Switchgrass ( Panicum virgatum L.) is a native warm-season grass and it is one of potential bioenergy crops. The objectives of this study were to: 1) assess the best performing switchgrass genotype suitable for Kansas soil and climatic condition in the USA, 2) determine the correlation between plant height or tiller numbers per plant and dry biomass of various switchgrass genotypes, and 3) assess a bioconversion efficiency of certain varieties of switchgrass. Twenty-two different genotypes of seedlings were allowed to grow in cones for 30 days under controlled environments. The genotype Cave-in-Rock was the shortest among the genotypes. Significant difference in number of tillers per plant was observed among the genotypes. The genotypes Alamo recorded the highest numbers of tiller plant -1 and the genotype Cave-in-Rock had the lowest numbers of tiller plant -1 compared with other genotypes. The genotypes Alamo, NL 94 C2-2, NL 94 C2-3, NSL 2009-1 and NSL 2009-2 had increased above ground biomass compared with other genotypes. The correlation study indicates that there was a significant positive correlation between number of tillers per plant and per plant dry weight (R 2 = 0.93), number of tillers per plant and plant height (R 2 = 0.94), and plant height and per plant dry weight (R 2 = 0.82). Based on the biomass composition, the SWG 2007-2 genotype was the promising switchgrass line for the bioconversion through the sugar platform route due to high carbohydrate and low lignin content. On the other hand, the high biomass yield per unit area of field in NL 94 C2-1 led this genotype with the highest total carbohydrate yield per unit area of field despite the lowest total carbohydrate content in the genotype. These results are pertinent for crop breeders to develop the most promising switchgrass line with high biomass yield and high bioconversion efficiency to produce biofuel through the sugar platform route.
Biomass is a term for all organic material that comes from plants such as trees and crops. Biomass has always been a major source of energy for mankind and is presently estimated to contribute to the order 10% - 14% of the world’s energy supply [
Seeds of twenty two accessions of switchgrass from Oklahoma State University were sown in trays under greenhouse conditions and transferred into cones after emergence at the Kansas State University North Farm in Manhattan, KS, USA in 2010. Metro-Mix 250 growing medium (Scotts-Sierra Horticultural Products Co., Marysville, OH) were used for small pot trial in the greenhouse. In the first two weeks, the seeded pots were watered every day and placed in a tray filled with about 5 cm water. As soon as seedlings grew up to about 5 cm tall, they were transplanted into a 2.5 cm cone trainer and watered until they were transplanted in 2010.
Soils for transplanting were prepared, tilled and leveled to good soil for easy transplantation and establishment. Transplanting was done manually in May, 2010. After transplantation, field was irrigated using sprinklers for 7 days. All the accessions were established well. Sixty kilograms of nitrogen fertilizer per ha was applied about 15 d after establishment. Each plot consists of 6 columns (south to north direction), and a spacing between two neighboring columns is 30 cm. Ten plants were included in each column. A spacing between two neighboring plants in a column is 30 cm. Plot size was 5.4 m2 (6 column × 0.3 m × 10 plants per column × 0.3 m).
Switchgrass samples were measured and collected in late October in 2011 and 2012. Plant height and number of tillers per plant were measured in five randomly selected plants from each replication. Single plant was hand-harvested and dried in air-forced oven at 50˚C for 7 days and dry weight was recorded and dry weight was expressed as dry matter g plant−1. Switchgrass was harvested with 15 cm stubble height.
The biomass composition was evaluated for five selected switchgrass genotypes, whose biomass yields were ranging from 1062.1 g∙m−2 to 1441.5 g∙m−2; biomass yields of these selected genotypes were more than the average biomass yields of 22 genotypes (978.5 g∙m−2). The selected genotypes were NSF 2009-2, NL 94 C2-1, NL 94 C2-3, SWG 2007-2, and Kanlow. Biomass composition was analyzed for total carbohydrate polymers (glucan + xylan + arabinan), total lignin (acid-soluble lignin + acid-insoluble lignin) and total extractives (water-so- luble extractives + ethanol-soluble extractives) contents using standard protocol [
Average temperature and monthly precipitation are listed in
Fisher’s protected LSD was used for multiple comparisons (α = 0.05) [
Significant difference in plant height was observed among the genotypes (
