Sorghum as an Energy Source

R. E. Schaffert and L. M. Gourley*

The use of sweet sorghum for energy production,principally ethanol production, is discussed. Anexample of an integrated food, feed, energy, andbiofertilizer system is presented. As sorghum isone of the most efficient plants in terms ofphotosynthesis and as sorghum directly producesfermentable sugars as well as grain, it is one ofthe most ideal crops for the simultaneous produc-tion of energy and food. The industrial by-productscan be used as feed, biofertilizer, fiber, andenergy. Technology for ethanol productionadapted from the sugarcane industry can beutilized almost directly to produce ethanol fromsweet sorghum. The additional adaptation of thistechnology for use in a microdistillery allows foreconomical small-unit production in a decentral-ized industry. Transportation costs are reducedand the alcohol is generally consumed by theproducer. The process can be completely mecha-nized or not, depending upon the need to gener-ate jobs and the cost of labor. Production levelshave been considered and research recommenda-tions for this decade have been made.

Energy Crisis

Since 1973 when the petroleum cartel OPEC,initiated a series of price increases and morerecently with mounting political instability amongseveral OPEC members, much emphasis hasbeen placed on alternate and renewable energyresources and energy independence. Energyprices have increased considerably and energy,

* Sorghum Specialist, Interamerican Institute of Cooper-ation for Agriculture. National Com and SorghumResearch Center, Empresa Brasileira de PesquisaAgropecuaria (EMBRAPAl. Caixa Postal 151, 35700Sete Lagoas,MG, Brazil; and Professor of Agronomy,Mississippi State University, P.O. Box 5248, Missis-sippi State, Mississippi, USA. respectively.

principally liquid fuels, has been rationedorconsiderably taxed to reduce their use in nearly alithe petroleum importing nations. This has rnod-ified the economies of nearly ali the nations of theworld and has increased food costs in general,and frequently reduced food and feed production,making it more costly and difficult to feed theworld's millions, especially the world's hungry.

Biomass

In many parts of the world, especially the develop-ing nations, one alternative to the energy crises isthe production of bioenergy from biomass. In thetropical and subtropical areas. and to a lesserextent the temperate areas of the world, anintegrated food, feed, biofertilizer, and energyproduction system using sweet sorghums [$or-ghum bicoior (L.) Moenchl and high energysorghums (Miller and Creelman 1980) along withother crops appears to be an economical andlogical response for adequate food and energyproduction.

This paper will concentrate on the aspect ofsorghum as a renewable resource for liquid fuel orethanol production and treat to a lesser degreesome possible integrated food and energy svs-tems.

Ethanol-A RenewableEnergy Resource

Ethanol has been produced by man since earlyrecorded history as a constituent of fermentedbeverages. Ethanolas a liquid fuel was used in theearliest automobiles. Henry Ford's early auto-mobiles had carburetors that could be adjusted touse either gasoline or alcohol. Since the early1900s Brazilhas used ethanol mixed with gasolineto utilize surplus alcohol from the sugar industry

International Crops Research Institute for the Semi-Arid Tropics. 1982. Sorghum in the Eighties: Proceedings of the InternationalSymposium on Sorghum. 2-7 Nov 81, Patancheru, A.P.• India. Patancheru. A.P. India: ICRISAT.

605

and during the World Wars ethanol was used inplace of gasoline.

lhe attractions of alcohol for fuel are many. lheworld's oil reserves are concentrated in just a fewcountries. while the potential for producing alco-hol from energy crops is as widely diffused asagriculture itself. Liquid fuel from biomass is arenewable resource. Alcohol as a fuel is clean-burning when used alone and when mixed withgasoline it acts to increase the octane rating.Energy crops production and alcohol distillationwill require more labor than oil production andrefining andthus aid unemployment problems andmass migration to the cities. Because of thetransportation limitations of sugar crops. distiller-ies will be decentralized and dispersed throughoutthe crop production area.

Alcohol fuel has a powerful political appeal togovernments and the common motorist. lheproblem of balance of payments. possible oilsupply disruptions. and rising gasoline pricespromote political action toward self-sufficiency. Inthe United States. which has 40% of the world'sautomobiles and which uses half of ali thegasoline consumed in automobiles. political press-ures to produce liquid fuels domestically areparticularly strong.

National Energy Policies

Among the countries already producing ethanolfor fuel. Brazil is the unquestioned leader. Brazil's

alcohol fuel program was launched in 1975. lhegoal to become self-sufficient in automotive fuelby the end of the century has been upgraded tothe end of the eighties. Government incentivesinclude financing to help modernize and expandexisting alcohol distilleries. to build new distiller-ies. and to develop agricultural projects to supplythem with feedstock. lhe national alcohol fuelprogram is based principally on sugarcane. butalso emphasizes sweet sorghum and cassava asdistillery feedstock. In 1981/82 Brazilwill produceapproximately 5 billion liters of ethanol and thetarget is 11.5 billion liters by the end of 1985. In1981 the BrazilianGovernment officially approvedthe extablishment of microdistilleries with acapacity of up to 5000 liters of alcohol/day. lhegovernment's goal is to install 5000 microdistiller-ies by 1985. lhese microdistilleries. which func-tion most economically using both sugarcane (6months) and sweet sorghum (4 or 5 months) (Fig.1) for a total of 10 or 11 months per year. will bescattered throughout Braziland the alcohol will beconsumed in the locality in which it is produced.

lhe first United States alcohol fuel programcame with the enactment of the Energy Act of1978. This legislation removed the federal gaso-line tax of four cents on every gallon of gasohol.provided the alcohol used in the blend was fromnonpetroleum sources. Many states have alsomade gasohol tax exempt which when combinedwith the federal exemption amounts to a totalsubsidy of more than $1 per gallon for ethanolused as automotive fuel.

