1st Year Progress Report
(for period August 1997 to 31st July 1998)
E. Mvududu (SIRDC-BRI, Zimbabwe)
J. Gopo (SIRDC-BRI, Zimbabwe)
J. Woods (KCL, UK)



Executive Summary

The primary aim of the first year trials was to establish a well-defined process aimed at isolating high potential varieties and hybrids of sweet sorghum developed from various activities around the world with reference to the desired end products i.e. electricity and ethanol. To this end a number of varieties / hybrids have been identified as potential sources of germplasm of sufficient quality for commercial electricity and ethanol production. Other Indian, Indonesia and hopefully Chinese varieties will also be assayed during next year’s trial.

The aim of the trials in the first year and second years is to evaluate sweet sorghum varieties against three basic variables in order to demonstrate that they are capable of being used for the commercial and sustainable production of ethanol and electricity within existing sugar mills. These three criteria are:

The first year trials have already highlighted two varieties as having considerable promise, namely, cv. Keller and cv. Cowley, satisfying the first two evaluation criteria above. Both these varieties produced over 70 fresh weight tonnes of above ground biomass, and crucially are of high biomass quality (fresh weight Pol% of 12. % and 13%, Brix % of 17 and 18 respectively) and ethanol yields of up to 70ml /100kg TRS).

The estimated potential ethanol productivity from sweet sorghum for the best performing varieties is 3500 l ha-1 per crop including likely losses due to harvesting, transport, and processing. In comparison with sugarcane which could produce 7900 l ha-1 yr-1 (365 growing days) sweet sorghums specific productivity of 35 l ha-1 per growing day is nearly 60% higher than sugarcane at 22 l ha-1 per growing day. Because of the slightly higher fibre content of sweet sorghum versus sugarcane, the potential electricity production from sweet sorghum is also higher on a per tonne delivered stems basis. In fact, it is estimated (at a 30% conversion efficiency- energy content bagasse to energy content electricity) that 10.5 MWhe could be produced per ha sweet sorghum. This is sufficient to supply a rural African village (requiring a constant supply of 10 kWe) for 43 days continuous electricity, or 8 ha could theoretically supply this village for a year.

The rest of the varieties, though equally high in biomass quantity, had significantly lower sugar contents.. Crucially, for the best performing varieties, the period taken to reach peak sugar levels was between 3 to 4 months indicating good suitability for industrial processing prior to sugarcane harvesting. The levels of both sugars and fibres are significantly higher than in previous trials. Millability tests of 4 varieties of sweet sorghum carried out at Triangle were a success.

Fermentation tests carried out also show that ethanol yields from sweet sorghum are higher than those obtained from C-molasses currently used by Triangle for ethanol production, Ethanol yields up to 30% greater per unit Total Fermentables.(TF) were obtained from sweet sorghum compared to C-molasses.These fermentability results also suggest that the extraction of crystalline sugar results in the build up of fermentation inhibitor concentrations in the residual molasses, which can reduce fermentation efficiency.

As a result of the first year trials, the project has shown the agronomic potential of sweet sorghum for ethanol and electricity production. During the second year, the project can build on these results and will focus greater attention on the logistics and practicalities of using sweet sorghum in the Triangle Ltd. sugar mill in order to answer questions concerning the period of industrial utilisation, harvesting, transport and juice extraction at a commercial scale.

Assessment of Technical Progress

The primary aim of the first year trials was to establish a well-defined process aimed at isolating high potential varieties and hybrids of sweet sorghum developed from various activities around the world with reference to the desired end products i.e. electricity and ethanol. To this end a number of varieties / hybrids have been identified as potential sources of germplasm of sufficient quality for commercial electricity and ethanol production. Other Indian, Indonesia and hopefully Chinese varieties will also be assayed during next year’s trial.

During September / November 97 land preparation was carried out at the SIRDC (PEA’s) site in Harare and at the Lowveld Research Station site in South Eastern Zimbabwe. In mid-November 1997, 2ha of land were planted to sweet sorghum at the Harare site and 5 ha at the Lowveld Research Station site. This reduction in planted land area resulted from a number of factors; firstly seeding requirements were much heavier than that budgeted for, labour requirements for monitoring the extra land area would have been excessive and because no diffuser test was to be carried out at Triangle, extra land area was not required during first year at Chiredzi. In the coming trial,3ha will be planted, possibly on different blocks from the one planted to the sprinkler-irrigated crop in the previous trial for rotational purposes and the continued evaluation and optimisation of crop growth parameters. Keller and Cowley varieties are to be planted on those 3ha for seed bulking purposes. The drip-irrigated section will be maintained and the next season variety trial is to be planted on this piece of land. Unfortunately the nature of the drip irrigation system set up, makes it immovable hence the same land will be used. It is hoped that 0.5ha will be planted at Triangle, for the purposes of Industrial and or mini-lab scale biomass quality and quantity analysis. The experimental and data gathering protocols were successfully established and good quality data is now available from these trials. (See Trial Report).

