evaluating silicon concentrations in biofuel feedstock crops miscanthus and switchgrass

7
Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass Krishna P. Woli a , Mark B. David a, *, Jenwei Tsai a , Thomas B. Voigt b , Robert G. Darmody a , Corey A. Mitchell a a University of Illinois at Urbana-Champaign, Department of Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 S. Goodwin Av., Urbana, IL 61801, USA b University of Illinois at Urbana-Champaign, Department of Crop Sciences, S-416 Turner Hall, 1102 S. Goodwin Av., Urbana, IL 61801, USA article info Article history: Received 19 July 2010 Received in revised form 7 February 2011 Accepted 4 March 2011 Available online 3 April 2011 Keywords: Miscanthus giganteus Panicum virgatum Combustion Precipitation Silicon Temperature abstract Silicon (Si) concentrations in biofuel feedstock crops have a critical role in combustion processes. The purpose of this study was to quantify Si concentrations in plant biomass samples and to evaluate the contributing factors for Si concentrations. We determined total Si concentrations in Miscanthus giganteus (M. giganteus) collected from various research trial plots in the eastern U.S. and in Miscanthus spp. and Panicum virgatum, ‘Cave- in-Rock’ (switchgrass) from an additional eight trial plots established across Illinois. Whole aboveground plant biomass at each site were air-dried and ground. Total Si concentrations in plant samples were determined by dry-ashing plant tissue in a muffle furnace, followed by alkaline fusion and then colorimetric analysis. Average Si concentrations in statewide M. giganteus plant samples ranged from 0.72% to 1.6% and samples from within Illinois ranged from 0.55% to 2.4%. The overall median value of concentrations in M. giganteus samples among all sites was 1.08%. The median value in switchgrass samples (1.5%) was 1.4 times higher than that for M. giganteus. Among six other Miscanthus spp. samples from the Urbana trial plot in Illinois, Si concentrations were about 1/3 that of M. giganteus. Variation in Si concentrations tended to be associated with temperature and precipitation of the location where the biofuel crops are being grown. We did not find any relationship between soil type and plant Si concentrations. Long-term evaluations of soil mineral concentrations and additional environmental factors are required to better understand the contributing factors for Si concentrations. ª 2011 Elsevier Ltd. All rights reserved. 1. Introduction A major fraction of global CO 2 emission is from burning fossil fuels that supply 85% of the total energy consumption [1], and there is growing concern for developing viable alternatives to non-renewable fossil fuels. Direct combustion of biomass is reported to be the most energy-efficient alternative with the highest potential for mitigating the CO 2 emission problem [2]. Biofuels could reduce greenhouse gas emissions by 1.7 billion tons per year, which is equal to more than 80% of trans- portation-related emissions and 22% of total emissions [3]. Relative to the fossil fuels they are capable of displacing, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel [4]. The U.S. Department of Energy has targeted developing biomass conversion technologies since petroleum products are the * Corresponding author. Tel.: þ1 217 333 4308. E-mail address: [email protected] (M.B. David). Available at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 35 (2011) 2807 e2813 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.03.007

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Page 1: Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3

Avai lab le a t www.sc iencedi rec t .com

ht tp : / /www.e lsev ier . com/ loca te /b iombioe

Evaluating silicon concentrations in biofuel feedstock cropsMiscanthus and switchgrass

Krishna P. Woli a, Mark B. David a,*, Jenwei Tsai a, Thomas B. Voigt b, Robert G. Darmody a,Corey A. Mitchell a

aUniversity of Illinois at Urbana-Champaign, Department of Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 S.

Goodwin Av., Urbana, IL 61801, USAbUniversity of Illinois at Urbana-Champaign, Department of Crop Sciences, S-416 Turner Hall, 1102 S. Goodwin Av., Urbana, IL 61801, USA

a r t i c l e i n f o

Article history:

Received 19 July 2010

Received in revised form

7 February 2011

Accepted 4 March 2011

Available online 3 April 2011

Keywords:

Miscanthus � giganteus

Panicum virgatum

Combustion

Precipitation

Silicon

Temperature

* Corresponding author. Tel.: þ1 217 333 430E-mail address: [email protected] (M.B