Sweet sorghum

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

Planting

Harvesting

Sugarcane

Planting

Harvesting

Figure 1. Planting and harvesting periods for sweet sorghum and sugarcane in Brazil (CNPMSIEMBRAPA).

606

Table 1. United States Department of Energy Pro-jections of annual maximum ethyl alcoholproduction in the U.S.

Source1980 1990 2000

(billions of liters)

CornGrains. totalSugarcaneSweet sorghum

8.714.8

3.410.62.6

11.4

8.72.6

31.4

Source: U.S. Department 01 Energy (1979).

Table 2. Alcohol yield of selected crops in theUnited States and Brazil in 1977.

Crop

Crop yieldper hectare

(tonnes)

Alcohol yieldper hectare

(litersl

Sugarcane (Brazil)Sweet sorghum (US)Corn (U.S.)Cassava (Brazil)Grain sorghum (U.S.)Wheat (US)

54.246.5

5.711.9

3.52.1

36303554220021371362

773

Source: Brown (1980).

In January 1980, the federal governmentannounced major new ethanol goals for both 1981and the mid-eighties. Production of ethanol was tobe increased to 1.89 billion liters for fuel in 1981and 7.57 billion liters by the mid-eighties. Sincecorn is the primary distillery feedstock in the U.S.,this latter goal would expend more than 20 millionmetric tons of corno

The U.S. Department of Energy (1979) isconsidering a major shift from corn to sweetsorghum to produce ethanol (Table 1). For thelong-term forecast. it is believed that sweetsorghum could become the dominant energy cropin the United States. A total of 5.67 millionhectares of cropland could be planted to sweetsorghum, which would yield 31.4 billion liters ofethanol per year. This cropland would be primarilyin the Midwestern and the Southeastern UnitedStates.

Many other countries are developing nationalalcohol fuel programs to reduce their balance-of-payment deficits. Table 2 shows the crop and

ethanol yields of selected crops. New Zealandplans to use sugar of fodder beets as the primarydistillery feedstock, while Australia and Austriawould use wheat. South Africa and the Philippinesare planning to use both cassava and sugarcaneas raw materiais for the production of alcohol.Kenya and Sudan are building alcohol distilleriesthat will use the molasses by-product of theirsugar mills. Thailand plans a flexible agriculturalfuel industry that could be adapted to whatevercrop might be in greatest surplus. These are but afew of the countries involved in alcohol fuelprograms. The future is bright for a crop, such assorghum, that will produce reasonable yields ofalcohol per hectare on marginal lands with mini-mum production costs. For the present, mostcountries will use surplus crops or divert somecurrent crop production to alcohol fuel programs.Future programs will bring idle or new marginallands into the production of sugar crops.

Sweet Sorghum-A RenewableBioenergy Resource

Types and Compositionof Sweet Sorghum

Sweet sorghum grows in a wide geographicalrange. It can be considered the sugarcaneof thetemperate zone and it also has a productioncapacity equal or superior to sugarcane in thetropics when considered on a monthly basis.Twotypes of sweet sorghum have been developed bybreeders: syrup varieties which contain enoughinvert sugars in the juice to prevent crystallization,and sugar varieties which contain mostly sucroseand very little invert sugars in the juice forcrystallization. Estimated approximate composi-tions of sweet sorghums grown in the UnitedStates are shown in Figures 2 and 3 for sugarandsyrup varieties, respectively. Sugarvarieties have50% fermentable solids and 30% combustibleorganics while syrup varieties, on the other hand,have 43% fermentable solids and 33% combusti-ble organics. Total biomass yield of syrup varietiesis about 30% more than that of sugar varieties;however, the total soluble solids content of sugarvarieties is greater. This difference in productionand composition may be due to the narrowgenetic base of varieties evaluated,as the numberof sugar varieties availableis much fewer than thenumber of syrup varieties. Both types of sweet

607

Sweet sorghumsugar varieties

I• •907 kg 363 kg

sorghum leaves, pendunele,stalks and heads

I N itrogen produets 4.5%

I Ash 7.2Ether extraet, wax, ete • 2.1• • Solubles 61.0

984 kg 286 kg Fiber 25.2--water dry matter 100.0%

I.- -.(kg) (kg)12.8 nitrogen produets 72.0 fiber16.5 ash 4.1 ash

5.9 ether extraets 15.6 solubles attaehed to fiber158.6 unattaehed solubles --

91.8 insolubles193.8 soluble sol id

I I• • • -., 142.7 kg j 51.2 kg , 87.7 kg j 4.1 kg

fermentab le nonfermentable eombustible ash

solids solids organ ies

c ::::; -u sable for fue l

Average yields: Tonnes/ha

StalksLeaves, pedunele,

and heads

32.9

Total

13.6

46.5

Figure 2. Estimated approximate composition ot sweet sarghum sugar varieties in the United States(Nathan 1978).

sarghum are equally suitable for alcohol produc-tion as both sucrose and invert sugars are directlyfermentable.

because it is adaptable to a wide range of growingconditions. unlike sugarcane which can only begrown in tropical and subtropical climates. Sweetsorghum also has a potential for low unit costsbecause it requires less water and fertilizer thandoes sugarcane. More energy will be recovered inthe ethanol produced than is used to grow andprocess the crop. that is. it has a net energy ratio

