Monitoring, reporting, and verification of soil carbon sequestration on the cropland and grassland

of Canada

Brian G. McConkey, Denis Angers, Darrel Cerkonwiak, Émilie Maillard, and Jianling Fan

Agriculture and Agri-Food Canada*brian.mcconkey@agr.gc.ca

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C Stock Changes - Cropland

• Needed reproting system for Soil Organic Carbon (SOC) change consistent with Canadian circumstances

1) Limited high quality SOC data since much of that data collected at course resolution (1:100 000 maps) up to 70 years ago and SOC values have not been updated nor are there plans to update

2) No detailed knowledge of crops or farm practices on spatially explicit basis so agricultural activity had to be based on survey data

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Basic Calculation Method

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

• Annual C stock change includes that in – Litter (above-ground dead organic matter)– Soil Organic C (below ground organic C that is not biomass or coarse woody roots)– Woody biomass

• Activity is the area 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

• Emission/Removal Factor is a coefficient of annual change in C stocks per unit area of the activity

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Land Database - Soil Landscapes of

Canada (SLC)

AgriculturalActivity Databases

+

Spatially referenced land management database

Carbon Factors – Modelled and empirical

Time (yr)

101520253035

0 20 40 60 80

Car

bon

(t/ha

)

Activities linked to C Factors

Reporting Zone

Accounting Unit(SLC polygon)

Nation

Canadian System Schematic

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C 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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Land Database - Soil Landscapes of

Canada (SLC)

AgriculturalActivity Databases

+

Spatially referenced land management database

Carbon Factors – Modelled and empirical

Time (yr)

101520253035

0 20 40 60 80

Car

bon

(t/ha

)

Activities linked to C Factors

Reporting Zone

Accounting Unit(SLC polygon)

Nation

Canadian System Schematic

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C Factor Derivation Method

• C change estimated with and without land management change using the well validated Century model of SOC processes.

• The C Factor is derived from the difference• Features

– Initial (inaccurate?) SOC affects simulation with and without land management change similarly

– (well suited for offset quantification and factors used for such in Canada)– Factors transparent and comparable – Consistent approach– No C change without a change in land use or management

• Consistent with Tier 1 approach of IPCC Good Practice Guidance for LULUCF– Complex C change with time characterized by two parameters (ΔCmax and k)

• ΔC = ΔCmax x [1 – exp(-k x t)]• Simple to calculate change over different periods to compare with C change

factors from other sources• Simple to scale ΔCmax to observations if ΔC known at specific time

Estimating carbon change for cropland is really based on management practices

Canadian C Stock Changes By Type of Practices

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10

Effect of changing C input from crops is not currently included

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1.5

2.0

2.5

3.0

1975 1980 1985 1990 1995 2000 2005 2010 2015

C in

put (

Mg/

ha)

C inputTrend

*Trend: 5-year moving average of average Canadian crop C input

C input change for different crops

Canola &mustard

Winter wheat& fall rye

SOC change on grassland

• Grazing management on grasslands is complex and changes depending on annual situation – not easily categorized.– Practice-based estimates not workable.

• SOC not clearly related to vegetation condition due to species shift.• SOC increasing by 19* to 72** kg C/ha/yr by grazing compared with

nonj grazed controls.• Monitor SOC directly?

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*Wang et al. 2014. Rangeland Ecol. and Manage. **Wang et al. 2016. Sci.Reports,

Difficult to detect small C change on grasslands using soil measurements

Detectable SOC difference for grasslands as a function of sample size, grassland area, and depth of measurement (adapted from Maillard et al., 2017. Agriculture, Ecosystems, and Environment, DOI: 10.1016/j.agee.2016.11.024).

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Use of Vegetation Condition to Estimate C change of grassland?

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 20123000

3500

4000

4500

5000

5500

Growing Season Average NDVI for Pastures and Grasslands in Saskatchewan

NDVI-PastureLinear (NDVI-Pasture)NDVI-Grassland

ND

VI

• E.g. Normalized Difference Vegetation Index (NDVI) shows increasing grassland “greeness” over time consistent with generally increasing SOC

Li et al. 2013. J. Remote Env.

Discussion and Summary

• Developing factors of SOC change from modelling is very workable and useful where SOC is not intensely monitored– Need to maintain a network of long-term field experiments for validation– Increases to SOC on cropland is important in Canada– Improvements underway to include effect of changing C input from crops.

• Estimating SOC change on grasslands is challenging because grazing system complex compared to cropland– Currently Canada reports grassland SOC not changing although empirical

evidence that it could be increasing due to recovery from more degraded states that existed in first half of 20th century

– Measuring SOC change directly infeasible on national basis for estimating changes for < 20 yrs?

– Practical C monitoring system based on plant growth condition-SOC relationships?

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Grazie