0961-9534/$ e see front matter ª 2011 Elsevdoi:10.1016/j.biombioe.2011.03.007

a b s t r a c t

Silicon (Si) concentrations in biofuel feedstock crops have a critical role in combustion

processes. The purpose of this study was to quantify Si concentrations in plant biomass

samples and to evaluate the contributing factors for Si concentrations. We determined

total Si concentrations in Miscanthus � giganteus (M. � giganteus) collected from various

research trial plots in the eastern U.S. and in Miscanthus spp. and Panicum virgatum, ‘Cave-

in-Rock’ (switchgrass) from an additional eight trial plots established across Illinois. Whole

aboveground plant biomass at each site were air-dried and ground. Total Si concentrations

in plant samples were determined by dry-ashing plant tissue in a muffle furnace, followed

by alkaline fusion and then colorimetric analysis. Average Si concentrations in statewide

M. � giganteus plant samples ranged from 0.72% to 1.6% and samples from within Illinois

ranged from 0.55% to 2.4%. The overall median value of concentrations in M. � giganteus

samples among all sites was 1.08%. The median value in switchgrass samples (1.5%) was

1.4 times higher than that for M. � giganteus. Among six other Miscanthus spp. samples

from the Urbana trial plot in Illinois, Si concentrations were about 1/3 that of

M. � giganteus. Variation in Si concentrations tended to be associated with temperature and

precipitation of the location where the biofuel crops are being grown. We did not find any

relationship between soil type and plant Si concentrations. Long-term evaluations of soil

mineral concentrations and additional environmental factors are required to better

understand the contributing factors for Si concentrations.

ª 2011 Elsevier Ltd. All rights reserved.

1. Introduction Biofuels could reduce greenhouse gas emissions by 1.7 billion

A major fraction of global CO2 emission is from burning fossil

fuels that supply 85% of the total energy consumption [1], and

there is growing concern for developing viable alternatives to

non-renewable fossil fuels. Direct combustion of biomass is

reported to be the most energy-efficient alternative with the

highest potential for mitigating the CO2 emission problem [2].

8.. David).ier Ltd. All rights reserved

tons per year, which is equal to more than 80% of trans-

portation-related emissions and 22% of total emissions [3].

Relative to the fossil fuels they are capable of displacing,

greenhouse gas emissions are reduced 12% by the production

and combustion of ethanol and 41% by biodiesel [4]. The U.S.

Department of Energy has targeted developing biomass

conversion technologies since petroleum products are the

.

Page 2: Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 32808

most limiting primary fossil energy resources, and conversion

of plant biomass provides the only anticipated renewable

feedstock to generate liquid transportation fuel [5]. The

plant materials-derived fuels can be cost-competitive with

gasoline and diesel, and can reduce global warming emis-

sions, improve air quality, reduce soil erosion, and diversify

agroecosystems [3,6].

Energy and fuels from biomass could provide tremendous

economic, environmental, and energy security. Perennial

grasses are burned to produce heat and electricity or treated

with enzymes, heat, and/or acids to produce sugars that can

then be used to produce cellulosic ethanol [7]. Such grasses

have been termed as biofuel feedstock crops which require

much less energy and financial inputs than annual arable

crops. Miscanthus � giganteus (M. � giganteus) is one of several

ideal biomass crops that can be used to generate heat, power,

and fuel, and can alleviate CO2 emissions [8,9]. It is a perennial

C4 grass with high yield potential [9,10], efficient conversion of

solar radiation to biomass, efficient use of nitrogen and water,

and good pest and disease resistance [11,12], considered as

a low input crop having a low environmental impact

[1,9,12,13]. Among other biofuel feedstock crops, the nitrogen,

energy, and land use efficiencies inM.� giganteus are reported

to be highest at the lowest nitrogen inputs [14]. The ratio

of energy output to energy input in the production of

M. � giganteus is 14.2e19.7 and thus much better than that of

whole grain crops at 8.5 [15]. Compared to other lignocellulose

plants, M. � giganteus biomass is reported to have a good

combustion quality [2].

