Potential Yields of sweet sorghum for bioethanol production

by   Anna Fragkidou

July 12, 2025

To estimate sugar content in juice, a refractometer is used for the Brix (%) measurement. Handheld light refractometers and battery powered digital refractometers can be utilised. A model that automatically compensates for temperature should be used. Brix numbers from 14 to 20% would be considered acceptable levels for harvesting. Obviously, the higher the sugar content in the stalks, the higher the potential ethanol yield.

Table 1 and Table 2 present data on various varieties of sweet sorghum according to their yields.

Units

Theis

M-81E

Wray

Keller

Brandes

Rio

Fresh material

mt/ha

125

128

106

107

89

82

Stalk

mt/ha

95

89

76

76

62

52

Fermentable sugars

mt/ha

10.6

9.6

10.3

10.5

6.4

6.2

Ethanol

l/ha

6,159

5,607

5,981

6,131

3,696

3,617

Seeds

kg/ha

6,674

6,213

1,426

1,960

3,500

2,866

Table 13 Variety - Metric Units[i]

Varieties

Total dry matter (ton/a)

Percent stalk1 %

Stalk moisture %

Brix2

Fermentable carbohydrate yield3 (ton/a)

Calculated ethanol yield4 (gal/a)

Stalk lodging5 (%)

Northrup King 301

9.4

52

68

13.2

1.81

247

47

Rox Orange

10.6

46

75

10.3

1.84

250

33

Northrup King 405

11

60

70

7.3

1.25

170

70

Keller

10.1

70

72

13.4

2.96

403

97

Dale

10.0

70

74

12.3

3.00

408

98

Northrup King 8361A

11.7

67

70

8.9

1.85

252

72

M81E

10

66

73

12.7

2.83

385

96

Northrup King 8361

13.1

68

73

7.4

1.96

267

93

LSD (.05)

1.5

3

3

1.7

0.49

66

18

Table 2: Varietal differences in total dry matter yields, percent stalk, stalk moisture, Brix, fermentable carbohydrate yield, ethanol yield and stalk lodging of sorghum and corn grown at Waseca, MN, 1987. [ii]

  1. Dry matter basis.
  2. Brix is approximately equivalent to percent sugar.
  3. Brix multiplied times stalk sap yield.
  4. Assuming 2.5 gal of ethanol/bu of corn grain and 14.7 lb fermentable carbohydrate/gal of ethanol.
  5. Stalk lodging: percent of plants lodged at least 450or more at harvest. Lodging was much more severe in 1987 than 1988 due to two wind storms.

Α two-year study[iii] was conducted in Northern Greece, the objective of which was to assess the productivity (biomass, juice, total sugar and theoretical ethanol yields) of four sweet sorghum cultivars (Sugar graze, M-81E, Urja and Topper-76-6), one grain sorghum cultivar (KN-300) and one grass sorghum cultivar (Susu) grown under Mediterranean conditions. The results of this study indicated that sweet sorghum provides sufficient yields even when grown under stress of soil salinity and reduced irrigation. Sweet sorghum plants produce sufficient juice, total sugar and ethanol yields in fields with soil sanity up to 3.2 dS m-1 even though the plants receive 50-75% of the water regimes typically applied to sorghum. Therefore, sweet sorghum may be viable as an alternative crop system for bioethanol production under increased salinity and reduced irrigation conditions, especially in semi-saline and semiarid Mediterranean fields where the irrigation water is limited during crop development. The following Table indicates the results

Salinity (dS m-1)

Irrigation (mm)

Cultivar

Fresh biomass (Mg ha-1)

Dry biomass (Mg ha-1)

Juice (Mg ha-1)

Brix degree (%)

Total sugar (Mg ha-1)

Theoretical ethanol (L ha-1)

3.2

120

Sugar graze

49.9

16.1

14.3

13.2

1.47

3591



M-81E

61.2

23.7

22.5

10.2

1.75

3354



Urja

48.4

15.8

13.9

12.1

1.33

3225



Topper-76-6

35.5

13.0

14.0

11.1

1.15

2087



Suzu

23.5

9.3

4.2

11.2

0.37

1433



KN-300

38.5

11.5

7.5

11.9

0.68

2451


Irrigation effect


42.8

14.9

12.7

11.6

1.13

2690


210

Sugar graze

88.6

27.6

28.3

13.5

2.98

6528



M-81E

86.5

31.0

30.2

11.5

2.71

5447



Urja

97.3

33.5

34.4

14.4

3.86

7620



Topper-76-6

78.4

27.1

29.1

11.4

2.60

4926



Suzu

30.4

10.9

6.0

11.5

0.54

1913



KN-300

47.2

13.8

10.1

10.2

0.80

2615


Irrigation effect


71.4

24.0

23.0

12.1

2.25

4842

Salinity effect



57.1

19.4

17.9

11.9

1.69

3766

6.9

120

Sugar graze

40.8

12.6

12.2

13.1

1.25

2909



M-81E

43.2

16.4

12.3

10.1

0.95

2375



Urja

39.6

13.3

10.8

11.4

0.95

2454



Topper-76-6

26.9

11.7

9.8

11.2

0.82

1598



Suzu

18.7

7.2

2.7

12.5

0.26

1264



KN-300

29.7

9.0

5.3

11.8

0.47

1850


Irrigation effect


33.2

11.7

8.9

11.7

0.78

2075


210

Sugar graze

67.2

20.5

20.5

13.2

2.13

4870



M-81E

60.4

20.9

20.9

10.6

1.78

3626



Urja

54.6

18.5

17.1

13.1

1.79

3982



Topper-76-6

47.8

15.0

16.0

11.7

1.51

3246



Suzu

19.9

8.1

2.9

11.7

0.27

1271



KN-300

36.6

10.3

8.0

10.2

0.64

2031


Irrigation effect


47.8

15.6

14.2

11.8

1.35

3171

Salinity effect



40.5

13.6

11.5

11.7

1.07

2623

CV, %



18.0

18.1

20.8

8.9

21.0

18.9

Table 3: Fresh &dry biomass yields, , juice yields, Brix degree of juice, total sugar yield and theoretical ethanol yields . Source: Sweet sorghum productivity for biofuels under increased soil salinity and reduced irrigation, Ioannis Vasilakogloua, Kico Dhima, Nikitas Karagiannidis, Thomas Gatsis


[1] Carla E. Shoemaker and David I. Bransby, Auburn University, Department of Agronomy and Soils,“ The Role of Sorghum as a Bioenergy Feedstock”

xi FAO China

xi Putnam, Lueschen, Kanne and Harverstad. University of Minnesota. A Comparison of Sweet Sorghum Cultivar and Corn for Ethanol Production. Submitted for publication in the Journal of Production Agriculture.

xi “Sweet sorghum productivity for biofuels under increased soil salinity and reduced irrigation”, I Vasilakoglou, K Dhima, N Karagiannidis, Thomas Gatsis- Field Crops Research, 2010 – Elsevier, available online 21 September 2010.