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MEMORANDUM

TO: Air and Radiation Docket EPA-HQ-OAR-2014-0537

FROM: EPA Office of Transportation and Air Quality

DATE: December 17, 2014

SUBJECT: Agricultural Inputs and Cellulosic Content of Biomass Sorghum

This memorandum provides information on sources of data used for EPA’s analysis of the 

greenhouse gas emissions associated with the cultivation of biomass sorghum. It also provides 

information on the data used to calculate the adjusted cellulosic content of biomass sorghum. 

A. AGRICULTURAL INPUTS AND EMISSIONS

To determine the greenhouse gas emissions associated with growing biomass sorghum, EPA 

used data from the petition, literature, and USDA. The data and sources are summarized here, 

and details of how the data were used to calculate greenhouse gas emissions are provided in a 

spreadsheet available on the docket.a 

1. Yield

To estimate an average yield in 2022, we started with an assumed biomass sorghum yield of 11 

dry tons/acre in 2012. This value is based on an average of data from several sources, which

showed results of field trials in Indiana, Texas, Kentucky, Mississippi, North Carolina, Kansas, 

Iowa, Michigan, and Illinois.

1,2,3,4,5,6,7,8

 Trials took place between 1979 and 2010, and used a 

range of growing conditions. The average yield based on all of these studies was 10.77 dry

tons/acre, with a range of 5.84 to 26.32 dry tons/acre. Values in the higher end of this range 

came from a single study.5 If this study is excluded, the range in yield is 5.84-15.66 dry

tons/acre. 

 

a

See “Biomass sorghum data – for docket.xlsx” placed in docket EPA-HQ-OAR-2014-0537.
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We assumed that the yield for biomass sorghum would increase by 2% per year, based on similar 

yield improvements that were projected for switchgrass. Based on this yield improvement, we 

calculated a biomass sorghum yield of 13 dry tons/acre in 2022. This value was used for 

subsequent emissions calculations.

2. Fertilizers

We used fertilizer input values of 60 lbs nitrogen/acre, 15 lbs phosphorus/acre, and 7 lbs

potassium/acre. These values are based on data provided by the petitioner, which cited Forest 

and Agricultural Sector Optimization Model (FASOM) documentation as a source.b Using a 

yield of 13 dry tons/acre, the fertilizer inputs per dry ton are: 4.6 lbs nitrogen/dry ton, 1.2 lbs

phosphorus/dry ton, and 0.5 lbs potassium/dry ton. 

3. Other inputs

The petition provided two diesel input values: 9.2 gal/acre, based on FASOM documentation, 

and 7.35 gal/acre based on GREET 2011 and two reports.

9,10

 We used the more conservative 

value of 9.2 gal/acre, which is 0.7 gal/dry ton feedstock. For herbicide inputs, we used USDA’s 

estimate for energy cane, which is 5.5 lbs/acre, or 0.4 lbs/dry ton feedstock.

c

 For pesticides, the 

petition provided the greenhouse gas emissions based on FASOM data, rather than the quantity 

of pesticide used. We used this value (0.0006 tons CO2e/acre) to calculate the quantity of 

pesticide used, based on our emission factor for pesticides. This calculation resulted in a 

pesticide input of 0.044 lbs/acre, or 0.003 lbs/dry ton feedstock. 

4. N2O emissions

 

b

For more information about FASOM, see Beach, R.H. and B.A. McCarl (2010). “U.S. Agricultural and Forestry 

Impacts of the Energy Independence and Security Act: FASOM Results and Model Description.” RTI International,

and Beach, R.H. et al. (2010). “Model documentation for the Forest and Agricultural Sector Optimization Model 

with Greenhouse Gases (FASOMGHG).” RTI International.

c The petitioner did not estimate herbicide use in their petition. As a conservative estimate, we used the value of

herbicide use for energy cane, as provided by the USDA. Information on the energy cane analysis is available on 

docket EPA-HQ-OAR-2011-0542.
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N2O is emitted from synthetic nitrogen fertilizer, as well as from the decay of crop residues. The 

Intergovernmental Panel on Climate Change (IPCC) provides equations for direct emissions 

from these sources, and indirect emissions from the volatilization of synthetic fertilizer, and 

leaching/runoff of all nitrogen sources.11 The IPCC also provides emission factors for these N2O 

sources.