The mineral concentration of herbaceous biomass has

a great impact on its suitability as a feedstock for thermo-

chemical combustion processes [16,17], and reduced mineral

content at harvest improves the combustion characteristics of

biomass [18]. Thermochemical conversion in a gasification

reactor involves heating the feedstock under restricted

oxygen conditions to produce syngas that is subsequently

converted to an energy product [19]. Biomass quality can

drastically impact the net energy output, both by influencing

the effectiveness of conversion plants and controlling the

heating value [16,20]. At operational temperatures where

carbon conversion efficiency is high, silicon (Si), which is

abundant in grass feedstocks, and sulfur react with aluminum,

chlorine, potassium, and other alkalis to form sticky glass-like

silicates and oxides referred to as slag, along with corrosive

alkali sulfates [21]. These ashes and inorganic elements

produced during combustion react to form slag deposits and

corrosive compounds at temperature in the range of 700 �C[16,22] and may cause a number of serious problems to power

plants through slagging, corrosion, and fouling [20]. Slag

formation and corrosive alkalis increase maintenance cost,

reduce the lifespan and utility of gasifier hardware, and

diminish economic feasibility of converting these feedstocks

to fuel [21]. Although Si can negatively impact thermo-

conversion of biomass to bioenergy, Si has beneficial biolog-

ical effects, including increased plant resistance to lodging

and drought [23], improved disease resistance [24,25], insect

and nematode resistance [26], soil nutrient availability,

nutrient balance within the plant (e.g., N, P, Zn, and Mn),

photosynthesis, improved reproductive fertility, and reduced

transpiration [27].

With respect to the role on the effectiveness of the ther-

moconversion process, minimizing mineral contents and

understanding their controlling factors is important in

a biofuel crop. However, relatively few studies have assess-

ed Si concentration in the heavily studied biofuel crops

M. � giganteus and Panicum virgatum (switchgrass). The

objectives of our study were to quantify Si concentrations and

to evaluate the controlling factors for Si concentrations in

M.� giganteus plant samples that were collected frombiomass

trial plots in the eastern U.S. Silicon concentrations, that were

determined for six other different varieties of Miscanthus spp.

and several ‘Cave-in-Rock’ switchgrass plant samples collected

from various trial sites in Illinois, were also included in the

study for comparison.

2. Materials and methods

The existing research trial plots established by the Illinois

Council for Food and Agriculture Research, University of Illi-

nois Energy Biosciences Institute, and Department of Energy/

Sun Grant Herbaceous Feedstock Partnership were used for

collecting plant biomass samples. M. � giganteus plant

samples were collected from biomass trial plots in Michigan,

Nebraska, New Jersey, Kentucky, Oklahoma, and Mississippi

in January 2010. Similarly, plant samples were collected in

December 2007 from eight Research and Education Centers

located at Dekalb, Havana, Urbana, Orr, Pana, Brownstown,

Fairfield, and Dixon Springs in Illinois. Four 10 � 10 m repli-

cated side-by-side trials of M. � giganteus and ‘Cave-in-Rock’

switchgrass have been established at Dekalb, Urbana, and

Dixon Springs in 2002 and at Havana, Orr, Pana, Brownstown,

and Fairfield in 2004 (Table 1) in Illinois along a longitudinal

gradient at these sites without fertilizer additions to examine

the response of these crops following the conversion from row

cropping [28]. Trial plots of aM.� giganteus fertility study were

established at Nebraska, New Jersey, and Kentucky in 2008

and unfertilized plots at Michigan, Oklahoma, and Mississippi

in 2009. Four sets of plant biomass samples were collected

from each location ensuring one from each replicated plot and

were used for Si analysis. Therefore, we had four replicates

per site, with each replicate analyzed in duplicate (see below).

Soil types ranged from Alfisols at Kentucky and Michigan,

Mollisols at Oklahoma and Nebraska, Ultisols at Mississippi

andNew Jersey to both Alfisols andMollisols at various sites in

Illinois (Table 1).

Whole plant samples were collected randomly from

different replicate plots at the senescence stage of plant

development. The collected plant materials were air-dried

and were ground in a Wiley mill (Arthur H. Thomas Co.,

Philadelphia, U.S.A.) and passed through 40-mesh screen

before analysis.

Total Si concentrations in plant samples were determined

using a ‘modified Hallmark’ procedure (Si determination

technique) developed by Hogendorp [29]. In general, this

technique involved dry-ashing plant tissue in a muffle

furnace, followed by alkaline fusion, and then colorimetric

analysis. Plant tissue samples (25 mg) were ashed in nickel

crucibles without covers at 550 �C for 5 h in a muffle furnace

(Hythermco, Pennsauken, NJ, U.S.A.). Sampleswere left to cool

Page 3: Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass

Table 1 e Physical characteristics of the sites established for Miscanthus fertility study in the U.S., by latitude (north tosouth).

