Comparison of the Carbon Budget, Evapotranspiration, and Albedo Effect between the Biofuel Crops Switchgrass and Corn

Abstract:

Switching from annual cropping systems to perennial crops like switchgrass (Panicum virgatum L.) for biofuel feedstock production will have implications on carbon and water cycling as well as biophysical parameters, such as surface albedo.
We conducted eddy covariance measurements of carbon dioxide and water fluxes over a mature (>5 years) switchgrass field over three years (2012 to 2014) and a continuous corn field during the year 2014. Both fields were located in Southern Ontario, Canada. Results for carbon and water cycling were compared between the two crops for the year 2014. Differences in surface albedo between the two biofuel cropping systems were compared for the years 2012, 2013, and 2014. In 2014 switchgrass was a carbon sink with a net ecosystem carbon balance (NECB) of −66±59 g C m^-2, while corn was a carbon source with an NECB of 328±30 g C m^-2 for a scenario where corn grain only is harvested and 634±34 g C m^-2 for a scenario where both grain and stover are harvested. Annual evapotranspiration in 2014 was higher for the corn field (608.7±12 mm) than for the switchgrass field (517.0±8 mm). Albedo measurements showed an average annual negative radiative forcing effect for the switchgrass field compared to corn. Differences in albedo were largest in spring and fall when radiative forcing values of −10.2 and −5.5 W m^-2 were observed, respectively.
Comparing carbon cycling results from previous years, the switchgrass field was a source of carbon in 2012 (NEBC 106±45 g C m^-2), but a small sink of carbon in 2013 (NEBC −59±45) and 2014. On average over the three measurement years, the switchgrass field was carbon neutral.
Qualitative analysis of the carbon budget, evapotranspiration, and albedo results from this study suggest that biofuel produced from switchgrass can have more climate benefits than biofuel from continuous corn. This study provides important data for improvement of Life Cycle Analysis of switchgrass biofuel.