Philippe Rochette, AAFC Québec AAFC Québec CityCity

Research on gaseous emissions Research on gaseous emissions from agricultural soils at the from agricultural soils at the

Québec City AAFC research centreQuébec City AAFC research centre

Soil respiration

Soil org. C

oldrecent

Plant roots

Soil respiration is the sum of several CO2 sources

Soil inorg. C

carbonates

CO2

Natural Abundance of Natural Abundance of 1313CC

• About 1.1‰ of atmospheric COAbout 1.1‰ of atmospheric CO22 is is 1313COCO2 2 (-(-8‰)8‰)

• Greater discrimination against Greater discrimination against 1313COCO22 by by Rubisco than by PEP carboxylaseRubisco than by PEP carboxylase

• More More 1313C in C4 (-12‰) than in C3 plants (-C in C4 (-12‰) than in C3 plants (-26‰)26‰)

C3 Soil org. C CO2

-26‰

CO2

-12‰

1 > Rrh,frac. > 0

Rhisophere RespirationRhisophere RespirationRochette and Flanagan,1997; Agron. J.Rochette and Flanagan,1997; Agron. J.

Rochette, Flanagan and Gregorich,1999; Agron. J.Rochette, Flanagan and Gregorich,1999; Agron. J.

C4 plant

Rrh = Rtot x Rrh,frac.

-12‰ > 13CO2 > -26‰

C3Soil org. CCO2

-26‰

13CO2 = -26‰

Contribution of corn-C to soil COContribution of corn-C to soil CO22

-10

-5

0

5

10

15

20

25

30

35

40

140 160 180 200 220 240 260 280 300 320

DAY OF YEAR

10 cm

20 cm

40 cm

RH

IZO

SP

HE

RE

/ T

OT

AL

RE

SP

IRA

TIO

N (

%) 0>Rrh,frac<1

Separation of soil respiration Separation of soil respiration into corn and native C sourcesinto corn and native C sources

-2

0

2

4

6

8

140 190 240 290 340DAY OF YEAR

CO

2 E

MIS

SIO

NS

(g

m-2

d-1

) total

rhizosphere

native CRt

Rrh

Rs

-1

1

3

5

7

9

11

13

15

0 5 10 15 20 25 30

SOIL TEMPERATURE (C)

CO

2 E

MIS

SIO

NS

(g

m-2

d-1

)

Rt = 5,23 x 1,99 (Ts-10)/10

r2 = 0,87

n = 20

Oxydation de la matière organiqueOxydation de la matière organiqueQQ1010 = 2 = 2

1 > Rres,frac. > 0

Maize residue Maize residue decompositiondecomposition

Rochette, Angers and Flanagan,1999; Soil Sci. Soc Am. J.Rochette, Angers and Flanagan,1999; Soil Sci. Soc Am. J.

Rres = Rtot x Rres,frac.

-12‰ > 13CO2 > -26‰

C3Soil org. CCO2

-26‰

13CO2 = -26‰

C3 plant

CO2

-12‰C4 residueC3 Soil org. C CO2

-26‰

0

0.1

0.2

0.3

0.4

0.5

0.6

120 170 220 270 320

DAY OF YEAR 1997

RE

SID

UE

CO

NT

RIB

UT

ION

MOLDBOARD

NO-TILL

May June July August September October

Contribution of the decompositionContribution of the decomposition of maize residues to total soil CO2of maize residues to total soil CO2

0>Rres,frac<1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

120 170 220 270 320

DAY OF YEAR 1997

CO

RN

-C L

OS

SE

S (

g C

m-2

d-1

) MOLDBOARD

NO-TILL

May June July August September October

Decomposition rates of maize residuesDecomposition rates of maize residues

Rres=Rt x Rres,frac

Chamber measurements of soil Chamber measurements of soil NN22O emissions: Are they O emissions: Are they

reliable?reliable?Rochette and Eriksen-Hamel (2008)

ObjectivesObjectives

• Determine Determine criteriacriteria for assessing the quality for assessing the quality of soil Nof soil N22O flux measurements made using O flux measurements made using NFT-NSS chambersNFT-NSS chambers

• Apply these criteria to Apply these criteria to evaluateevaluate chamber chamber methodologies used in the scientific methodologies used in the scientific literatureliterature

• Propose a Propose a minimum set of criteriaminimum set of criteria for NFT- for NFT-NSS chamber methodology for the NSS chamber methodology for the measurement of soil Nmeasurement of soil N22O fluxO flux

Definition of CriteriaDefinition of Criteria

• CriteriaCriteria to evaluate NFT-NSS chamber to evaluate NFT-NSS chamber methodology were determined based on:methodology were determined based on:

