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Comparison between a Photo-Acoustic Analyzer System (PAS) and Gas Chromatograph (GC) for Measuring CO2 and N2O Emissions in a Corn/Soybean Field

There is a need to compare greenhouse gases (GHGs) measurements methods for data harmonization. The objective of this study was to compare Gas Chromatography (GC) and a Photo-Acoustic Analyzer System (PAS) as methods for measuring carbon dioxide (CO2) and nitrous oxide (N2O) emissions in a corn/soybean field. The study was conducted on a Waldron silt loam soil at Freeman farm of Lincoln University of Missouri. Sixteen cylindrical polyvinylchloride static chambers measuring 0.30 m in height and 0.20 m in diameter were permanently inserted into the soil to a depth of 0.05 m for GHGs measurements. Soil air samples were collected in each chamber with a 60 ml syringe and stored in a Tedlar bag for CO2 and N2O analysis by GC within 2 hours of sampling. CO2 and N2O measurements with PAS were done directly in-situ. Significant, stronger and positive correlations were found between PAS and GC in 11 out of 15 months - measurement cycles for CO2. The most significant correlation was observed in April 2015 (r = 0.90, p = 0.0001). For N2O, however, only 5 out of 15 measurements between PAS and GC had positive, but weak correlations. The highest correlation between PAS and GC measurements for N2O was also found in April 2015 (r = 0.71, p = 0.0020). Continuous monitoring of GHGs emissions is necessary to better understand their dynamics and how they are exacerbated by agricultural management practices. However, accurate measurement techniques are also needed.