To calculate the amount of crop residues, we used equations and factors in the IPCC. With these 

equations, the crop yield is used to calculate the amount of above-ground residue, and the ratio of 

below-ground residue to above-ground biomass (including harvested material) is used to 

calculate the amount of below-ground residue. The IPCC provides a table of factors to calculate 

crops residues and the nitrogen content of crop residues for a variety of crops.d Because factors 

for biomass sorghum are not included in this table, we used the factors provided for “Perennial 

grasses.” We chose this value because the harvesting of biomass sorghum is likely to be similar 

to the harvesting of perennial grasses – most of the plant will be harvested, with little residue 

remaining, in contrast to crops like corn or grain sorghum where only the grain is harvested. 

However, because perennial grasses have a more developed root system than annual crops, it is 

likely that our calculations overestimated the below-ground biomass, and therefore 

overestimated the N2O emissions from below-ground biomass. We calculated an above-ground 

residue of 3.9 tons/acre and a below-ground residue of 13.5 tons/acre for a yield of 13 dry

tons/acre. Total direct and indirect N2O emissions from nitrogen fertilizer and crop residues are

105 kgCO2e/dry ton. Further details of these calculations can be found in the associated 

spreadsheet on the docket.e 

5. Total emissions from chemical and energy inputs and crop residues

We used the emission factors documented in the March 2010 rule to calculate the emissions from 

fertilizers, herbicides, pesticides, and diesel.

f

 These results are shown in the spreadsheet posted 

 

d Table 11.2 in 2006 IPCC Guidelines for National Greenhouse Gas Inventories.

e

See “Biomass sorghum data – for docket.xlsx” placed in docket EPA-HQ-OAR-2014-0537.

f

75 FR 14670 and associated material in Docket EPA-HQ-OAR-2005-0161.
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on the docket.g Total emissions from agricultural inputs and crop residues (including N2O 

emissions) are 128 kgCO2e/dry ton feedstock.

B. CELLULOSIC CONTENT

For biomass sorghum-derived biofuels to qualify as cellulosic biofuel under the RFS program, 

the fuel must achieve a 60% lifecycle GHG reduction as compared to the 2005 baseline fuels, 

and must also be derived from cellulose, hemicellulose and lignin.

h

 In the rule published on July

18, 2014 (the “July 2014 rule”),

i

EPA determined that fuel generated from feedstocks with an 

average adjusted cellulosic contentjof 75% or more is eligible to generate cellulosic biofuel 

RINs for the entire fuel volume. In that rulemaking, EPA also explained that we would apply the 

75% threshold to feedstocks that we evaluated in the future, and finalized a definition of energy

cane, which can have a wide range of cellulosic contents. Consistent with that rulemaking, we 

have evaluated the cellulosic content of biomass sorghum, based on two scientific studies and 

industry data. Data and calculations can be found in the spreadsheet posted to the docket.k 

One study presented compositional data for 22 varieties of forage sorghum.12 The composition 

was measured using National Renewable Energy Laboratory (NREL) Laboratory Analytical 

Procedures.13 The samples included photoperiod sensitive (PS) varietieslas well as non-PS 

varieties. Data in the paper showed that the PS varieties had higher yields than the other 

varieties, and that these higher yields were similar to the yields of other bioenergy crops. For our 

calculations, we separated the varieties into “high-yield” (the PS varieties), 

“sorghum/sudangrass” (which includes two of the PS varieties), and “forage.” Although the 

paper did not specifically categorize any of the samples as biomass sorghum, we assumed that 

 

g

See “Biomass sorghum data – for docket.xlsx” placed in docket EPA-HQ-OAR-2014-0537.

h

For simplicity, these three chemicals are hereafter referred to as “cellulose,” and their presence in feedstock as the 

feedstock’s “cellulosic content.” 

i

“Regulation of Fuels and Fuel Additives: RFS Pathways II, and Technical Amendments to the RFS Standards and 

E15 Misfueling Mitigation Requirements.” 79 FR 42128

j Adjusted cellulosic content is the percent of organic material that is cellulose, hemicellulose, and lignin.

k

See “Biomass sorghum data – for docket.xlsx” placed in docket EPA-HQ-OAR-2014-0537.

l

Photoperiod sensitive sorghums flower when the length of the day is below a certain threshold (12 hours and 20 

minutes). This is in contrast to non-photoperiod sensitive varieties that flower when a certain amount of time has 

passed. Photoperiod sensitive sorghums can have a longer growing season, which means more biomass will be 

produced. See, e.g. Pennington, D. 2011. Photoperiod sensitive sorghum for bioenergy. Michigan State University 

Extension. Available at: http://msue.anr.msu.edu/news/photoperiod_sensitive_sorghum_for_bioenergy. Accessed 

December 12, 2014.
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the high-yield, photoperiod sensitive varieties are most similar to biomass sorghum, based on 

information from the petitioners.