State/Location/Latitude

Planted year Soil type Soil class Mean annualtemperature/precipitation

MI/MSU Kellogg

Biological Station

42.3956359 N

2009 Kalamazoo loam (Alfisols) Fine-loamy, mixed, semiactive,

mesic Typic Hapludalfs

8.9 �C89.3 cm

IL/Dekalb

41.8441175 N

2002 Elpaso silty clay loam (Mollisols) Fine silty, mixed, superactive,

mesic Typic Endoaquoll

8.8 �C94.9 cm

NE/Univ. of Nebraska

41.1720000 N

2008 Tomek silt loam (Mollisols) Fine, smectitic, mesic Pachic

Argiudolls

9.8 �C70.4 cm

NJ/Rutgers Univ.

40.4631173 N

2008 Nixon loam and Sassafras-Urban

sandy loam complex

(Ultisols/Alfisols)

Fine-loamy, siliceous, semiactive,

mesic Typic Hapludults þFine -loamy, mixed, active, mesic

Aquic Fragiudalfs

11.4 �C123.9 cm

IL/Havana

40.2960410 N

2004 Disco sandy loam (Mollisols) Coarse-loamy, mixed, superactive,

mesic Pachic Hapludolls

10.8 �C96.0 cm

IL/Urbana

40.0425649 N

2002 Flanagan silt loam (Mollisols) Fine, smectitic, mesic Aquic Argiudoll 10.8 �C104.3 cm

IL/Orr

39.806104 N

2004 Winfield silt loam (Alfisols) Fine silty, mixed, superactive,

mesic Oxyaquic Hapludalf

10.8 �C97.7 cm

IL/Pana

39.443383 N

2004 Virden silty clay loam (Mollisols) Fine, smectitic, mesic Vertic

Argiaquolls

11.4 �C103.0 cm

IL/Brownstown

38.9500000 N

2004 Hoyleton silt loam (Alfisols) Fine, smectitic, mesic Aquollic

Hapludalfs

11.6 �C106.8 cm

IL/Fairfield

38.3810019 N

2004 Wynoose silt loam (Alfisols) Fine, smectitic, mesic Typic

Albaqualfs

12.2 �C114.3 cm

KY/Univ. of Kentucky

38.1277798 N

2008 Bluegrass-Maury silt loams

(Alfisols)

Fine silty, mixed, active, mesic

Typic Paleudalf þ Fine, mixed,

active, mesic Typic Paleudalf

12.9 �C116.6 cm

IL/Dixon Springs

37.4535770 N

2002 Grantsburg silt loam (Alfisols) Fine silty, mixed, Active, mesic

Oxyaquic Fragiudalf

14.5 �C122.5 cm

OK/Oklahoma State Univ.

35.991500 N

2009 Teller fine sandy loam (Mollisols) Fine-loamy, mixed, active, thermic

Udic Argiustolls

15.2 �C93.2 cm

MS/Mississippi State Univ.

33.424608 N

2009 Marietta fine sandy loam

(close to Ultisols)

Fine-loamy, siliceous, active, thermic

Fluvaquentic Eutrudept

16.8 �C140.8 cm

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3 2809

overnight with the door closed. Two grams of sodium

hydroxide (NaOH) were added to each ashed sample and

immediately heated with a Bunsen burner for 15min to create

a soluble sodium cake. Samples were swirled after first 5 min

of heating for proper mixing of the sample and NaOH. After

letting them cool for about 30min, deionized water was added

up to one-third of the crucible’s volume and let to stand

overnight. The solution of sodium silicate cake was then

transferred to 100 mL volumetric flasks, approximately 50 mL

of deionized water was added and 2 mL of H2SO4 solution was

added using a repeating pipette. After bringing up to the total

volume of 100 mL with deionized water and mixing well, total

Si concentrations (mg L�1) were analyzed on a Lachat Quik-

Chem 8000 flow injection analyzer (Lachat Instruments/Hach

Company, Loveland, CO) at 820 nm absorbance with

a minimum detection limit of 0.15 mg SiO2 L�1. A quality

control check standard (QCCS), representing the approximate

midpoint of the calibration range was included as the first

sample in each set and was repeated following every eighth

sample. All QCCS value determinations were within 10% of

the actual concentration. Each plant tissue sample was

analyzed in duplicate. Three blanks and three samples of San

Joaquin Soil (10 mg) of known value (29.66% Si) as standard

reference materials (U.S. Department of Commerce, National

Institution of Standard and Technology (NIST), Gaithersburg,

MD, U.S.A) were included in each batch of plant samples.

