1

Computation of Soil Organic Carbon Change for Agricultural Landscapes

of Canada

Computation of Soil Organic Carbon Change for Agricultural Landscapes

of Canada

Brian McConkey, Darrel Cerkowniak and NCGAVS teamMarch 11, 2010

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Carbon- CanadaCarbon- Canada

• Soil Organic C (SOC) and Sustainability

• Good indicator of soil quality

• Affects soil structure, water holding and movement, nutrient supplying power, cation exchange, support soil microbial community

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8

Organic C (%)

Pro

du

cti

vit

y (

Mg

ha

-1)

R2=0.70

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8

Organic C (%)

Pro

du

cti

vit

y (

Mg

ha

-1)

R2=0.70

• Important indicator under National Agri-Environmental Health, Analysis, and Reporting System (NAHARP)

• 2000, 2005, 2010 Agri-Environmental Indicator Reports

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Effect onatmospheric CO2

~Soil carbon

Initialcultivation

Soil CDecrease

Soil CStable

Soil CIncrease

Managementchange

agriculture

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Greenhouse Gas (GHG) Accounting

Greenhouse Gas (GHG) Accounting

• United Nations Framework Convention on Climate Change

• Report all GHG sources and removals

• Includes carbon change on all managed land

• Kyoto Protocol

• Like Convention except, for carbon change, only mandatory activity of afforestation, reforestation, and deforestation and the elected activity of cropland management

- ...the system of practices on land on which agricultural crops are grown and on land that is set aside or temporarily not being used for crop production.

• One with three other countries (Denmark, Spain, and Portugal) toelect reporting on cropland management

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Prairie farmer receiving payment for carbon offset from adoption of direct seeding – Heightened interest in Soil C

C-Green

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ComputationComputation

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Basic Computation MethodBasic Computation Method

• Annual C stock change = Activity x Emission/Removal Factor

• ΔΔΔΔC = A x F

• A=Activity: area (ha) of a land use management change or land use change on a particular soil that produces change in C stocks

• Examples: reduction in summerfallow frequency, clearing trees to increase agricultural land

• F=Annual C stock change factor (Mg ha-1) includes that in

• above-ground dead organic matter (identifiable plant or animal residues)

• soil organic C (below ground organic C that is not biomass or dead organic matter)

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C changes IncludedC changes Included

• C change only estimated for those Land Management Change (LMC) known to significantly affect C stocks and for which comprehensive time series of data exists

• Change in summerfallow area

• Change in area under different tillage systems

• Change in area of perennial vegetation

• Change in woody biomass of cropped vegetation

• C emissions also estimated for activities that are not LMC:

• Liming

• Cultivation of histosols

• C change also estimated for Land-Use Change (LUC):

• Forestland to Cropland

• Grassland to Cropland

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CanAG-MARS SchematicCanAG-MARS Schematic

Land Database -

Soil Landscapes of

Canada (SLC)

Agricultural

Activity Databases

+

Spatially referenced

land management

database

Carbon Factors –

Modelled and empirical

Time (yr)

101520253035

0 20 40 60 80

Ca

rbo

n (

t/h

a)

Activities linked

to C Factors

Reporting Zone

Accounting Unit(SLC polygon)

Nation

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C factorsC factors

• Much international C change accounting based on good knowledge of current and expected future C stocks under specific categories of agricultural activities

• This approach not well suited to Canada

- SOC data can be considered to represent circa 1975

- Much soil data collected focused on modal values from a soil development and taxonomic perspective, not necessarily from the perspective of modal value for a dynamic soil attribute such as SOC

• Therefore approach taken was to base accounting on relative C change due to change in management or land use

• Validated using comparative field studies

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Estimating FactorsEstimating Factors

1. Model-based factors

• The Century model of SOC processes has been shown to work well for Canadian situations

• Allows for consistent approach

• Century estimates the dynamics of C change that is difficult to determine from existing occasional observations of measured C change in field experiments

2. Factors scaled to match empirical observation

• Used where large number of observations that span several decades after land-use or management change- Summerfallow

- Grassland to cropland SOC

- Forestland to cropland SOC

• Used Century to derive dynamics

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Century ProcedureCentury Procedure

• Century sets starting values for the C pools based on generalized regional land use histories

• 90 years for initialization

• Robust, reproducible

• 10-yr Base Crop-Tillage System (CTS) produced

• Each crop and tillage system from Census representing about 10% of area included within input repeated 10-yr sequence

• Substitutions made to base CTS representing activities of interest

• e.g. no-till substituted for intensive till

• Difference between simulated SOC for base CTS and that for substituted CTS is fit to general first-order kinetics equation:

• ΔCLMC(t) = ΔCLMCmax [1-exp(-k*t)]

where

ΔCLMCmax = total C change from activity of interest

k = rate constant

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5000

5200

5400

5600

5800

6000

6200

6400

6600

0 10 20 30 40 50 60 70 80

Time (yr)

To

tal

So

il C

(g

m-2

)

CENTURY simulation of base CTS

CENTURY simulation of CTS with substitutions of

7 perennial crops for the 7 annual crops in base CTS

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CENTURY-simulated change in C

between base and substituted CTS

-200

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80

Time (yr)

∆C

(g

m-2

)

15

-500

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80

Time (yr)

∆C

LM

C (

g m

-2)

