1. AAFC Québec City Philippe Rochette, AAFC Québec City Research on gaseous emissions from agricultural soils at the Québec City AAFC research centre

2. Soil respiration Soil org. C old recent Plant roots  Soil respiration is the sum of several CO 2 sources Soil inorg. C carbonates CO 2

3. Natural Abundance of 13 C About 1.1‰ of atmospheric CO 2 is 13 CO 2 (-8‰)About 1.1‰ of atmospheric CO 2 is 13 CO 2 (-8‰) Greater discrimination against 13 CO 2 by Rubisco than by PEP carboxylaseGreater discrimination against 13 CO 2 by Rubisco than by PEP carboxylase More 13 C in C4 (-12‰) than in C3 plants (-26‰)More 13 C in C4 (-12‰) than in C3 plants (-26‰)

4. C 3 Soil org. C CO 2 -26‰ CO 2 -12‰ 1 > R rh,frac. > 0 Rhisophere Respiration Rochette and Flanagan,1997; Agron. J. Rochette, Flanagan and Gregorich,1999; Agron. J. C 4 plant R rh = R tot x R rh,frac. -12‰ >  13 CO 2 > -26‰ C 3 Soil org. C CO 2 -26‰  13 CO 2 = -26‰

5. Contribution of corn-C to soil CO 2 -10 -5 0 5 10 15 20 25 30 35 40 140160180200220240260280300320 DAY OF YEAR 10 cm 20 cm 40 cm RHIZOSPHERE / TOTAL RESPIRATION (%) 0>R rh,frac <1

6. Separation of soil respiration into corn and native C sources RtRt R rh RsRs

7. Oxydation de la matière organique Q 10 = 2

8. 1 > R res,frac. > 0 Maize residue decomposition Rochette, Angers and Flanagan,1999; Soil Sci. Soc Am. J. R res = R tot x R res,frac. -12‰ >  13 CO 2 > -26‰ C 3 Soil org. C CO 2 -26‰  13 CO 2 = -26‰ C 3 plant CO 2 -12‰ C 4 residue C 3 Soil org. C CO 2 -26‰

9. Contribution of the decomposition of maize residues to total soil CO2 of maize residues to total soil CO2 0>R res,frac <1

10. Decomposition rates of maize residues R res =R t x R res,frac

11. Chamber measurements of soil N 2 O emissions: Are they reliable? Rochette and Eriksen-Hamel (2008)

12. Objectives Determine criteria for assessing the quality of soil N 2 O flux measurements made using NFT- NSS chambersDetermine criteria for assessing the quality of soil N 2 O flux measurements made using NFT- NSS chambers Apply these criteria to evaluate chamber methodologies used in the scientific literatureApply these criteria to evaluate chamber methodologies used in the scientific literature Propose a minimum set of criteria for NFT-NSS chamber methodology for the measurement of soil N 2 O fluxPropose a minimum set of criteria for NFT-NSS chamber methodology for the measurement of soil N 2 O flux

13. Definition of Criteria Criteria to evaluate NFT-NSS chamber methodology were determined based on:Criteria to evaluate NFT-NSS chamber 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

14. Dataset Chamber methodology was evaluated on a sample of the 362 studies reporting soil N 2 O emissions measured using NFT-NSS chambers. Selected studies were from:Chamber methodology was evaluated on a sample of the 362 studies reporting soil N 2 O emissions measured using NFT-NSS 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

15. NFT-NSS chamber design and methodology N 2 O concentration F N2O = dC/dt V/A M m /M v (1-e/P) NL/L: 0.48/0.35 = 1.4

16. Characteristics for evaluating NFT- NSS chamber methodology Characteristics are simple descriptive criteria grouped in two types:Characteristics are simple descriptive criteria grouped in two types: Binary ("yes or no“ type)Binary ("yes or no“ type) Numerical (“quantitative” (cm, cm 2, cm 3, min, …) )Numerical (“quantitative” (cm, cm 2, cm 3, min, …) )

17. NFT-NSS Chamber Scoring of Binary Characteristics Characteristic (Score) Chamber type (2 pces) Insulation Vent Press. air samples QC air sample Non linear dC/dt T corrections "0 slope" tested Sample vial Very poor PoorGood Very Good (0)(1)(2)(3) noyes noyes noyes noyes noyes noyes noyes noyes Plastic syringe Glass syringe All other vials Exetainers, vacutainers, etc.