There are no plant reference materials with known Si

concentrations available, and the standard soil was the only

known standardwe could locate. However, we did utilize NIST

pine needle reference material as well, using it as a consis-

tency check from batch to batch, as there is no known Si

concentration given. Volumetrics of 500 mL were used for

standard soil samples to achieve a desired dilution. Analytical

duplicate and spiked samples were also prepared for every

seventh sample in each run to ensure accuracy and a precise

determination. Each of the concentrations of measured Si in

plant samples were adjusted based on the known values for

the standard San Joaquin soil reference material versus the

measured value in each batch, and in some cases with the

pine needle concentration.Most correctionswere<10%, but in

some batches the standard soil or pine needle had consistent

values within the batch, but different than either the known

soil or our established pine needle concentration, leading to

larger corrections. When the difference between duplicate

plant samples and triplicate soil standards exceeded 10% of

the concentration with each other, those samples were

reanalyzed. Calculation of descriptive statistics, two-sample t-

test, and regression analyses were performed in SAS using the

univariate (PROC UNIVARIATE), t-test (PROC TTEST), and

multiple regression (PROC GLM) procedures [30], respectively.

Page 4: Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass

Table 3 e Silicon concentrations in switchgrass plantsamples collected from various trial plots in Illinois.

State/Location

Mean % � sd(n ¼ 4)

Median%

Maximum%

Minimum%

IL/Dekalb 1.58 � 0.21 1.61 1.76 1.33

IL/Havana 1.10 � 0.39 1.04 1.62 0.71

IL/Urbana 1.53 � 0.35 1.43 2.03 1.23

IL/Orr 1.26 � 0.42 1.20 1.74 0.73

IL/Pana 1.49 � 1.49 1.64 1.70 0.99

IL/Brownstown 2.38 � 0.57 2.39 2.94 1.79

IL/Fairfield 1.53 � 0.55 1.43 2.28 0.98

IL/Dixon

Springs

2.18 � 0.40 2.23 2.53 1.71

Overall 1.63 � 0.43 1.53 2.38 1.10

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 32810

3. Results

Silicon concentrations in M. � giganteus plant samples from

across the eastern U.S. ranged from 0.72% to 1.62%. (Table 2).

Among all values, the range of average Si concentrations was

greater for the eight sites in Illinois (0.55%e2.42%). Both the

lowest and highest limits of Si concentrations were thus

observed among trial plots of Illinois. Out of four replicates,

one each in Dekalb and Dixon Springs had very high concen-

trations (3.19% and 4.28%, respectively); exceeding the

maximum value obtained among rest of the samples (data not

shown). The overall mean value of Si concentrations in

M. � giganteus samples among all sites was 1.16% and the

overall median value was 1.08%.

Among the ‘Cave-in-Rock’ switchgrass biomass samples

collected from eight different trial plots in Illinois, the average

concentrations ranged from 1.10% to 2.38% (Table 3). The

upper limit was similar to that of M. � giganteus samples

whereas the lower level was about two-fold greater. Themean

Si concentration in M. � giganteus samples was significantly

lower (P < 0.01) than that in switchgrass (1.63%) and the

overall median value inM. � giganteus samples (1.08%) was 1.4

times lower than that for ‘Cave-in-Rock’ switchgrass (1.53%).

The result of six other types of Miscanthus spp. samples

from the Urbana trial plot in Illinois showed that Si concen-

trations were also highly variable (Table 4), ranging from

0.81% to as high as 3.56%. Themedian value was 2.78%, which

is about three times higher than that for M. � giganteus

samples.

Table 2 e Silicon concentrations in Miscanthus plantsamples from biomass trial plots.

State/Location

Mean% � sd(n ¼ 4)

Median%

Maximum%

Minimum%

MI/MSU Kellogg

Biological

Station

0.72 � 0.11 0.75 0.80 0.56

IL/Dekalb 1.59 � 0.96 1.25 3.19 0.66

NE/Univ. of

Nebraska

0.69 � 0.13 0.68 0.91 0.57

NJ/Rutgers

Univ.

