313-16 Estimating Greenhouse Gas Fluxes by Gas Chromatography and the Photoacoustic Infrared Detection System.



Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Agnes Padre, Jagdish Ladha, Munmun Rai, Mahesh Gathala and Sheetal Sharma, IRRI-India, IRRI, New Delhi, India
Practical methodologies for estimating greenhouse gas (GHG) fluxes are needed in environmental studies to assess the impacts of agricultural practices on GHG emissions and C sequestration. The conventional static-chamber methodologies for measuring GHG, involve manual gas sampling, and analysis by gas chromatography (GC) while the photoacoustic infrared system (PAS), gives direct readings of GHG concentrations, eliminating the need for gas storage and analyses.

The CO2, N2O and CH4 fluxes from wheat fields in India were measured from static chambers in 32 plots(P) with 4 nitrogen(N) and 2 residue(S) treatments, on 23 sampling dates(D), by 2 methods(M): 1) manually taking 4 periodic gas samples at 10 min intervals and analyzing the gas concentrations by GC and 2) automatically recording 10 GHG concentrations at 1.2 min intervals using the PAS.

The 95% confidence limits of the slopes(emission rates) analyzed by regression analyses showed that GC and PAS estimates of CO2 and N2O fluxes within each plot, varied significantly (P<0.05) from each other in only 6-7%, of the 736 PxD measurements.

The SAS mixed procedure with repeated/group effect showed that for both N2O and CO2 fluxes, MxSxN interactions were not significant, but MxN and MxS were, for N2O and CO2 respectively. These results indicate that the 2 methods exhibited similar trends for SxN but not for S and N means. GC values were generally higher for N2O but lower for CO2 than those of the PAS. However, GC data also showed greater variability than those of the PAS such that no significant differences were found between GC and PAS estimates for N2O and CO2 in all except 1 of the 8 SxN treatments averaged over 4 reps and 23D.

Both methods showed no significant CH4 emission on all sampling dates after the PAS-CH4 concentrations were corrected for changes in water vapor over time.

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Management Impact On GHG Emissions and Soil C Sequestration: III