• Hutchinson and Livingston, 1993Hutchinson and Livingston, 1993• Livingston and Hutchinson, 1995Livingston and Hutchinson, 1995• Holland et al., 1999Holland et al., 1999• Hutchinson and Livingston, 2002Hutchinson and Livingston, 2002• Davidson et al., 2002Davidson et al., 2002• Smith and Conen, 2004Smith and Conen, 2004• Rochette and Hutchinson, 2005Rochette and Hutchinson, 2005• Rochette and Bertrand, 2007Rochette and Bertrand, 2007

DatasetDataset

• Chamber methodology was evaluated on Chamber methodology was evaluated on a sample of the a sample of the 362 studies362 studies reporting soil reporting soil NN22O emissions measured using NFT-NSS O emissions measured using NFT-NSS chambers. Selected studies were from:chambers. Selected studies were from:

• Stehfest and Bouwman, 2006Stehfest and Bouwman, 2006• Jungkunst et al., 2006Jungkunst et al., 2006• Lu et al., 2006Lu et al., 2006• Survey of recent literatureSurvey of recent literature

NFT-NSS chamber design and NFT-NSS chamber design and methodologymethodology

Soil surface

Soil

Gasket

Anchor

Fastener

Sampling port

Venting tubeInsulation

14 cm

10 cm

4 cm

Soil surface

Soil

Gasket

Anchor

Fastener

Sampling port

Venting tubeInsulation

14 cm

10 cm

4 cm

Deployment time (min)

0 5 10 15 20 25

Headspace N

2O

concentration (µmol m

ol-1

)

0

2

4

6

8

10

y = 0.345x + 0.735

r2 = 0.984dG/dt = 0.345 µmol mol-1 min-1

y = -0.0065x2 + 0.482x + 0.407

r2 = 0.998

dG/dt = 0.482 µmol mol-1 min-1N2O

con

cent

ratio

n

FN2O = dC/dt • V/A • Mm/Mv • (1-e/P)

NL/L: 0.48/0.35 = 1.4

CharacteristicsCharacteristics for evaluating for evaluating NFT-NSS chamber methodologyNFT-NSS chamber methodology

• Characteristics are simple descriptive Characteristics are simple descriptive criteria grouped in two types:criteria grouped in two types:

•BinaryBinary ("yes or no“ type) ("yes or no“ type)•NumericalNumerical (“quantitative” (“quantitative” (cm, cm(cm, cm22, cm, cm33, ,

min, …)min, …) ) )

NFT-NSS Chamber NFT-NSS Chamber ScoringScoring of of Binary CharacteristicsBinary Characteristics

CharacteristicCharacteristic

(Score)(Score)

Chamber type (2 pces)Chamber type (2 pces)

InsulationInsulation

VentVent

Press. air samplesPress. air samples

QC air sampleQC air sample

Non linear dC/dtNon linear dC/dt

T correctionsT corrections

""0 slope0 slope"" tested tested

Sample vialSample vial

Very poorVery poor PoorPoor GoodGood Very GoodVery Good

(0)(0) (1)(1) (2)(2) (3)(3)

nono yesyes

nono yesyes

nono yesyes

nono yesyes

nono yesyes

nono yesyes

nono yesyes

nono yesyes

Plastic Plastic syringesyringe

Glass syringeGlass syringe All other vialsAll other vials Exetainers, Exetainers, vacutainers, vacutainers,

etc.etc.

NFT-NSS ChamberNFT-NSS Chamber Scoring Scoring of of Numerical CharacteristicsNumerical Characteristics

CharacteristicCharacteristic

(Score)(Score)

Chamber height (cm)Chamber height (cm)

Chamber base insertion (cm / hr)Chamber base insertion (cm / hr)

Deploy. Duration (min)Deploy. Duration (min)

# of air samples# of air samples

Air sample storage duration (days)Air sample storage duration (days)

Very poorVery poor PoorPoor GoodGood Very goodVery good

(0)(0) (1)(1) (2)(2) (3)(3)

≤≤55 >5 - 10>5 - 10 >10 - 20>10 - 20 >20>20

< 5< 5 5 - <85 - <8 8 - <128 - <12 ≥≥1212

>60>60 >40 -60>40 -60 >20 - 40>20 - 40 ≤≤2020

11 22 33 >3>3

Plastic Plastic syringesyringe

>2>2 1 - 21 - 2 ≤≤11

Glass Glass syringesyringe

>4>4 >2 - 4>2 - 4 1 -21 -2 ≤≤11

othersothers >90>90 >45 - 90>45 - 90 > 15 - 45> 15 - 45 ≤≤1515

Minimum Standards for NFT-NSS ChambersMinimum Standards for NFT-NSS Chambers

• Use insulated and vented “base-and-collar” Use insulated and vented “base-and-collar” chamberschambers