0.88 � 0.13 0.96 0.96 0.73

IL/Havana 0.55 � 0.18 0.54 0.77 0.36

IL/Urbana 1.19 � 0.45 1.26 1.57 0.66

IL/Orr 0.79 � 0.25 0.81 1.00 0.53

IL/Pana 0.80 � 0.27 0.82 1.09 0.47

IL/Brownstown 0.99 � 0.26 0.90 1.43 0.79

IL/Fairfield 1.59 � 0.51 1.59 2.30 1.00

KY/Univ. of

Kentucky

1.62 � 0.33 1.74 1.87 1.14

IL/Dixon

Springs

2.42 � 1.30 1.96 4.28 1.50

OK/Oklahoma

State Univ.

1.20 � 0.08 1.20 1.30 1.08

MS/Mississippi

State Univ.

1.17 � 0.09 1.19 1.25 1.05

Overall 1.16 � 0.51 1.08 2.42 0.55

Multiple regression models were used to evaluate the

genotypeeenvironment interactions among M. � giganteus

and ‘Cave-in-Rock’ switchgrass samples and various factors

such as plant age, soil type, fertility, latitude, and mean

annual temperature and precipitation. The results showed

that there was no significant relationship between any of

these factors and Si concentrations (data not shown).

However, there was a strong tendency of higher Si concentra-

tions in the locationswith low latitude and greater temperature

and precipitation. This tendency was common both for

M. � giganteus and ‘Cave-in-Rock’ switchgrass samples. When

two remarkably higher values of Si concentration in

M. � giganteus samples were excluded, the correlation between

Si concentrations and temperature and precipitation became

significant at 5% level of significance (Fig. 1).

4. Discussion

High variability in mineral concentrations among promising

biofuel crops can be considerable as it depends on genetic and

environmental factors [31] as well as physiological and

morphological difference among crops [14,20]. In this study,

average percentage of Si concentrations in M. � giganteus

plant biomass samples varied widely among the locations.

Previous studies also reported high variability, ranging from

0.46e2.11% [32,33,34]. Another species of Miscanthus (i.e. Mis-

canthus sacchariflorus), had the reported values ranging from

0.55% to 1.42% [32,33,35], but our sample had a much higher

concentration (3.24%). Among the several cultivars of

Table 4 e Silicon concentrations in different genotypes ofMiscanthus plant samples collected from Urbana trialplots in Illinois.

Species Silicon (%)(n ¼ 1)

M. sacchariflorus 3.24

M. sinensis ‘Siberfeder’ 1.69

M. sinensis ‘Graziella’ 0.81

M. sinensis ‘Rigoletto’ 2.75

M. sinensis ‘Zebrinus’ 3.56

M. sinensis ‘Bluetenwunder’ 2.82

Page 5: Evaluating silicon concentrations in biofuel feedstock crops Miscanthus and switchgrass

Mean annual temperature (°C)8 10 12 14 16 18

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Mean annual precipitation (cm)60 80 100 120 140 160

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

)%(

noitartnecnociSy = 0.0122x - 0.2092R2 = 0.31, p < 0.037

y = 0.0926x - 0.0228R2 = 0.32, p < 0.036

a

b

Fig. 1 e Relationship between Miscanthus Si concentrations

at each site and (a) mean annual temperature and (b) mean

annual precipitation.

Table 5 e Silicon concentrations in different species ofMiscanthus and switchgrass in this study and literatures.

Species Silicon (%) Reference

Miscanthus � giganteus 0.62e1.21 [32]

1.42e2.11 [33]

0.46e0.96 [34]

0.55e2.42 This study

(median value ¼ 1.08)

Miscanthus sacchariflorus 1.42 [35]

0.55e0.96 [32]

0.86e0.96 [33]

3.24 This study

Miscanthus sinensis 2.86 [36]

3.20 [35]

0.45e1.67 [20]

0.78e0.86 [32]

1.05e1.33 [33]

M. sinensis ‘Siberfeder’ 1.69 This study

M. sinensis ‘Graziella’ 0.81 This study

M. sinensis ‘Rigoletto’ 2.75 This study

M. sinensis ‘Zebrinus’ 3.56 This study

M. sinensis ‘Bluetenwunder 2.82 This study

Panicum virgatum 0.53e1.57 [20]

2.01 [23]

0.38e1.40 [37]

0.18e2.86 [38]

1.03e5.04 [39]

1.10e2.38 This study

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3 2811

Miscanthus sinensis measured in this study, the concentration

ranged from 0.81% to 3.56% (Table 5), which was similar to the

reported values, ranging from 0.45% to 3.20% [20,32,33,35,36].