Fitted ∆CLMC(t) = ∆CLMCmax·[1- exp(-k·t)]

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FactorsFactors

• Factors were then averaged over reporting zones by general textural classes (coarse, medium, fine) for two reasons:

1. Over a reporting zone (“ecozone”), factors derived for soil components in SLC polygons represent a wide range of initial soil C states and combinations of management

• Average for reporting zone then represents a range of SOC and management situations such that would occur in an SLC polygon

2. Average across broad scales better representation of SOC than individual values for soil components in SLC polygons

• Similar averaging approach had been used in past to derive Canada’s soil organic carbon database

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Example Validation (Intensive to No-Till)Example Validation (Intensive to No-Till)

Empirical

0.06n/a-0.261Atlantic

0.100.140.063Ontario-Quebec

0.160.250.229Subhumid Prairies

0.110.150.05*8Semiarid Prairies

Inventory C change factor

(Mg ha-1 yr-1)

Standard

Deviation

(Mg ha-1 yr-1)

C change factor

(Mg ha-1 yr-1)Number of Field

StudiesRegion

*Conventional to No-Till (4 studies are Reduced to No-Till)

Source: VandenBygaart et al. 2008

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Features of Factor Derivation MethodFeatures of Factor Derivation Method

• Relative C change minimizes the effect of potentially incorrect initial SOC

• Initial SOC affects both base and substituted simulation similarly

• No C change without a change in land use or management

• Complex C change with time characterized by two parameters (ΔCLMCmax and k)

• Simple to calculate change over different periods to compare with C change factors from other sources

• Simple to scale ΔCLMCmax to observations if ΔCLMC known at specific

time

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CanAG-MARS SchematicCanAG-MARS Schematic

Land Database -

Soil Landscapes of

Canada (SLC)

Agricultural

Activity Databases

+

Spatially referenced

land management

database

Carbon Factors –

Modelled and empirical

Time (yr)

101520253035

0 20 40 60 80

Ca

rbo

n (

t/h

a)

Activities linked

to C Factors

Reporting Zone

Accounting Unit(SLC polygon)

Nation

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Cropland Management

in Canada

Cropland Management

in Canada

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Agricultural Management Information SourcesAgricultural Management Information Sources

• Census of Agriculture

• Most important

• Every farm enumerated

- Conducted every 5 years (2006 most recent)

- Information on crops, livestock, costs and returns, farming practices

• Land cover for remote sensing

• Annual agricultural production and inputs statistics (national, provincial, agricultural industry)

• Other farm surveys on farming practices

• Expert knowledge

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Canadian CircumstancesCanadian Circumstances

• Census data collected on administrative boundaries and converted to SLC polygon boundaries

• The concurrence of activities on same land not known

• Land areas can not be categorized into systems based on combination of C input and soil disturbance, etc.

• Land management changes only known on net area basis from area differences between Censuses

• Gross area changes to and from a practice may be lost in area of net change in that practice

• SLC polygon (typically about 10 000 ha) is smallest practical unit for which Canada can link soils and activity data

• SLC polygon scale best Canada can achieve for estimating C change on basis of gross area changes

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Land-Use Change (LUC)Land-Use Change (LUC)

• Grassland → Cropland

• From changes in area from Census with trends confirmed with remotely sensed data

• Forestland → Cropland

• Supplied by Canadian Forest Service National Forest Carbon – MARS (NFC-MARS)

• NFC-MARS also supplies change in biomass and dead organic matter for this land

• CanAG-MARS only calculates SOC change

• LUC on gross area basis

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Sink

Source

-15

-10

-5

0

5

10

15

20

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

C c

han

ge (

Mt

CO

2 )

Tree clearing to cropland

Land converted to cropland

Other land managementchange

Summerfallow

Tillage

Net

ResultsResults

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Predicted C StocksPredicted C Stocks

• SOC change provides an incomplete understanding of SOC as an indicator

• However absolute carbon stocks are difficult to interpret because vary hugely between soils due to soil forming factors regardless of recent land management

• Approach was to report a relative soil organic carbon (ROC)

• Reference was Century-modeled SOC under long-term grass that is extensively grazed without irrigation or fertilizer

• Not optimum or even particularly relevant but feasible and practical standard

• Arguably, SOC under long-term pasture is satisfactory in sense that neither deficient nor excessive for most agricultural activities

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The combination of declining SOC and low ROC is the most serious concern from a soil quality perspective

The combination of declining SOC and low ROC is the most serious concern from a soil quality perspective

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SummarySummary

• SOC is important soil attribute

• Become hugely important because of GHG concerns

• Canada has a computation method that is based on relative change in SOC

• Uses but does not depend on SOC data in Soil Landscapes of Canada Layer File

• Computation is based on factors of carbon change that were largely derived using Century model

• Canadian soils are net sink of 10 Mt CO2 in recent years

• Source in east and sink on prairies

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Acknowledgements

Denis Angers, Murray Bentham, Marie Boehm, Tony Brierley, Chang Liang, Pascale Collas, Henry de Gooijer, Ray Desjardins, Samuel Gameda, Brian Grant, Ted Huffman, Julian Hutchinson, Lance Hill, Paul Krug, Carlos Monreal, Tim Martin, Gary Patterson, Philippe Rochette, Ward Smith, Bert VandenBygaart, Xavier Vergé, Devon Worth