Advantages of Sorghum Biomass

Sweet sorghum holds a great potential as a fieldcrop for ethanol production throughout the world

608

Sweet sorghumsyrup varieties

I•• •••907 kg 363 kgsweet leaves, pedunele,

sorghum and headsstalks N itrogen 8.6%

I I Ash 7.81 Ether extract , wax, ete. 2.6

••• • Solubles 52.1Fiber 28.9

984 kg 286 kgwater dry matter 100.0%

I~ ~

~k.f.~ n i trogen prod uets à~~~fiber

17.8 ash 4.4 ash135.5 solubles (unattached] 13.4 solubles attaehed to fiber--7.4 ether extraets, waxes 100.4 insolubles185.3 soluble solids

I I.- •• •• •••121.9 kg 63.4 kg 95,9 kg

fermentable nonfermentable eombustible 4.4 kgsugars and solids organies ash

srarcnes t: : : :t usebte tor fue l

Average yields: Tonnes/ha

StalksLeaves, pedunele,

and heads

47.4

19.3

Total 66.7

Figure 3. Estimated approximate composition ot sweet sarghum syrup varieties in the United States(Nathan 7978).

that exceeds 1.0 (Sheehan et aI. 1978).The desirable characteristics of sweet sor-

ghum varieties for ethanol production are:(1) production of a high biomass yield; (2) highpercentage of fermentable sugars along withcombustible organics; (3) comparatively shortgrowth period; (4) tolerance to drought stress;

(5) relatively low fertilizer requirements;(6) production of grain for food or feed use; and(7) the possibility of complete mechanization.

Sorghum-A C. Pathway PlantSweet sorghum is classified as a C. malate-former

609

Table 3. Maximum dry matter productionand maximum growth rates of several crops.

Dry matter Average growth Maximum growthproduction Maturity rate rate

Crop (tlha) (days) (gm/m2 per day) (qrn/rn? per day)

Napier. 106 365 26Sugarcane 70 365 18 38Sugarbeet 47 300 14 31Forage sorghum 30 120 22Forage sorghum 43 210 19Sudangrass 33 160 18 51Alfafa 36 250 13 23Bermudagrass 35 230 14 20Alga 44-74 300 15-22 28

Source: Loomis and Williams (1963)

which, along with sugarcane and com, is knownto have the highest rate of photosynthesis amongcrop plants. lhe C. pathway of CO2 fixation is anauxiliary channel of the primary Calvin-Bensonpathway (Hatch 1976). Under natural conditions,C. plants are not light-saturated, have CO

2com-

pensation points near zero, lack detectable photo-respiration, and have an optimum temperature of30-35°C.

One of the most important features of C. plantsis their specialized leaf anatomy (Krantz-type)which provides the spatial compartmentalizationrequired to absorb and fix low concentrations ofatmospheric CO2 in two separate sets of reac-tions. Atmospheric CO2 is fixed by the C. pathwayonly in the leaf mesophyll cells while the Calvin-Benson cycle fixes CO

2predominantly in the leaf

bundle sheath cells. lhe net effect in C. plants isthat they exhibit a very high photosyntheticcapacitywhich is about twice as great as that of C

3

plants. Any CO2

produced by photorespirationmust diffuse out through bundle sheath cells andthen through the actively fixing, but nonphotores-piring, mesophyll tissue before it could escapeinto the atmosphere and be detected by existingmethods of measuring photorespiration. This ofcourse leads to greater efficiency in utilizing CO2•

Photosynthetic Efficiency

lhe data of Loomis and Williams (1963) in Table3show that sorghum has one of the highest drymatter accumulation rates when considered on adaily basis. In terms of average growth rate,

610

sorghum is exceeded only by napier grass. In thedata presented by Heichel (1976). sorghum hadthe highest food energy per unit cultural energyratio. exceeding com silage, sugarcane and comgrain. Considering these results. sorghumappears to be one of the most photosyntheticefficient genera that can be produced in bothtemperate and tropical environments, completelymechanized, and utilized on a large scale withexisting technology for energy production. Un-doubtedly, as more attention is placed on bioener-gy production in the future, more attention willalso be given to sorghum.

Technology and Infrastructure forProducing Ethanol from Sorghum

Ethanol from sweet sorghum has been producedin pilot runs in several large-scale commercialsugarcane distilleries of 120 000 liters per day orlarger capacity, and is currently being producedcommercially in several microdistilleries of 2000-5000 liters per day capacity, in Brazil. In bothcases the flow diagram is similar, and twoprocesses for microdistilleries will be consideredhere. lhe differences between microdistilleriesand distilleries of large-scale capacity are: thenumber of units of roller mills, the efficiency ofextracting sugars, and the efficiency of fermenta-tion and distillation.

In Brazil. the normal harvesting period forsugarcane is from June to November and theharvesting period for sweet sorghum is fromFebruary to May with plantings beginning in

October and November (Fig 1). In this case, thetwo crops supplement one another and whenused together increase the period of industrialoperation, decrease the unit cost of alcoholproduction, and increase the total amount ofalcohol that can be produced by a distillery in oneyear. The same equipment is used to processboth sugarcane stalks and sweet sorghum stalks.Consequently, little interest is given to the super-ior productivity of sugarcane or sweet sorghumbut rather an economic production of both sugar-cane and sweet sorghum.

