Monitoring Greenhouse Fluxes and Soil Thermal Properties in a Central Missouri Soybean Field Over 5 Years – 2004-2008.

Greenhouse gases (CO₂, CH₄ and N₂O) emissions were monitored in a soybean field at Lincoln University's Freeman farm from 2004 to 2008. Static and vented chambers of 0.30 m long and 0.20 m diameter were installed at the beginning of each growing season in corn field. The chamber top had a middle hole covered by a stopper and used for air vacuuming and sampling. Soil air samples for determinations of CO₂, CH₄ and N₂O were collected at least twice a month from May to December. The sampling process consisted in closing the chamber two ventilation holes with rubber stoppers, collecting an air sample with a 50 ml syringe and storing it in a 200 ml Tedlar bag. Analysis of CO₂, CH₄ and N₂O from air samples was done within two hours with a Shimadzu GC-14. Soil samples were collected for analysis of chemical and physical properties. Soil temperature (T), thermal conductivity (K), resistivity (R), diffusivity (D) and volumetric heat capacity (C) were directly measured with KD₂ probe. A year to year analysis of data showed that the soybean field was a source for CO₂ and N₂O from 2004 to 2008 as follows: for CO₂: 2004<2005>2006<2007>2008 and for N₂O: 2004<2005>2006<2007<2008. The soybean field was a sink (2004 >2005) but also a source (2006 >2007<2008) for CH₄. Gases fluxes correlated among themselves mainly in 2005. N₂O was only correlated with T and only in 2005, 2007 and 2008.  CO₂ had more correlations with thermal properties in 2007 and 2008. Correlation coefficients ranged from 0.20 to 0.80. Although the discrepancies in the relationships between gases fluxes and soil thermal properties still show the need for continued research, this study provides useful information that can be used in predictive models of greenhouse gases emissions.