This paper showed data for ash, protein, soluble sucrose, soluble starch, total solubles, lignin, 

glucan, xylan, galactan, arabinan, and total structurals. In addition, we received supplementary

data from the authors for water extractives, ethanol extractives, and acetyl.

m

 These data 

(published and supplementary) are included in the spreadsheet on the docket.n Using methods 

detailed in a separate memorandum,o we calculated the adjusted cellulosic content of the samples

(Table 1). We found that “high-yield” varieties had an average adjusted cellulosic content of 

75.4% (with a range of 68.9-82.8%), sorghum/sudangrass had an average adjusted cellulosic 

content of 70.0% (with a range of 61.2-75.8%), and forage sorghum had an average adjusted 

cellulosic content of 60.5% (with a range of 50.5-84.4%).

Another study presented data from 152 sorghum samples.14 51 of these samples were 

categorized as “biomass sorghum.” These samples were “photoperiod sensitive and produce[d]

little to no grain.” This study also presented data from 41 forage sorghum samples, 54 sweet 

sorghum samples, and 6 sorghum/sudangrass samples. The composition of the samples was 

analyzed using NREL Laboratory Analytical Procedures. This paper presented data on ash, 

protein, sucrose, lignin, xylans, glucans, and starch. Using these data, we found that the biomass 

sorghum samples had an average adjusted cellulosic content of 63.2%, the forage sorghum 

samples had an adjusted cellulosic content of 70.1%, the sweet sorghum samples had an adjusted 

cellulosic content of 61.8%, and the sorghum/sudangrass samples had an adjusted cellulosic 

content of 72.5% (Table 1).

We also received data from NexSteppe, a developer of sorghum hybrids that have been recently 

released or are under development, and for which there is not yet published data available. 

NexSteppe provided data from seven samples grown in four locations.15 NREL Laboratory

Analytical Procedures were used to measure the composition of the samples. NexSteppe 

provided data on the free sugar content, starch content, total cellulosic content, and adjusted 

 

m

See “Sorghum cellulosic content data from J. Dahlberg” placed in docket EPA-HQ-OAR-2014-0537.

n

See “Biomass sorghum data – for docket.xlsx” placed in docket EPA-HQ-OAR-2014-0537.

o

“Cellulosic Content of Various Feedstocks – 2014 Update” available in docket EPA-HQ-OAR-2012-0401.
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cellulosic content for each sample. The average adjusted cellulosic content was 83.7%, with a 

range of 77.4-88.6% (Table 1). 

Table 1—Chemical composition of different types of sorghum samples, as determined by 

two research studies and from industry data. The adjusted cellulosic composition was 

calculated by adjusting the reported content of cellulose, hemicellulose and lignin for the 

ash content and for the total yields.

Chemical Composition (%)

Source Dahlberg et al. (2011) Stefaniak et al. (2012) NexSteppe

Sorghum 

variety High-Yield

Sudan/ 

Sorghum Forage Biomass

Sudan/ 

Sorghum Forage Sweet Biomass

Number of samples 5 4 15 51 6 41 54 7

Sucrose 

(sugar)

Average 2.9 2.7 1.0 9.0 2.4 1.1 9.8 4.5

Range 1.6-4.6 0.4-3.5 0.2-1.7 0.3-19 0.4-4.6 0.2-3.0 0.2-23.9 1.2-8.5

Average 0.8 5.6 18.1 5.6 1.1 1.8 7.3 3.4

Starch Range 0-4 0-15 0-25.2 0-12.0 0-4.0 0-8.9 0-16.6 0.3-8.1

Cellulosic 

Components

Average 66.7 62.0 54.9 59.2 63.9 66.4 58.3 77.5

Range 61.3-72.3 53.8-67.5 46.8-73.6 - - - - 75.3-80.5

Adjusted 

Cellulosic 

Composition

Average 75.4 70.0 60.5 63.2 72.5 70.1 61.8 83.7

Range 68.9-82.8 61.2-75.8 50.5-84.4 - - - -

77.4-88.6

In the July 2014 rule, EPA considered the cellulosic content of energy cane. Like biomass 