Sugar Extraction Using Roller MiIIsA simple flow diagram of a microdistillery usingroller mills for sugar extraction is shown in Figure4. The stalks of either sweet sorghum or sugar-cane are crushed in the roller mills and the sugarsextracted with the juice. The efficiency of juiceand sugar extraction depends upon the pressureof the rollers and the number of units. When twoor more units are used, the efficiency can be

Hot water

Bagasse

improved by using a small amount of hot water forimbibition. The efficiency also depends upon thenature of the stalk and this will be discussed in thesection on plant breeding and improvement. Theuntreated juice is mixed with yeast and minerais,and is fermented. After the sugars have beentransformed to alcohol, the beer is distilled to92% ethanol for direct use in motors or to 100%ethanol to mix with gasoline. The bagasse can beburned in the boiler to produce steam or can beused for feed, fiber, or as a cellulose feedstock forother processes. The stillage can be used as abiofertilizer and returned to the soil or used as afeedstock in a biodigestor to produce methaneand biofertilizer.

Sugar Extraction by DiffusionA simple flow diagram of a microdistillary using asimple horizontal diffusor for sugar extraction isshown in Figure 5. The major difference in thesetwo processes is the use of hot water to extractthe sugar from the stalks in the diffusor. A roller

Juice

B

Water

Stillage

Figure 4. A simple flaw diagram af a roller mill micradistillery. A-raller mill, B-bailer, C-veasttreatment and distributian tank, D-juice distributian tanks, E- fermenta tian tanks,F-beer-halding tank, and G-distillatian calumn (CNPMSIEMBRAPA).

R11

Sweet sorghum ~ __ ~Sugarca ne • ~. '-r'---->,d-..lo&---"I:t-~--'

Juice

'6~-+-Water

1---++-'---+ A Icoho I

~::::J---+Sti Ilage

Figure 5. A simple flow diagram of a diffusion microdistil/ery. A-forage chopper, B-diffusor,C-rol/er mil/, O-boiler, E-yeast treatment and distribution tenks. F-juice distributiontanks, G-fermentation tsnks, H-beer-holding tanks, and I-distil/ation column (CNPMS/EMBRAPA).

mill is still necessary for removing the residualjuice from the bagasse. An additional roller millmay also be placed before the diffusor for greaterefficiency of sugar extraction. lhe efficiency ofsugar extraction in this process is generallygreater than 90% and equivalent to large-scalesugarcane distilleries.

Sweet SorghumProductivity and Quality

Sweet sorghums or sorgos for syrup productionhave been produced in the USA for over 100 yearswhereas the technology to produce sugar (sue-rose) from sweet sorghum on a commercial scalehas been available for only the past 10 to 15 years.Research on alcohol production using sweetsorghum is even more recent and for the mostpart has been conducted during the last 5 years.Both types of sweet sorghum serve to producealcohol but good types to produce alcohol do notneed to be associated with high sucrose purity ofthe sugar types or the quantity and quality of

612

syrup produced per ton of stalks of the syruptypes. lhe total amount and extraction of totalinvert sugars (fermentable sugar) is important foralcohol production.

Sweet Sorghum Productivitylhe most complete sweet sorghum productivitydata are from the U.S. Sugar Crops ResearchStation of the USDA at Meridian. Mississippi. theTexas Agricultural Experiment Station at WeslacQ,Texas and the National Corn and Sorghum Re-search Center at Sete Lagoas, Minas Gerais,Brazil. According to Reeves (1976). Reeves et aI.(1978). Reeves and Smith (1979). Broadhead et aI.(1974). Coleman and Broadhead (1968). andSchaffert and Borgonovi (1980). average totalyields of commercial varieties over locations andyears normally range from 45 to 60 tlha and 35 to48 t/ha for stripped stalks. According to Schaffertand Borgonovi (1980a) and Reeves and Smith(1979) experimental breeding lines and progenieshave been more productive, with yields rangingfrom 80 to 100 ti ha of sorghum (total plant).

Table 4. Comparison of juiee quality between sweet sorghum and sugareane in Brazil.

Sweet sorghum Sugarcane(São Paulo

State averageslTrait National trialsLiterature

Juice extraction (%1Retractometer BrixSucrose (% juicelInvert sugars (% 'juicelTotal invert sugars (% juice)

350-60016-2010-151-4

14-20

500-70014-208-16

0.7-7.314-18

600-80018-2115-18

0.2-1.516-19

Source: Schaffert and Borgonovi (1980b).

These yields have been with maturity typesranging between 110 and 140 days. Reeves andSmith (1979) have reported yields surpassing 100t/ha fresh weight with longer maturity types.Under optimum large-scale field operations.Schaffert and Borgonovi (1980b) have reportedtotal fresh weight yields exceeding 80 ti ha with130 to 140 day maturity types. Grain yieldsnormally range between 1.5 and 5.5 t/ha withaverage yields between 2 and 3 t/ha.

Sweet Sorghum QualityAlcohol from sweet sorghum is currently pro-duced with technology and equipment used toprocess sugarcane and during the next few yearswill probably continue to be processed this way.Alcóhol or liquid fuel production from biomass inthe future may include technology to utilize thecellulose fraction directly in the processo Thediscussion here will be primarily limited to theparameters dealing with ethanol production usingsugarcane technology. In Table 4. sweet sorghumand sugarcane juice quality are cornpared, Thequality of juice from sorghum is slightly inferior tojuice from sugarcane. but then suqarcane has hadthe advantage of a substantially longe r period ofresearch than sorghum.

