Zenone T, Chen J, Wilske B, Deal M, Hamilton S, Jasrotia P, Kahmark K, Bohm S, Robertson G.P.
Presented at the GLBRC Sustainability Retreat (2010-02-10 to 2010-02-12 )
Land use changes, primarily expansion of annual cropping systems into forests and grasslands, are deemed responsible for 20–25% of the increase in atmospheric CO2 that has occurred over the past 150 years. In this study we examined the winter CO2 fluxes, using eddy covariance (EC) technique, across seven agricultural sites in Midwest US. The experimental sites are located in southern Michigan in the northeast portion of the U.S. Corn Belt at the MSU W.K. Kellogg Biological station (KBS). Among the 7 study sites, three fields had been continuous corns while other four managed as conservation prairies in the past 20 years. In order to study the effect on land use change during May 2009 six field (three managed as conservation prairie and three previous cultivate with corn) has been converted in soybean cultivation while one site has been left manage prairie as reference. In early May, herbicide (Glyphosate- Roundup) was applied to kill the vegetation prior to plantations of soybeans to homogenize the fields for developing the three biofuel systems in 2010. The preliminary results obtained from the EC tower measure from December 2008 to July 2009 show the temporal trend of CO2 flux across the sites: the corn fields were substantially carbon neutral during winter while the prairies were carbon source with an average value of 15 g C m-2 mouths-1 emitted from December to march. In April, while fields corn still continued to be a source of CO2, prairie switch from source to sink of C. In early may, about 2 days after herbicide application, the prairie sites switch from sink to source due to the effect of herbicide. After sowing (middle of June) all sites continued to show an emission of C until the end of the month. In July, due to photosynthetic activity of soybean cultivation, the sites previous cultivated with corn have become C sink with values ranging from 15 to 50 g C m-2 month-1 gain. On the other hand the strong ecosystem respiration due to the conversion from prairie to soybean has kept those sites carbon source. The temporal trend of CO2 absorption/emission at the reference site showed a typical trend of an unmanaged ecosystem with a low emission of C during winter and sequestration in spring and summer due to the photosynthetic activity.
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