Sustainable Bioenergy Crop Production Research Facility

R. Michael Miller, Argonne contact (rmmiller@anl.gov)

In June 2008, we planted a field research facility designed to identify plant and microbial processes that can optimize sustainable low-input (fertilizer) bioenergy feedstock production and, at the same time, enhance carbon sequestration into longer-turnover soil organic matter pools.  The 5.4-ha facility is located at the Fermilab National Environmental Research Park in Batavia, IL.

In the primary experimental area, seven vegetative treatments contrast three switchgrass ecotypes originating from different latitudes with four mixtures of increasing complexity:

KA     Kanlow switchgrass (lowland cultivar originating from central Oklahoma),

CR    Cave-in-Rock switchgrass (upland cultivar originating from southern Illinois),

SL     Southlow Michigan Germplasm switchgrass (upland germplasm originating from the southern lower peninsula of Michigan),

SG    A mixture of the three switchgrass ecotypes (to increase genetic diversity while maintaining a pure switchgrass feedstock),

CW   A mixture of the three switchgrass ecotypes with a single ecotype of Canadian wild rye (a rapid-growing native prairie grass that is expected to speed switchgrass establishment by reducing weed competition),

BB    A mixture of the three switchgrass ecotypes with three big bluestem ecotypes (big bluestem is another native prairie grass that is more nutrient-use efficient than switchgrass),

PR    A mixture of four native prairie grasses (switchgrass, big bluestem, Canadian wild rye, and Indiangrass) with eight native prairie forbs.

In addition, two nitrogen fertilization treatments (0, and 60 lb N/acre) are superimposed over the vegetative treatments beginning in the 2009 growing season.  All treatments are replicated three times giving a total of 42 plots separated by alleys planted with short-stature bunchgrasses.  The large plots (36 m x 20 m) can accommodate repeated sampling.  In addition, an eddy flux tower located within the experimental area continuously monitors CO2, water, and energy fluxes at the site, which enables us to determine the net ecosystem production and carbon sink strength of the facility.

The plots were established on soils that supported a stand of Eurasian pasture grasses for 36 years, which allows use of the natural carbon isotope ratio technique to estimate the contribution and fate of new root-derived carbon to soil organic matter pools.  This technique is based on the differential discrimination of the heavier 13C isotope during assimilation by plants with different photosynthetic pathways.  The C3 photosynthetic pathway found in Eurasian pasture grasses leads to a 13C depletion of about ‑19‰ compared to air, which results in δ13C values of C3 plant tissues of about ‑27‰.  In contrast, switchgrass and most native prairie grasses use the C4 photosynthetic pathway, which results in a smaller depletion and a δ13C of about ‑13‰.  The 13C signature of soil organic matter reflects the δ13C of plant inputs.  Hence, growth of switchgrass and other C4 prairie grasses on soil that previously supported C3 grasses for an extended time enables estimation of the contribution of switchgrass carbon inputs to soil organic matter over time.

In addition to the primary experiment, replicated field trials of additional switchgrass and big bluestem ecotypes were established in 60 smaller plots (2 x 1 m) to examine how root traits (e.g., physiology, phenology, morphology, and longevity) and their potential effects on associated microbial communities affect sustainable biomass feedstock production and carbon sequestration.  Geoff Morris and Justin Borevitz of the University of Chicago also established 166 experimental miniplots (2 x 3 m) within the facility to investigate how the genetic diversity of switchgrass and big bluestem affects bioenergy feedstock production.  Lastly, the 0.5-ha area in the northwest corner of the facility was planted with seed harvested from Fermilab’s restored prairies to allow direct comparisons to soil carbon sequestration rates under local native prairie ecotypes.

Herbicided pasture grasses at facility edge, fall 2007	Controlled burn of pasture grass residues, fall 2007
Burned pasture grass residues, fall 2007	Facility edge, early spring 2008
Spring 2008 vegetative re-growth at facility edge	Overview of vegetative re-growth before spring 2008 herbicide application
Drill seeding primary experimental plots, June 2008	Drill seeding primary experimental plots, June 2008
Planting U of C genetic diversity miniplots, June 2008	Switchgrass seedlings 3 weeks after planting
Cave-in-Rock switchgrass 9 weeks after planting

Collaborators
Geoff Morris, University of Chicago, http://borevitzlab.uchicago.edu/Members/gmorris/homepage
Justin Borevitz, University of Chicago, http://pondside.uchicago.edu/ecol-evol/faculty/borevitz_j.html

Links
Fermilab prairie restorations:  http://www.fnal.gov/pub/about/campus/ecology/index.html
Argonne news release:  http://www.anl.gov/Media_Center/News/2008/BIO080718.html