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Philippe Rochette, AAFC Québec City

Philippe Rochette, AAFC Québec City. Research on gaseous emissions from agricultural soils at the Québec City AAFC research centre. CO 2. Plant roots. Soil org. C. Soil inorg. C. old. carbonates. recent. Soil respiration is the sum of several CO 2 sources. Soil respiration.

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Philippe Rochette, AAFC Québec City

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

  2. CO2 Plant roots Soil org. C Soil inorg. C old carbonates recent • Soil respiration is the sum of several CO2 sources Soil respiration

  3. Natural Abundance of 13C • About 1.1‰ of atmospheric CO2 is 13CO2 (-8‰) • Greater discrimination against 13CO2 by Rubisco than by PEP carboxylase • More 13C in C4 (-12‰) than in C3 plants (-26‰)

  4. 13CO2 = -26‰ -12‰ > 13CO2 > -26‰ CO2 CO2 C3Soil org. C -12‰ -26‰ CO2 C3 Soil org. C -26‰ Rhisophere RespirationRochette and Flanagan,1997; Agron. J.Rochette, Flanagan and Gregorich,1999; Agron. J. Rrh = Rtot x Rrh,frac. 1 > Rrh,frac. > 0 C4 plant

  5. Contribution of corn-C to soil CO2 40 0>Rrh,frac<1 35 30 25 20 15 RHIZOSPHERE / TOTAL RESPIRATION (%) 10 cm 10 20 cm 5 40 cm 0 -5 -10 140 160 180 200 220 240 260 280 300 320 DAY OF YEAR

  6. Separation of soil respiration into corn and native C sources Rt Rs Rrh

  7. Oxydation de la matière organiqueQ10 = 2

  8. 13CO2 = -26‰ -12‰ > 13CO2 > -26‰ C4 residue CO2 -12‰ C3Soil org. C -26‰ CO2 CO2 C3 Soil org. C -26‰ Maize residue decompositionRochette, Angers and Flanagan,1999; Soil Sci. Soc Am. J. C3 plant Rres = Rtot x Rres,frac. 1 > Rres,frac. > 0

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

  10. Decomposition rates of maize residues Rres=Rt x Rres,frac

  11. Chamber measurements of soil N2O emissions: Are they reliable? Rochette and Eriksen-Hamel (2008)

  12. Objectives • Determine criteria for assessing the quality of soil N2O flux measurements made using NFT-NSS chambers • Apply 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 N2O flux

  13. Definition of Criteria • Criteria to evaluate NFT-NSS chamber methodology were determined based on: • Hutchinson and Livingston, 1993 • Livingston and Hutchinson, 1995 • Holland et al., 1999 • Hutchinson and Livingston, 2002 • Davidson et al., 2002 • Smith and Conen, 2004 • Rochette and Hutchinson, 2005 • Rochette and Bertrand, 2007

  14. Dataset • Chamber methodology was evaluated on a sample of the 362 studies reporting soil N2O emissions measured using NFT-NSS chambers. Selected studies were from: • Stehfest and Bouwman, 2006 • Jungkunst et al., 2006 • Lu et al., 2006 • Survey of recent literature

  15. NFT-NSS chamber design and methodology N2O concentration NL/L: 0.48/0.35 = 1.4 FN2O = dC/dt • V/A • Mm/Mv• (1-e/P)

  16. Characteristics for evaluating NFT-NSS chamber methodology • Characteristics are simple descriptive criteria grouped in two types: • Binary ("yes or no“ type) • Numerical (“quantitative” (cm, cm2, cm3, min, …) )

  17. NFT-NSS Chamber Scoring of Binary Characteristics

  18. NFT-NSS ChamberScoring of Numerical Characteristics

  19. Minimum Standards for NFT-NSS Chambers • Use insulated and vented “base-and-collar” chambers • Avoid chamber heights < 10 cm • Insert to ≥ 5 cm • Use 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=0 • Test non-linearity of changes in headspace concentration with time for estimating dC/dt at time=0

  20. Measurement of Soil N2O Emissions • > 600 reports in literature since 1980 • Methodology • 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) • National GHG inventories (IPCC) and model calibration are based on chamber measurements

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

  22. Binary Characteristics Only 4 characteristics are reported in >50% of the studies

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

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

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

  26. Level of Confidence in NFT-NSS measurements Confidence is low in the N2O flux reported by 60% of studies Proportion of studies (%) Time Intervals

  27. Conclusions • Confidence in soil N2O fluxes was estimated as low or very low in 60% of the 362 studies • This proportion was 50% in recent studies (2005-07) • Causes for poor scores: • incomplete description of methodology • plastic syringes • shallow insertion • low number of air samples • Greater effort is required to adopt and report more rigorous methodology • Greater vigilance by reviewers and editors

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