Item | 30-Year | Departure from average | ||
---|---|---|---|---|
Month | Average | 2011 | 2012 | |
Temperature, ˚C | March | 6.4 | +0.3 | +8.3 |
April | 12.5 | +0.8 | +3.0 | |
May | 18.4 | −0.4 | +2.1 | |
June | 23.6 | +1.5 | +3.3 | |
July | 26.6 | +3.2 | −1.0 | |
August | 25.5 | +1.7 | −0.8 | |
September | 20.4 | −1.3 | −0.8 | |
October | 13.6 | +1.4 | +2.7 | |
Precipitation, mm | March | 63.3 | −29.5 | +6.6 |
April | 80.5 | −17.3 | −30.7 | |
May | 129.3 | +1.8 | −102.1 | |
June | 144.8 | −23.6 | −60.9 | |
July | 112.3 | −59.4 | −97.5 | |
August | 104.7 | −45.5 | +2.3 | |
September | 87.1 | −50.0 | −45.5 | |
October | 68.3 | −12.5 | −54.1 |
Entry name | Plant height (cm plant−1) | Number of tillers per plant | Above ground biomass (g∙m−2) |
---|---|---|---|
NSL 2009-1 | 195.9 | 18.1 | 1470.1 |
NSL 2009-2 | 160.4 | 20.7 | 1199.6 |
NSL 2009-3 | 186.6 | 22.7 | 709.5 |
NSL 2009-4 | 179.6 | 16.4 | 1193.5 |
SL 93 C2-1 | 191.4 | 22.0 | 1218.8 |
SL 93 C2-2 | 193.9 | 21.3 | 1034.1 |
SL 93 C2-3 | 186.8 | 21.1 | 1025.8 |
SL 93 C2-4 | 178.4 | 21.5 | 945.5 |
NL 94 C2-1 | 188.7 | 20.1 | 1441.5 |
NL 94 C2-2 | 191.4 | 19.2 | 1387.1 |
NL 94 C2-3 | 186.1 | 18.8 | 1322.5 |
NL 94 C2-4 | 190.4 | 21.5 | 1077.5 |
SNU 98 LMBP C1-1 | 119.8 | 11.3 | 455.5 |
SNU 98 LMBP C1-2 | 140.3 | 17.3 | 504.5 |
SNU 98 EMBP C1-3 | 110.1 | 13.7 | 510.8 |
SWG 2007-1 | 177.7 | 20.0 | 1204.5 |
SWG 2007-2 | 186.6 | 20.6 | 1062.1 |
SWG 2007-3 | 126.5 | 14.9 | 473.8 |
SWG 2007-4 | 145.2 | 16.9 | 534.1 |
Alamo | 176.5 | 24.4 | 1146.5 |
Kanlow | 170.3 | 15.2 | 1082.5 |
Cave-in-Rock | 124.2 | 14.3 | 526.5 |
Mean | 168.5 | 18.7 | 978.5 |
LSD (α = 0.05) | 26.1 | 5.9 | 301.8 |
C2-1, SL 93 C2-3 and SWG 2007-2. The Cave-in-Rock is one of the oldest switchgrass variety bred in Illinois in 1958 and it showed the shortest height among the genotypes of switchgrass.
Significant difference (P < 0.05) in number of tillers per plant was observed among the genotypes ranging from 14.3 to 24.4. The genotype Alamo recorded the highest numbers of tiller plant−1 (24.4) which was on par with NL 94 C2-1, NL 94 C2-4, NSL 2009-2, NSL 2009-3, SL 93 C2-1, SL 93 C2-2, SL 93 C2-3, SL 93 C2-4, SWG 2007-1 and SWG 2007-2. The genotype Cave-in-Rock had the lowest numbers of tiller plant−1 (14.3) compared with other genotypes. Cave-in-Rock variety had a phenotype of both shortest height and lowest numbers of tillers compared to other genotypes.
The genotypes Alamo, NL 94 C2-2, NL 94 C2-3, NSL 2009-1 and NSL 2009-1 had increased above ground biomass compared with other genotypes. The genotypes SWG 2007-3, SNU 98 LMBP C1-2, SNU 98 EMBP C1-1, Cave-in-Rock and SWG 2007-4 had significantly (P < 0.05) lower above ground biomass than other genotypes of switchgrass. On average, a genotype NL 94 C2 that also had both taller plant and more tillers per plant had significantly higher above ground biomass than other genotypes (
In 2012 (two years after transplanting), plant height was taller than those in 2011 by on average 17%. A genotype SNU 98 LMBP C1 (av. 168 cm) showed significantly shorter than NSL 2009 (213 cm), SL 93 C2 (214 cm), NL 94 C2 (215 cm), and SWG 2007 (195 cm). A variety Cave-in-Rock was significantly shorter than other genotypes such as NSL 2009, SL 93 C2, NL 94 C2, SNU 98 LMBP, and SWG 2007. However, no difference in height was found in Alamo, Kanlow, and Cave-in-Rock. Number of tillers per plant in 2012 ranging from 16.7 to 28.3 was significantly higher than those in 2011 by on average 17%, which is very similar to a height change from 2011 to 2012. A genotype SL93 C2 (28.3) had the highest tiller numbers per plant and SWG 2007-4 (16.7) the lowest. Switchgrass biomass was found to be related to number of phytomers per tiller and rate of phytomer development [
Aboveground biomass ranging from 703 to 1615 g∙m−2 in 2012 (
This indicates that as time went by, switchgrass plant size became bigger. Switchgrass has rhizomes, which might have resulted in more tillers and higher above ground biomass. Although Kanlow and Alamo are lowland ecotypes, their average yields over 2011 and 2012 were higher than Cave-in-Rock (highland ecotype). Lowland ecotypes also require a longer growth period [
The correlation study (data not shown) indicates that there was a significant positive correlation between number of tillers per plant and per plant dry weight (R2 = 0.93), number of tillers per plant and plant height (R2 = 0.94), and plant height and per plant dry weight (R2 = 0.82). This study might help bioenergy crop breeders develop certain genotypes that can have high biomass with both high number of tillers per plant and taller plant characteristics.