‘Cave-in-Rock’ switchgrass also showed a high variability

in Si concentration ranging from 1.10% to 2.38% but the vari-

ability was lower compared to that for Miscanthus spp. A

similar range of Si concentration was reported by Monti et al.

[20], Hodson et al. [36], and El-Nashaar et al. [37] (Table 5). El-

Nashaar et al. [38] studied various elements such as Si, chlo-

rine, sulfur, phosphorus, and potassium in native temperate

grasses grown in thewesternU.S. and reported a greater range

of Si concentrations in switchgrass (0.18e2.86%). Even higher

values were reported by Lanning and Eleuterius [39] ranging

from 1.03% to 5.04% in various parts of switchgrass plants.

Among the studied biofuel feedstock crops switchgrass and

different genotypes of Miscanthus, M. � giganteus grown in

research trial plots of different states had the lowest Si

concentrations (median value 1.08%). This result favors the

suitability of this crop for producing biofuel with efficient

combustion process because lower Si concentration enhances

better thermochemical conversion [18]. Comparing the

combustion quality among coal, straw, wood, cereal, andM.�giganteus, Lewandowski and Kicherer [2] reported that

M. � giganteus biomass had very good combustion quality due

to its low water concentration as well as its low chlorine,

potassium, nitrogen, sulfur, and ash concentrations. It

appeared that M. � giganteus could be a promising biofuel

feedstock crop in the U.S. given its reduced level of Si

concentration together with its superiority in nitrogen and

water use efficiency, good pest and disease resistance [11,12],

and high yield potential [10].

There is not enough known about the contributing factors

to Si concentrations in these biofuel feedstock crops. Visser

and Pignatelli [34] attributed variability in Si concentration

in plant biomass to difference in harvesting methods or in

soil types. Our study did not exhibit apparent relationships

between soil types and Si concentrations in plant biomass. A

previous study also reported that variations in mineral

concentrations including Si in plant biomass samples were

not related to soil chemistry [38]. In a study conducted for

different genotypes of switchgrass in five locations in the U.S.,

El-Nashaar et al. [37] reported that location had a strong

impact on mineral concentrations including Si and latitude of

origin impacted the Cl and Si concentrations in plant tissues.

They reported that the least Si occurred in plants grown at the

two coolest locations of Wisconsin, whereas the greatest Si

concentrations were observed in plants grown in Kansas with

warm mid-summer temperature. Our findings also indicated

that warmer locations with relatively higher precipitation

amount had a tendency of greater Si concentration in both

M. � giganteus and ‘Cave-in-Rock’ switchgrass samples. There

could be a strong influence of location on the biomass quality

due to the influences on the development of the plant, and due

to precipitation, which causes the leaching of minerals [2]. At

locations with temperate climates, soil freezing and thawing

cycles in winter could have potential impact on weathering

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b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 32812

and leaching of soil minerals that could influence mineral

uptake by plants, resulting in greatermineral concentration in

plant biomass. Studies of Si accumulation during heat adap-

tation suggest that warmer temperatures are accompanied by

an increased formation of Si bodies and increased Si-con-

taining leaf pubescence in grasses [40].

5. Conclusions

Among the plant biomass samples of M. � giganteus collected

from six different eastern U.S. states and eight trial plots in

Illinois, ‘Cave-in-Rock’ switchgrass from eight plots in Illinois,

and six different genotypes of Miscanthus in Urbana, M. �giganteus had the lowest level of Si concentrations in plant

tissues, indicating its greater potential with respect to biofuel

quality. Locations with warmer temperature and greater

precipitation generally had higher Si concentrations in plant

biomass. Further research to assess the long-term impact of

soil Si concentrations in different locations and other possible

environmental factors such as magnitude of leaching associ-

ated with duration of snow-cover and freezing-thawing

processes might be of importance and help understand

M. � giganteus, one of the most promising biofuel crops.

Acknowledgments

Funding was provided by the State of Illinois through the

Illinois Council on Food and Agricultural Research (C-FAR),

Biomass Energy Crops Strategic Research Initiative and by

the Energy Biosciences Institute. We thank cooperators for

providing biomass samples.

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