• Avoid chamber heights < 10 cmAvoid chamber heights < 10 cm• Insert to ≥ 5 cmInsert to ≥ 5 cm• Use pressurized fixed-volume containers of Use pressurized fixed-volume containers of

known efficiency for air sample storageknown efficiency for air sample storage• Include a minimum of three discrete air samples Include a minimum of three discrete air samples

during deployment; including one at time=0during deployment; including one at time=0• Test non-linearity of changes in headspace Test non-linearity of changes in headspace

concentration with time for estimating dC/dt at concentration with time for estimating dC/dt at time=0time=0

Measurement of Soil NMeasurement of Soil N22O O EmissionsEmissions

• > 600 reports in literature since 1980> 600 reports in literature since 1980

• MethodologyMethodology– Steady-state chambers (open)Steady-state chambers (open)– Non steady-state chambers (closed)Non steady-state chambers (closed)– Soil profileSoil profile– Micrometeorological methodsMicrometeorological methods

• > > 98% measured using non flow-through non 98% measured using non flow-through non steady-state chambers (NFT-NSS)steady-state chambers (NFT-NSS)

• National GHG inventories (IPCC) and model National GHG inventories (IPCC) and model calibration are based on chamber calibration are based on chamber measurementsmeasurements

Number of Characteristics Number of Characteristics ReportedReported

Pro

port

ion o

f st

ud

ies

(%)

0

25

50

75

100

All years

< 4 4 to 7 8 to 11 12 to 15

<4

4 to 7

8 to 11

12 to 15

36% of the studies reported < half of the characteristics

Binary CharacteristicsBinary Characteristics

CharacteristicCharacteristic Proportion of studies Proportion of studies reporting the use of reporting the use of each characteristiceach characteristic

(%)(%)

Chamber typeChamber type 9191

Time zero sampleTime zero sample 6666

InsulationInsulation 4949

VentVent 4747

Press. air samplesPress. air samples 3535

T correctionsT corrections 3333

QC air sampleQC air sample 1717

Non linear dC/dtNon linear dC/dt 1515

““zero slope“ zero slope“ testedtested

55

Only 4 characteristics are reported in >50% of the studies

Numerical CharacteristicsNumerical CharacteristicsPro

port

ion o

f st

ud

ies

(%)

0

25

50

75

100

Quality of air samplevials

Chamber baseinsertion

Number of samplestaken

Duration of sampling

No Data Very Poor Poor Good Very Good

About 1 out of 2 studies uses poor chamber insertion depth, air sample handling and chamber deployment duration

Pro

port

ion o

f st

ud

ies

(%)

FactorsFactors

0

25

50

75

100

Design of Chamber Seal on Soil Sample Handling andStorage

Determination of dC/dt

No Data Very Poor Poor Good Very Good

• Good chamber design• Poorly used …

NFT-NSS Chamber MethodologyNFT-NSS Chamber Methodology Confidence Level (% error)Confidence Level (% error)

• High (<10%)High (<10%)• No No poorpoor or or very poorvery poor factors factors

• Medium (<30%)Medium (<30%)• ≤≤2 2 poorpoor and no and no very poorvery poor factors factors

• Low (10 – 50%)Low (10 – 50%)• ≥≥3 3 poorpoor factors factors• 1 1 poorpoor and 1 and 1 very poorvery poor factors factors

• Very Low (20 – 60%)Very Low (20 – 60%)• ≥≥2 2 poorpoor factors and 1 factors and 1 very poorvery poor factors factors• >2 >2 very poorvery poor factors factors

Level of Confidence in NFT-NSS measurementsLevel of Confidence in NFT-NSS measurementsPro

port

ion o

f st

ud

ies

(%)

Time Intervals

0

25

50

75

100

1978-1989 1990-1994 1995-1999 2000-2004 2005-2007 All years

Very low Low Medium High

Confidence is low in the N2O flux reported by 60% of studies

ConclusionsConclusions

• Confidence in soil NConfidence in soil N22O fluxes was estimated as low or O fluxes was estimated as low or very low in 60% of the 362 studiesvery low in 60% of the 362 studies

• This proportion was 50% in recent studies (2005-07)This proportion was 50% in recent studies (2005-07)

• Causes for poor scores: Causes for poor scores: • incomplete description of methodologyincomplete description of methodology• plastic syringesplastic syringes• shallow insertionshallow insertion• low number of air sampleslow number of air samples

• Greater effort is required to adopt and report more Greater effort is required to adopt and report more rigorous methodologyrigorous methodology

• Greater vigilance by reviewers and editorsGreater vigilance by reviewers and editors