1. Second-generation biofuel feedstocks and the carbon economy of US agriculture
Ilsa Kantola
University of Illinois at Urbana-Champaign
DeLucia – Khanna – Long – Parton – David – Voigt – Hudiburg
Anderson-Teixeira – Dwivedi – Jaiswal – Wang – Hartman

2. Applications for carbon measurements
Miscanthus (Mg ha-1 yr-1)
Switchgrass (Mg ha-1 yr-1)
Our work combines on-the-ground research with modeling of yields, GHG effects, and economic cost-benefit analyses of bioenergy crops, though the use of the DayCent models that I showed you last year. I’m one of the ecologist/soil scientists, so I’m going to share some of the carbon research we do to support our models and projections.

3. Predicted yields N App. (kg/ha/yr): 0 P & K: Replacement
Adams, IN: 180
Marion, IL: 228  Talladega, AL: 100
P & K: Replacement
N App. (kg/ha/yr):
Adams, IN: 100
Marion, IL: 120  Talladega, AL: 100
P & K: Replacement
Our predictions of perennial yield began with by producing and then checking DayCent’s ability to model yields in corn, and when we were ahppy with those we moved on to Switchgrass and Miscanthus. We initially predicted yields in Illinois to be between 15 and 20 Mg/ha, for switchgrass, and between 25 and 27 for miscanthus. Yield is expected to vary with soil type, moisture regime, climate, and management.

4. Predicted carbon accumulation
Along with biomass yield predictions, we are able to predict increases in soil organic carbon under perennial crops, and losses of soil carbon under corn. These predictions show that both switchgrass and miscanthus are expected to increase soil C by approximately 1 Mg/ha/yr, so in ten years of biomass growth, we’re looking at 10 Mg C sequestration per hectare for switchgrass and approximately twice that for miscanthus.

5. Yield Trials (2002-2012) M. x giganteus P. virgatum Location DeKalb
M. x giganteus
P. virgatum
Location
Estimate SE
DeKalb
16.34
2.87
7.45
1.14
Havana
16.58
2.86
9.92
1.21
Urbana
31.14
2.57
13.71
1.08
Orr
25.35
10.38
Brownstown
14.70
8.51
Fairfield
30.24
11.07
Dixon Springs
30.02
9.42
Average
23.4
1.20
10.0
0.90
However, yield trials and long-term studies around the state of Illinois have shown us that yields are highly variable in Illinois alone, and only a few places are achieving the numbers predicted by the DayCent models.
Arundale, Dohleman, Heaton, McGrath, Voigt & Long (2014) GCB-Bioenergy 6, 1-13.

6. Observed carbon changes, Illinois
We share a group of sites with Becky Arundale and Emily Heaton, in addition to the Energy Farm sites at the University of Illinois. The statewide sites are slightly older, and on a variety of soils, to capture soil and climate effects on energy crop growth. And what we’ve seen in the soil carbon, as with the plant biomass, is a lot of variability in the accumulation of carbon on these sites. At many of them carbon is increasing, but not at the rates we expect, or in the way predicted by our models.

7. UIUC Energy Farm
Our most intense research has been carried out at the University of Illinois Energy Farm. WE have been sampling these soils continuously since 2008, and measuring a number of factors.

8. Observed carbon changes, UIUC Energy Farm
0-10 cm
10-30 cm
At the farm we fall into the conundrum of soil carbon set up by our models: Daycent tells us the carbon yield should be 5 tons by 2013, but we’re seeing a 50% increase, with a lot of variability. And less response in deeper soils, making it hard at this stage to declare soil C to be increasing.

9. Indicators of carbon cycle perturbations
Carbon source change
Soil structural change
POM and C isotopes
So while soil carbon concentration is the number we’ve modeled, and the number we focus on, there are other characteristics of soil and soil carbon that contribute to the soil carbon stocks and their residence times.

10. Carbon sources Perennial BG biomass exceeds corn and soy by 550-750%
As you are aware, annual and perennial crops are handed differently. Perennials don’t require tillage and planting every year, generally require less fertilization, and less herbicide and insecticide application. In the case of perennial grasses, the biomass is harvested much later in the season than corn or soy, to allow for nutrient retranslocation to the soil during senescence. As for inputs to the soil, we compare corn with miscanthus and switchgrass, and what we find is that the belowground biomass of the perennial crops exceeds corn and soy by percent. Now, we can consider annual roots to turnover every year, as they die at the end of the growing season, while only a portion of the perennial roots turnover every year. If only 20% of perennial roots turns over every year, a conservative estimate for grasses, perennial belowground inputs are still double those of annuals. Conversely, litter inputs from corn and soy average 200 to 250% of perennials. We have included both above- and belowground material in a decomposition study that placed the carbon source material either at the soil surface or belowground, and then measured rates of decomposition. What we found was that buried corn material, roots and litter, which gets buried when cornfields are tilled, decomposes faster than perennial material. So we’re seeing a change both in the magnitude of the inputs from these two sources, and how long they linger in the soil.
Corn/soy litter averages 200% of miscanthus and 250% of switchgrass

11. Soil structural changes
53 μm
250 μm
2 mm
University of New England
1 mm
250 μm
53 μm

12. C4 signal in POM increases with time
C4 carbon
Original soil

13. The mystery remains Undecomposed litter
Microbially-processed plant material
The unseen processes of soil carbon accumulation remain our focus, we’re working on methods to differentiate the different soil carbon pools from each other. We can do some of it with isotopes, but we’re also looking at spectroscopic and chemical techniques for isolating carbon based on its source and it’s intermediate states.
Plant exudates

14. Conclusions The soil C landscape is changing with perennial crops
Soil C is accumulation slower and more variable than expected under perennial crops
The mechanisms of C accumulation differ between corn and perennial crops
Significant amounts of C4 carbon are being added to and retained in the soil by biofuel crops
Models will adjust with the research as long-term data becomes available
The soil carbon landscape, the behavior and characteristics of the soil carbon, is changing with perennial crops. The mechanisms of carbon accumulation differ as well: a shift in input sources and decomposition characteristics. Soil carbon accumulation is slower and more variable around the state of Illinois than we initially projected with our models, but significant amounts of C4 carbon are being added to and retained in the soil by biofuel crops. All of our field word cycles back into our models, allowing us to refine them with long-term data.

15. Contributors
Evan DeLucia Mark David Madhu Khanna Steve Long Bill Parton Tom Voigt Krista Anderson-Teixeira Puneet Dwivedi Melanie Hartman Tara Hudiburg Deepak Jaiswal Weiwei Wang ..and our statewide partners