Schaffert and Borgonovi (1980b) have obtainedaverage values of juice extraction (Table 5) using ahydraulic press (250 kg I em' for 60 sec) rangingfrom 45 to '76% in a collection of 55 varietiesoriginating from the germplasm collection atMeridian. Mississippi. Percent fiber in the samematerial ranged from 10 to 27%. The values ofBrix and total invert sugars were relatively low asthe material was sampled within a short span oftime and at different stages of maturity. The

variety Wray appears to be one of the mostpromising varieties for both commercial use andin a breeding programo Figures 6-9 demonstratethe interrelationship between the curves of refrac-tometry Brix of the juice, total invert sugars in thejuice extraction. fiber. and total invert sugarextraction for the varieties Wray. Rio. Brandes.and CMSTx 623. respectively. In Figures 10-13the differences between these four cultivars.grown in Brazil. for refractometry Brix. total invertsugars in the juice. juice extraction. fiber. and totalinvert sugar extraction are shown. In Figure 13.the period for industrial utilization (PIU) for Wray ismuch superior to Rio and slightly superior toBrandes and CMSTx623. PIU is the period oftime that total invert sugar extraction of a cultivaris the greatest and at an economical leveI. Wraygenerally has an acceptable PIU exceeding 40days. whereas Rio generally has an acceptableperiod of less than 20 days. This difference is notdue to the quantity of total invert sugars in thejuice. but rather to differences in juice extractionand percent fiber (Fig. 12). Wray is a superiorvariety for both the stalk crushing and the diffusorprocess of sugar extraction. The varieties Brandesand CMSTx 623 also have values more desirablethan Rio; Reeves and Smith (1979) have obtainedbetween 2 and 4% starch in dry stalks ofsorghum. Smith (personal communication. USDA.Texas Agriculture Experiment Station. Weslaco.Texas. 1978) has reported similar values of starchin the juice extracted from stalks. This starch doesnot interfere in the fermentation and distillationprocess but could be hydrolized and converted tosim pie sugars before fermentation. Figure 14demonstrates the major potential uses of sweetsorghum for food. fiber. fertilizer. ethanol andmethane gas production. The only phase untested

613

Table 5. Average values of Brix, total invert sugars, juice extraction, and fiber of selected sweet sorghumvarieties grown at Araras, São Paulo, Brazil in 1981.

Total invertsugars Extraction Fiber

Variety Brix (% juice) (% sorghum stalk) (% sorghum stalk)

Brandes 16.7 14.7 63.2 12.5Honey 130 111 730 11.6Sart 14.7 12.4 69.8 14.8Rio 16.4 14.2 57.6 16.1MN 150b 14.2 11.4 61.1 18.5

MN 1048 14.1 13.4 56.5 220MN 1030 15.2 10.0 47.6 25.8MN 4008 10.6 10.5 74.9 12.0Williams 13.5 12.4 70.5 to.iMN 4080 14.1 45.7 26.6

Wray 19.3 16.8 67.5 14.8Theis 16.4 14.2 71.5 14.8Redlan 10.5 7.4 67.0 13.6Tx623 10.8 7.0 64.0 13.6

Source: Schaffert and Borgonovi 11980bl.

(80)2CMS X S 616 (Wray)

*-0;*~ c;;: .~ (70)1it;

<liUl ~~ )(~II>::l li>Ul U

8rix (% iu ice)"c<li

*9.0 -co•.u

8.0 ~)(

<I>

7.0 ~glJl

x

ài6.0

(50)

85 90 95 100 105 110 115 120 125 130 135 140 145Days after planting

150

Figure 6. The interaction of refractometry Brix and percent total invert sugars in the juice and percentfiber. percent juice extraction. and percent sugar extraction of sorghum stalks during thematurity phase for the variety Wray grown in Brazil (CNPMSIEMBRAPA).

at the National Com and Sorghum ResearchCenter in Brazil is the hydrolysis of the bagasse. Inthe case where this system is integrated with agreenhouse system. the CO, from the fermenta-tion could be used to increase the CO, concentra-

tion in the greenhouse. The biofertilizer can alsobe used in a greenhouse system. Figure 15demonstrates an integrated rural energy systemdeveloped at the National Com and SorghumResearch Center in Brazil that can operate on a

614

"O iBO)20c

'"*'di*,.a.- cu.o-';;(70)15*,U

'".. ~~ •..'" )(ali)

" li)•• u

~'::'(60)102-)(

BR 500 (Rio)

Brix (% juice)

~9,0 c

o•..u

8,0~)(li)

7 ,O ~

"Ch

6,0

(50)0~---'r---.----.----.----'~--.----'----.----r----'---~----'-~~5,O85 90 95 100 105 110 115 120 125 130 135 140 145 150

Days after pla'nting

Figure 7. The interaction of refractometry Brix and percent total invert sugars in the juice and percentfiber, percent juice extraction, and percent sugar extraction of sorghum stalks during thematurity phase for the variety Rio grown in Brazil (CNPMSIEMBRAPA).

(80)20"OclU

*'di*.a.- c.•. o (70)15~~.. ~~ •..lU )(ali)

"•• li)

- .~(60)10!! z.0-•..)(

BR 501 (Brandes)

9,0~c

8,0 o•..u'"•..

