Presentation at NSERC Strategic Project Presentation at NSERC Strategic Project Meeting – GuelphMeeting – Guelph

Jan 10, 2008Jan 10, 2008Claudia Wagner-RiddleClaudia Wagner-Riddle

• Previous experience with isotopic CO2 measurements of soil respiration

• Proposed research for 2008, 2009

Previous Project: Temporal Dynamics of Greenhouse Gas Fluxes linked to Soil Biophysical

Processes and Management Practices

• Co-applicants: U. of Guelph, U. of Manitoba, AAFC • Duration: Sep 30, 2004 to Sep 29, 2007• Funds for purchasing tunable diode laser trace gas

analyzer for 13CO2 and 12CO2 concentration measurements

• One of objectives:

– to determine fraction of soil CO2 flux originating from soil organic carbon or crop residue carbon for no-tillage (NT) vs. conventional tillage (CT) over time

Research Site: Elora (Ontario)

• Four 1.5 ha plots: conventional practices (2 plots); "best management" practices (2 plots) since 2000; since May 2005 treatments these were NT and CT

• Corn/soybean/winter-wheat/corn/soybean over 2000 to 2004; corn in 2005

2 (NT)2 (NT)

3 (NT)3 (NT)

1 (CT)1 (CT)

4 (CT)4 (CT)

Trailer

Four 1.5-ha Plots (Ontario)Four 1.5-ha Plots (Ontario)

Field: -air intakes (up/down x 4 plots)

Trailer: -sampling manifold-tanks-dryer-TGA-pumps

Stable Isotope Studies at EloraStable Isotope Studies at Elora

30 s tank A

30 s tank B

15 s each height for 4 min

Switching cycle for one plot over 30 minSwitching cycle for one plot over 30 min

Weekly calibration (working vs. transfer or ’golden’ tanks)Weekly calibration (working vs. transfer or ’golden’ tanks)

Measured by TGA(diff. in conc. between 2 heights)

Flux Ratio Calculation of 13CR (Griffis et al., 2004)

Note: Applicable to soil respiration only when vegetation is not present

CO2 Fluxes

Fall 2005

CT × NT +

Flux Ratio calculation of 13CR

Fall NT ~3.5‰ lower than CT plot Fall to Spring Change ~-4‰

Keeling Plots

Footprint for concentration measurement larger than 1.5-ha plots so that difference between treatments can not be detected

Findings• The respired soil CO2 signature showed a stronger C4

signature compared to the no-till field where crop residue was left on the soil surface during fall and spring

• This means a larger proportion of measured soil CO2 flux in fall originated from crop residue in CT compared to NT (76.2 vs. 61.5% in fall; 60% vs. 45.1% in spring)

• These results suggest that NT will increase C storage, contradicting previous studies in eastern Canada

• It may be that decomposition under NT increases at some time subsequent to the measurement periods reported here (i.e. summer, when vegetation is present)

New Research Question

• How to derive 13CR from in-canopy 13CO2 and 12CO2 concentration measurements?

13CO2 and 12CO2 concentrations measurements

Proposed MeaurementsProposed Meaurements

• Canopy measurements

Laser and Dewar

PC

Electronics Absorption tubeReference cell and detector

Sample cell and detector

Edwards et al. (2002)

• TGA100 adapted to measure mole fractions of 12CO2 and 13CO2 by Bowling et al. (2003) – Based on mostly same hardware– Software change to allow for simultaneous scanning of two

absorption lines (one for each isotopomer)– Analyzer optimized for accuracy and precision

• TGA100 tested in 26-day field experiment in Minnesota (after soybean harvest) by Griffis et al. (2004)

• Characteristics:– 10 Hz noise of 13C 0.5‰, calibrated noise <0.15‰ 13CR can be obtained by ratio of fluxes (F13CO2/F 12CO2) instead

of Keeling plot

Stable Isotope Studies using TDLASStable Isotope Studies using TDLAS