

Manure Feeds

Have to Consider Greenhouse Gas Budget in a Farming System

CH4

CO2

Soil organic matter

N2

Fertilizer

Legumes

N2O

Summary Agricultural ag soil sinks have many benefits

Measurement and verification is essential to acceptance and value of agricultural soil sinks

Prairie Soil Carbon Balance Project demonstrated a practical and cost-effective system for quantifying and verification of SOC changes

Indicated many opportunities for improvements in measurement and modeling

Cost-effective verification systems will likely pool SOC changes over large areas

Need to start thinking less of C sequestration alone and more about entire farm greenhouse gas budget