7,0 )(li)

'"a6.0 ~

(50)5 ~-L-.r---'-----r----r---.-----r---,----,----,----.----,----~--~5,O100 105 110 115 120 125 130 135 140 145 15085 90 95

Figure 8. The interaction of refractometry Brix and percent total invert sugars in the juice and percentfiber, percent juice extraction, and percent sugar extraction of sorghum stalks during thematurity phase for the variety Brandes grown in Brazil (CNPMSIEMBRAPA).

planning purposes in Brazil.Agricultural yields canbe much higher than 37.7 metric tons of stalksand 2.2 metric tons of grain per hectare undergood management. The average industrial yieldsare those obtained by large industrial operationsand are currently about 20% less for microdistiller-ies. Utilizing both the grain and the stalks toproduce alcohol, one hectare will produce 3387liters of ethanol in 4 months. The utilization of one

zero petroleum and electrical energy input basis.Many other options are also possible for totalutilization of the sorghum plant.

Economics of ProducingAlcohol from Sorghum

Table 6 shows the range and average yields ofsweet sorghum and ethanol production used for

615

(80)2

"c:.,

;;;*:e c:(70)15- o~'gUI ~~~'"xaCl>::JUI CI>_.~ (60)1~ .~0-~.x

cXi

CMS X S 623(8randes Derivative)

9.0

c:8.0 o•..

o~

7.0 ~CI>~'"6.0 ~cn

(50) 5~----r----.---.r----.--~----.---~----.---~----.----r--~.---~~ 5.0

85 90 95 100 105110 115120 125130 135140 145 150Days after planting

Figure 9. The interaction of refractometry Brix and percent total invert sugars in the juice and percentfiber. percent juice extraction. and percent sugar extraction of sorghum stalks during thematurity phase for the variety CMSXS 623 grown in Brazil (CNPMSIEMBRAPAj.

20.0

17.5

CI> 15..~'".!!!XI

CI>~ 10.aCI>O

7.5CMS X S623

Rio

5.0

01 /~'-rl----rl----TI----.----,----.----.-----r---,r----r----.---~----._--~--~ I I I I I I I I iO 85 90 95 100 105 110 .115 120 125 130 135 140 145 150

Days after planting

Figure 10. The differences between four cultivars grown in Brazil for refractometry Brix of the juiceduring the maturity phase of production (CNPMSIEMBRAPA).

ratoon crop would increase this value by 50-80%. Table 7 shows the production costs ofethanol from sweet sorghum stalks in Brazil inNovember of 1980 considering two levels of stalkproduction and three industrial production levels

616

representing three types of microdistilleries. onecrushing unit. two crushing units and a diffusionunit respectively. Horizontal and vertical diffusionunits for microdistilleries are currently being evalu-ated in Brazil.

Table 6. Agricultural and industrial yields of sweet sorghum in Brazi!.

Agricultural Alcohol yieldyield

Component (t/ha) (liter/t) (liter/ha per harvest)

Stalks Range 22-66 55-85 1210-5610Average 37.7 70 2639

Grain Range 1.4-6.6 310-370 434-2442Average 2.2 340 748

Total Range 1644-8052Average 3387

Source: Schaffert and Borgonovi (1980b).

Table 7. Production costs of alcohol from sweetsorghum in Brazi! in microdistilleries,November 1980.

Item US$

Production costs/haCost/t stalks (30 t/ha)Costlt stalks (40 t/ha)

Cost/I alcohol (45 liter/t and 40 t/ha)Cost/l alcohol (59 liter/t and 40 tlha)Cost/l alcohol (68 liter/t and 40 t/ha)

32010.678.00

0.220.200.17

Source: CNPMS/EMBRAPA, Caixa Postal. 151. 3570ü-Setelagoas. MG. Brazil.

17.5

:12.5CDCI::IUI-10 O!! 'o•.•.; 7,6~.,11.

5,0

Future Sorghum BiomassResearch and Development

Development of Improved Cultivars

Insensitivity to Photoperiodism

One of the factors limiting sorghum biomassproduction in the tropics and subtropics is thesensitivity of most of the cultivars to photoperiod-ism. This seriously limits varietal management fora prolonged harvest period of several months.Two principal sources for insensitivity used in theBrazilian sweet sorghum improvement program

Wrav

Riorandes

O ~~<~Ir---'I----~Ir---'Ir----Ir----rl----rl----rl----TI----,~----,---~I-----Ir---_rl--85 90 95 100 105 110 115 120 125 130 135 140 145 150

Davs after planting

Figure 7 7. The differences between four cultivars grown in Brazil for total invert sugars of the juiceduring the maturity phase of production (CNPMSIEMBRAPAj.

617

20.0(80)