18. NFT-NSS Chamber Scoring of Numerical Characteristics Characteristic (Score) Chamber height (cm) Chamber base insertion (cm / hr) Deploy. Duration (min) # of air samples Air sample storage duration (days) Very poor PoorGood Very good (0)(1)(2)(3) ≤5 >5 - 10 >10 - 20 >20 < 5 5 - <8 8 - <12 ≥12 >60 >40 -60 >20 - 40 ≤20 123>3 Plastic syringe >2 1 - 2 ≤1 Glass syringe >4 >2 - 4 1 -2 ≤1 others>90 >45 - 90 > 15 - 45 ≤15

19. Minimum Standards for NFT-NSS Chambers Use insulated and vented “base-and-collar” chambersUse insulated and vented “base-and-collar” chambers Avoid chamber heights < 10 cmAvoid chamber heights < 10 cm Insert to ≥ 5 cmInsert to ≥ 5 cm Use pressurized fixed-volume containers of known efficiency for air sample storageUse pressurized fixed-volume containers of known efficiency for air sample storage Include a minimum of three discrete air samples during deployment; including one at time=0Include a minimum of three discrete air samples during deployment; including one at time=0 Test non-linearity of changes in headspace concentration with time for estimating dC/dt at time=0Test non-linearity of changes in headspace concentration with time for estimating dC/dt at time=0

21. Measurement of Soil N 2 O Emissions > 600 reports in literature since 1980> 600 reports in literature since 1980 MethodologyMethodology –Steady-state chambers (open) –Non steady-state chambers (closed) –Soil profile –Micrometeorological methods > 98% measured using non flow-through non steady- state chambers (NFT-NSS)> 98% measured using non flow-through non steady- state chambers (NFT-NSS) National GHG inventories (IPCC) and model calibration are based on chamber measurementsNational GHG inventories (IPCC) and model calibration are based on chamber measurements

22. Number of Characteristics Reported Proportion of studies (%) <4 4 to 7 8 to 11 12 to 15 36% of the studies reported < half of the characteristics

23. Binary Characteristics Characteristic Proportion of studies reporting the use of each characteristic (%) Chamber type 91 Time zero sample 66 Insulation49 Vent47 Press. air samples 35 T corrections 33 QC air sample 17 Non linear dC/dt 15 “zero slope“ tested 5 Only 4 characteristics are reported in >50% of the studies

24. Numerical Characteristics Proportion of studies (%) About 1 out of 2 studies uses poor chamber insertion depth, air sample handling and chamber deployment duration

25. Proportion of studies (%)Factors Good chamber design Poorly used …

26. NFT-NSS Chamber Methodology Confidence Level (% error) High (<10%)High (<10%) No poor or very poor factorsNo poor or very poor factors Medium (<30%)Medium (<30%) ≤2 poor and no very poor factors≤2 poor and no very poor factors Low (10 – 50%)Low (10 – 50%) ≥3 poor factors≥3 poor factors 1 poor and 1 very poor factors1 poor and 1 very poor factors Very Low (20 – 60%)Very Low (20 – 60%) ≥2 poor factors and 1 very poor factors≥2 poor factors and 1 very poor factors >2 very poor factors>2 very poor factors

27. Level of Confidence in NFT-NSS measurements Proportion of studies (%) Time Intervals Confidence is low in the N 2 O flux reported by 60% of studies

28. Conclusions Confidence in soil N 2 O fluxes was estimated as low or very low in 60% of the 362 studiesConfidence in soil N 2 O fluxes was estimated as low or very 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 rigorous methodologyGreater effort is required to adopt and report more rigorous methodology Greater vigilance by reviewers and editorsGreater vigilance by reviewers and editors