A variety of techniques are available for measurement of soil CO2 flux in the field, and each method has inherent advantages and disadvantages. On 5 dates in October, 2005 we measured soil CO2 emissions in a central Iowa soybean field using: i) eddy covariance, ii) a commercially available soil chamber, iii) an automated soil chamber system, and iv) a soil gradient technique. Fluxes from the two chamber methods were not significantly different. Eddy covariance estimates were different from the chamber fluxes on two dates. The diffusion method consistently yielded lower CO2 emission estimates than the other methods. It is thought that inaccuracies in determining the soil CO2 diffusion coefficient may be responsible for these observations.