ê17.5(75)o

Rio

CMSXS623

-===::~~:::::::::=:===:==:=:~wraY_ Brandes

~~~

~u~ 15.0(70)(

"~12.5(65)~"el0.0(60)"ticca~ 7.5(55)"~.•..'"

5.0(50)

"uO~/" I I ICL

B5 90 95

BrandesCMSXS623WrayRio

I I i I I I i I I I100 105 110 115 120 125 130 135 140 145 150Days after planting

Figure 12. .The differences between four cultivars grown in Brazil for juice extraction and fiber of thestalks during the maturity phase of production (CNPMSIEMBRAPA).

11.0

10,0

*-- 9.0co~~ 8,0~)(

"~ 7,0::l

Vl

6,0

90 100 105 110

5.0~----~---r----~---'-----r----~---.r----r----~---'-----r~~~--~~----

15095 115 120 125Days after plant ing 130 135 140 145

Figure 13. The differences between four cultivars grown in Brazil for total invert sugar extraction of thestalks during the maturity phase of production (CNPMSIEMBRAPA).

are the varieties Wray and Honey. The varietiesBrandes. Theis. Dale, Roma, ·and Ramada are alivery sensitive and the variety Rio is intermediatein reaction.

Disease and Insect Resistance

Cultivars with good levels of resistance to foliardiseases are needed to maintain a high percen-

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tage of green leaves until harvest to improve thebiological value of the bagasse for animal feed.The varieties Brandes and Wray have adequatelevels of disease resistance in Brazilian conditionsbut are susceptible to Cercospora sorghi. Resist-ance or immunity to the sugarcane mosaic virusesis necessary for cropping adjacent to sugarcane.Good insect resistance is also necessary, espe-cially resistance to the sugarcane borer (Diatraeaspp),

Sweet sorghum

o ístl Ilation

Ethanol

Figure 14. The potential uses of sweet sorghum for food, fiber, iertilizet, ethanol, and methane gasproduction (CNPMSIEMBRAPA).

619

.,c:Õ '"s:s: •..o .,.!:! §.

'";. I/)

'"s:'"•..ow

'"

Ethyl alcoholStillage and bagasse

Electric ity Biogas

Figure 15.

Otheruses

An integrated rural energy svstem developed at the National Com and Sorghum ResearchCenter of EMBRAPA in Brazil (CNPMS/EMBRAPA).

Male-sterile Sweet Sorghum Lines

A new series of A andB sweet sorghum lines isneeded to produce hybrids. Hybrids producedwith the available A-lines are significantly moreproductive but the juice quality is reduced and thelevei of total invert sugars is more variable than forcommercial cultivars. Lines such as Redlan, Tx622, Tx 623 and Tx 624 have not producedadequate hybrids. The cost of hybrid seed produc-tion is much less than the cost of variety seedproduction due to harvest costs.

Maturity Groups

New cultivars with varying maturity lengths,100-210 days, are needed to improve varietalmanagement for a longer total harvest period.Most cultivars produced in the tropics normallyreach maturity between 110 and 140 days.

Improved Industrial Quality

Cultivars with greater total sugars, lower fiber,

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and greater sugar extraction, as well as cultivarswith a longer PIU are needed.

High Energy ~orghum

High energy sorghums, as proposed by Miller andCreelman (1980). with high potential levels ofgrain production and large quantities of ferment-able sugars in their stalks should be developed.This will provide a greater range of processingsystems that can be employed for food, feed, andenergy production.

Stress Tolerance

It is necessary to develop sorghums for biomassproduction that are more tolerant to mõisturestress, toxic aluminum stress. and acid soil stressso that these can be grown in the marginal landsthat are acid, with toxic levels of aluminum, andare subject to moisture stress. In Srazil alonethere are more than 180 million hectares of landwith these characteristics that are not currently incrop production.

Development of Basic Studies

Seedling and Initial Growth Rates

Sweet sorghums are slow starters, they haveslower growth rates than grain sorghum for thefirst 20-30 days of growth. The factors assoei-ated with this trait need to be identified to allowbreeders to develop fast starters.

Herbicide and Insecticide Resistance

Sweet sorghums are generally much more sus-ceptible to chemical damage than other sorghumsand grasses. Sources of resistance need to beidentified for utilization in a breeding programoTheuse of protection agents mixed with the seed togive a greater range of herbicide use is alsoneeded.

Growth Curves

The development of growth curves associatedwith sugar metabolism and accumulation isneeded as well as studies to determine theoptimum stalk size for maximum sugar productionand maximum sugar extraction during the indust-rial processing phase. Other biochemical andphysiological aspects of sugar production andaccumulation also need to be studied.

Development of ImprovedManagement Practices

Row Spacing and Plant Density

Optimum plant spacing and density studies needto be developed to determine the correct com-bination of total productivity, stalk size, and thethe type of industrial processing. Stalk size andnumber are also important factors in manualharvesting efficiency.

Date of Planting Studies

Regionaldate of planting trials for adapted culti-vars are necessary for optimum varietal manage-ment.

Mechanization

The lack of adequate planting equipment neces-

sary for uniform stands is a limiting factor in manyof the tropical areas of the world and adequateplanting and management systems need to bedeveloped. Systems of mechanized harvest orsemimechanized harvest compatible with theindustrial process need to be developed.

Weed Control

Adequate weed control systems need to bedeveloped. The use of seed protection agents forgreater herbicide choice and combinations ofmechanical and chemical control methods needtobe developed and improved.

Ratooning

Production systems utilizing one or two ratoonharvests need to be developed. Until recently,with the introduction of photoinsensitive varietiesratoon cropping was not possible in the short-daytropical environments. Schaffert and Borgonovi(1980a) obtained total production of 166 t/hasorghum in three harvests near Petrolina,Pernam-buco, Brazil with a selection from the varietyHoney in one year. New cultivars and systems forratoon cropping are essential for efficient varietialmanagement.