Entry name | Plant height (cm plant−1) | Number of tillers per plant | Above ground biomass (g∙m−2) |
---|---|---|---|
NSL 2009-1 | 219.1 | 24.0 | 981.7 |
NSL 2009-2 | 210.3 | 23.3 | 1615.5 |
NSL 2009-3 | 220.6 | 20.4 | 888.1 |
NSL 2009-4 | 204.2 | 22.1 | 881.5 |
SL 93 C2-1 | 226.8 | 20.2 | 848.5 |
SL 93 C2-2 | 217.0 | 25.9 | 850.5 |
SL 93 C2-3 | 212.4 | 20.8 | 1146.0 |
SL 93 C2-4 | 203.2 | 28.3 | 1240.9 |
NL 94 C2-1 | 213.0 | 20.5 | 1278.2 |
NL 94 C2-2 | 223.9 | 21.4 | 953.1 |
NL 94 C2-3 | 203.9 | 24.2 | 1428.1 |
NL 94 C2-4 | 220.9 | 20.0 | 1204.7 |
SNU 98 LMBP C1-1 | 166.4 | 18.6 | 1006.4 |
SNU 98 LMBP C1-2 | 183.3 | 19.4 | 1100.0 |
SNU 98 EMBP C1-3 | 156.8 | 18.3 | 618.3 |
SWG 2007-1 | 209.9 | 26.6 | 1277.4 |
SWG 2007-2 | 209.3 | 25.2 | 1593.5 |
SWG 2007-3 | 182.6 | 25.0 | 830.3 |
SWG 2007-4 | 178.5 | 16.7 | 972.6 |
Alamo | 199.7 | 26.8 | 884.3 |
Kanlow | 200.7 | 23.9 | 703.2 |
Cave-in-Rock | 176.2 | 23.5 | 908.5 |
Mean | 201.8 | 22.5 | 1055.1 |
LSD (α = 0.05) | 23.0 | 6.1 | 420.8 |
amount of total lignin, thereby making this genotype the least favorable feedstock for biofuel production through sugar platform route.
If the biomass composition data in
In addition, the NL 94 C2-1 genotype had the highest amount of extractives (14.8% w/w); more than 50% of which were non-structural sugars (glucose, sucrose and fructose). If the non-structural sugar content was included in the total carbohydrate yield per unit area of field calculation, this genotype would have even higher yield. However, further study is needed to confirm the best genotype for bioconversion of switchgrass to produce biofuels.
It is because the bioconversion efficiency depends on a number of factors in addition to gross composition of biomass, including crystallinity of cellulose, lignin structure, and type of linkages among and within the biopolymers (cellulose, hemicellulose and lignin) [
The genotypes, SL 93 C2-2 was the tallest and Cave-in-Rock the shortest among the 22 genotypes. The genotypes Alamo recorded the highest numbers of tiller plant−1 and a genotype Cave-in-Rock had the lowest numbers of tiller plant−1. The genotypes Alamo, NL 94 C2-2, NL 94 C2-3, NSL 2009-1 and NSL 2009-1 had increased above ground biomass compared with other genotypes. The genotypes SWG 2007-3, SNU 98 LMBP C1-2, SNU 98 EMBP C1-1, Cave-in-Rock and SWG 2007-4 had lower above ground biomass than other genotypes of switchgrass. The correlation study indicates that there was a significant positive correlation between number of tillers per plant and per plant dry weight (R2 = 0.93), number of tillers per plant and plant height (R2 = 0.94), and plant height and per plant dry weight (R2 = 0.82). The SWG 2007-2 genotype switchgrass had the highest amount of total carbohydrate polymers and the lowest amount of total lignin; therefore, this genotype is the most promising switchgrass line for the bioconversion to produce biofuel through sugar platform route. On the other
Entry name | Total carbohydrate (g/g biomass) | Biomass yield (g∙m−2) | Total carbohydrate yield (g∙m−2) |
---|---|---|---|
NSL 2009-2 | 0.582 ab | 1199.6 | 698.2 |
NL 94 C2-1 | 0.565 b | 1441.5 | 814.4 |
NL 94 C2-3 | 0.579 ab | 1322.5 | 765.7 |
SWG 2007-2 | 0.594 a | 1062.1 | 630.9 |
Kanlow | 0.566 b | 1082.5 | 612.7 |
hand, the Kanlow genotype had the lowest amount of total carbohydrate polymers and highest amount of total lignin. This study helps bioenergy crop breeders develop certain genotypes that can have high biomass with both high number of tillers per plant and tall plant characteristics and high bioconversion level in switchgrass.
Min, D., Guragain, Y.N., Prasad, V., Vadlani, P.V. and Lee, J. (2017) Effects of Different Genotypes of Switchgrass as a Bioenergy Crop on Yield Components and Bioconversion Potential. Journal of Sustainable Bioenergy Systems, 7, 27-35. https://doi.org/10.4236/jsbs.2017.71003