sorghum, cane can be bred for a wide range of cellulosic and sugar contents. In that rule, EPA 

defined “energy cane” as cultivars containing at least 75% adjusted cellulosic content. EPA also 

indicated that in the future, feedstocks that could be bred for a wide range of uses and fiber 

content would have registration requirements similar to energy cane, in order to demonstrate that 

the adjusted cellulosic content of varieties used is at least 75%. Therefore, for the purposes of 

the cellulosic content issue, EPA intends to treat biomass sorghum similar to energy cane. For 

purposes of the Notice, we consider biomass sorghum to include varieties containing at least 

75% adjusted cellulosic content. 

 

REFERENCES

1 Maughan, M.W. (2011). “Evaluation of switchgrass, M. x giganteus, and sorghum as biomass 

crops: Effects of environment and field management practices.” Ph.D. Dissertation, University of 

Illinois at Urbana-Champaign.
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2

Propheter, J.L., S.A. Staggenborg, X. Wu, and D. Wang (2010). “Performance of annual and 

perennial biofuel crops: Yield during the first two years.” Agronomy Journal, 102(2):806-814. 

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Pennington, D. (2011). “Photoperiod sensitive sorghum for bioenergy.” Michigan State 

University Extension. Accessed December 9, 2014, 

http://msue.anr.msu.edu/news/photoperiod_sensitive_sorghum_for_bioenergy

 

4 Rooney, W.L. (2009). “Sorghum Feedstock Performance Tests.” AgriLife Research. 

PowerPoint, Texas A&M University.

5 Olson, S.N. et al. (2012). “High biomass yield energy sorghum: developing a genetic model for 

C4 grass bioenergy crops.” Biofuels, Bioprod. Bioref., 6:640-655.

6 Cherney, J.H. et al. (1990). “Evaluation of potential herbaceous biomass crops on marginal 

crop lands: 1) Agronomic potential.” ORNL/Sub/85-2741/5&P1. Oak Ridge National 

Laboratory, Oak Ridge, TN. 

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Johnson, K.D., J.H. Cherney, D.K. Greene, and J.J. Volenec (1992). “Evaluation of switchgrass 

and biomass sorghum potential.” Oak Ridge National Laboratory, Oak Ridge, TN.

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Turhollow, A.F, E.G. Webb, and M.E. Downing (2010). “Review of sorghum production 

practices: Applications for Bioenergy.” Oak Ridge National Laboratory, Oakridge, TN. 

Available at: http://info.ornl.gov/sites/publications/files/Pub22854.pdf

9 Blade Energy Crops (2010). “Managing high-biomass sorghum as a dedicated energy crop.” 

Available at: http://www.bladeenergy.com/Bladepdf/Blade_SorghumMgmtGuide2010.pdf.

10 Grisso, R. et al. (2010). “Predicting Tractor Diesel Fuel Consumption.” Virginia Cooperative 

Extension, Publication 442-073.

11 Intergovernmental Panel on Climate Change (2006). “N2O emissions from managed soils, and 

CO2 emissions from lime and urea application.” 2006 IPCC Guildelines for National 

Greenhouse Gas Inventories, Volume 4: Agriculture, Forestry, and Other Land Use. Eggleston, 

H.S., Buendia, L., Miwa, K., Ngara, T., and Tanube, K (eds). Published: IGES, Japan.

12 Dahlberg, J., E. Wolfrum, B. Bean, and W.L. Rooney (2011). “Compositional and agronomic 

evaluation of sorghum biomass as a potential feedstock for renewable fuels.” Journal of 

Biobased Materials and Bioenergy, 5:1-7. Additional data provided by J. Dahlberg on October 

22, 2013. 

13 National Renewable Energy Laboratory (2011). “Standard Biomass Analytical Procedure.” 

Accessed December 9, 2014, http://www.nrel.gov/biomass/analytical_procedures.html
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14 Stefaniak, T.R., J.A. Dahlberg, B.W. Bean, N. Dighe, E.J. Wolfrum, and W.L. Rooney 

(2012). “Variation in biomass composition components among forage, biomass, sorghumsudangrass and sweet sorghum types.” Crop Science, 52:1949-1954.

15 NexSteppe (2014). “14-10-09 NexSteppe EPA submission.” Docket EPA-HQ-OAR-2014-

0537.