Fertilizer Calibrations

Fertilizer recommendations need to be developedfor high yielding sweet sorghums where theentire crop is removed and stillage and biofertilizermay or may not be applied to the soil. ReevesetaI. (1978) reported a range of removal of potas-sium from the soil varying from 132 to 515 kg/hafor three sweet sorghum cultivars. The phosphor-us removed was much less and rangedfrom 15to37 kg/ha.

Development of More EfficientIndustrial Processes

The most promising system for the immediatefuture, using sweet sorghum, is the microdistillerywith a capacity ranging from 500 to 5000 liters perday. These are small cooperative or large farmsystems where approximately 10% of the cropland area is needed for zero petroleum energyinputs and where the by-products can be utilizedon the farm. Additional studies of stillage andbiofertilizer rates need to be made for optimum

utilization of these products. Improving the effi-ciency of sugar extraction, cellulose hydrolysis(biodiqestor), fermentation, distillation and heattransfer is important. Technology for more effi-cient utilization of ethanol and biogas in farmmotors is also desirable. The biological values ofthe by-products for animal feed also need to beevaluated. Economical methods to utilize thestarch in the extracted juice for alcohol productionneed to be developed for microdistilleries.

Fuel or Foodor Fuel and Food

Using energy crops as a source of fuel places anew demand on agriculture to produce an adequ-ate food supply. In the 1980s we will see a muchlarger quantity of agricultural resources beingdiverted to the production of nonfood crops thancould have been imagined in the 1970s. Food-exporting countries such as the United States,Brazil, Australia, New Zealand, and South Africaare actively pursuing programs for the conversionof crops into alcohol for fuel on a commercialscale. As oil prices increase, distillers will be ableto increase the price of ethanol and will becomecompetitive in grain markets. The use of sugarcrops for liquid fuel will also compete for theworld's cropland to a large extent. The use ofsweet sorghum for liquid fuel production does notneed to be a question of fuel or food but rather anoption of fuel and food.

Conclusion

If the production of large quantities of ethanol forfuel from sugar crops becomes a reality, thefuture of sweet sorghums in the eighties andbeyond indeed looks bright. Sorghum breedersmust utilize the tremendous genetic diversity ofthis genus and direct breeding efforts towarddeveloping improved varieties and hybrids as acrop for fuel and agronomists must developproduction systems for the many industrial op-tions available for processing sweet sorghum.

Acknowledgments

The authors wish to thank PLANALSUCAR (theSugarcane Improvement Authority of Brazil) inAraras, SP for their support of sweet sorghum

622

research and analysis of samples for the maturitycurves presented in this paper. and the NationalCorn and Sorghum Research Center (CNPMS) ofEmpresa Brasileira de Pesquisa Agropecuaria(EMBRAPA) for other important data used.

References

BROADHEAD,D. M., FREEMAN,K. C., COlEMAN, O. H., andZUMMO, N. 1974. Theis-a new variety of sweetsorghum for syrup production. Mississippi Agriculturaland Forestry Experiment Station Information Sheet1236. Mississippi State, Mississippi, USA: MississippiState University.

BROWN,L. R. 1980. Food or fuel: new competition forthe world's cropland. Worldwatch Paper 35. Washing-ton, D. C., USA: Worldwatch Instituté.

COlEMAN. O. H.. and BROADHEAD.D. M. 1968. Brandes. anew variety of sweet sorghum for syrup production.Mississippi State University Agriculture ExperimentStation Information Sheet 1013. State College, Missis-sippi. USA; Mississippi State University.

HATCH.M. D. 1976. The C, pathway of photosynthesis:rnechanisrn and function. Pages 59-81 in CO2 meta-bolism and plant productivitv. eds. R. H. Burris. and C.C. Black, Baltimore. Maryland. USA: University ParkPress.

HEICHEl, G. H. 1976. Agriculture production and energyresources. American Scientist 64: 64-72.

LOOMIS.R. S., and WllllAMS. W. A. 1963. Maximum cropproductivity: an estimate. Crop Science 3: 67 -71.

MlllER. F. R., and CREElMAN. R. A. 1980. Sorghum-anew fuel. In Proceedings. 35th Annual Corn andSorghum Research Conference, American Seed TradeAssociation.

NATHAN,R. A. 1978. Fuels from sugar crops: systemsstudy for sugarcane, sweet sorghum, and sugar beets.Oak Ridge, Tennessee, USA: United States Depart-ment of Energy, Technical Information Center.

REEVES,S. A. 1976. Sweet sorghum research report,1975. Technical Report 76-3. College Station, Texas,USA: Texas Agricultural Experiment Station, TexasA&M University.

REEVES.S. A., HIPP, B. W., and SMITH,B. A. 1978. Sweetsorghum biomass-a renewable energy source. Tech-nical Report 78-1. College Station, Texas. USA: Texas

Agricultural Experiment Station. Texas A&M Univer-sity.

REEVES.S. A.. and SMITH. B. A. 1979. Sweet sorghumbiomass-a renewable energy source. Part 2. Technic-ai Report 79-1. College Station. Texas. USA: TexasAgricultural Experiment Station. Texas A&M Univer-sitv,

SCHAFFERT.R. E.• and BORGONOVI.R. A. 1980a. Sorgo-uma opção para a produção de alimentos e energia. AGranja. 36: 60-64. Editora Centaurus Ltda.. PortoAlegre. Brazil.

SCHAFFERT.R. E.,and BORGONOVI.R. A. 1980b. Perspecti-vas de sorgo sacrino para produção de etanol. In pressin Simpósio sobre álcool. Academia de Ciências doEstado de São Paulo. Brazil.

SHEEHAN.G. C.• GREENFIELD.P. F.• and NICKLlN.D. J. 1978.Energy economics. ethanol-a literature review. InProceedings. Alcohol Fuels Conference. Sydney. Au-stralia.

USDOE (United States Department of Energyl. 1979.The report of the alcohol fuels policy review. Washing-ton. D. C.: U. S. Government Printing Office.

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