In this 1st year trial two varieties have shown considerable promise, namely, cv. Keller and cv. Cowley. Both these varieties have produced over 70 fresh weight tonnes of above ground biomass, and crucially are of high biomass quality in addition to the high productivity levels. The levels of both sugars and fibres are significantly higher than in previous trials and barring problems with the physical consistency of the fibre during crushing and filtering. Crushing tests carried out at Triangle, March 98 were successful. (See Trial report)

Other varieties will continue to be evaluated but seed bulking activities will be concentrated on cv. Keller and cv. Cowley. Further tests are required at Triangle Mill to demonstrate that sweet sorghum juice can be used at a commercial scale for ethanol production and these tests will be run at the end of the 1998/99 trial.

Future Resource Requirements- Land Area. The expansion of trial area at the Lowveld Research Station will allow for an industrial juice extraction test using the Triangle Mill diffuser, in March 1999, which will require a minimum of 200 t sorghum stems or approximately 250 fresh weight tonnes of above ground sorghum biomass.

Requests have been made to allow movement of money between line items without any change to the overall budget. (Dr. Gopo discussion with Lindsay Jolly and Eltha Brown)

Social and Environmental Effects of Project Implementation

To date only positive effects have been derived by the implementation of the project, assisting in the research and development environment of all organisations involved. The employment and on-the-job training received by the two Zimbabwean project employees has been beneficial to them and the organisations through which they are employed.

The project has also employed significant numbers of local personnel, both female and male, at various stages of crop growth, for planting, weeding, bird scaring and for harvesting. .Whilst not directly measurable this "extra" employment has provided a supplementary source of income for the local poorer section of society, especially the women.

Conclusions and Recommendations

The project has been successfully implemented with all tasks and activities being carried out as per the first year work programme. The project achieved it’s aims, and it is encouraging to note that Triangle Ltd (5th March, 1997) did agree to lab-scale and industrial level testing of sweet sorghum as early as the first year, these will be carried out in the second year on a larger scale.

The new varieties of sweet sorghum tried out in Zimbabwe for the first time by this project during this season have exceeded expectations in both productivity and biomass quality. We believe, however that achieving the full potential for these varieties under the prevailing climate and non-limiting conditions requires further work. There is still considerable room for improvement of the agronomic factors governing crop growth and management all of which points towards a strong future for sweet sorghum as a novel source for energy production in the sugar industries of southern Africa and elsewhere. It also essential that a closer look is taken at the economics of utilising sweet sorghum as an energy source.



As part of a 3-year research trial period in Zimbabwe aimed at establishing potential sweet sorghum varieties for ethanol and biomass energy production, five different varieties of sweet sorghum were evaluated in the first year for biomass productivity both in terms of quantity and quality as well as the length of their growing season. Above ground fresh weight ranged from 53t/ha to 84t/ha with dry matter yields of 11t/ha to 20t/ha. Pol of up to 13% was recorded, and purities of between 49% to 84%. It was observed that sugar content was highest between milking and hard dough stage, for all the varieties. Two varieties are showing a good potential namely Keller and Cowley both in terms of quantity and quality of biomass. Of all the varieties tested all proved to be long season varieties, taking approximately135 days to maturity with the exception of Rona –H which exhibited characteristics of an early variety taking 87 days to maturity. Both Keller and Cowley took between 100 to 115 days to achieve peak sugar levels, which then decreased towards maturity. Keller which was planted in Harare exhibited similar growth characteristics to the Keller planted in Chiredzi. The local varieties tested were of low biomass quality. With an average Pol of 4, Brix of 9 and purity of below 50.



Test locality: Lowveld Research Station,Chiredzi (Lat & Long) –21o 03o
Planting date: 17th November 1997
The following 5 varieties Keller, Monori E'des, Rona-H , IS19674 and Cowley were planted in a completely randomised block design with 3 replicates. Plot size was 15m x10m. Other varieties which include, L1 (Chinese variety). R1, R2, R3, R4, R5, were also planted." R" varieties are those collected from the rural areas in Zimbabwe.

2ha of sprinkler irrigated Keller was also planted on ex-potato field

Experimental Plot Layout

Test Location: Harare, Zimbabwe

Planting date: 25 November to 30 November 1997

Keller and Rona-H were planted on in 15m2 x 15m2 plots. Fertiliser: Application was done according to soil analysis results. Compound D was applied at a rate of 300kg ha-1 as a basal fertiliser. Ammonium nitrate was applied at a rate 100kg ha-1 (N). The fertiliser was applied by side banding. Split application of the fertiliser was carried out to minimise losses due to leaching and increase nitrogen use efficiency of the sweet sorghum. The first application was carried on the 14th and 15th of January 1998, after sufficient soil moisture had built up from the precipitation that had occurred on the previous days. The dry spell had little negative effect on the growth of sweet sorghum cultivar, which has reasonable moisture stress tolerance. The terrain of the land, which is uneven, resulted in water logging in some areas of the trial land, this led to nutrient leaching and as a result some plants were showing signs of phosphate deficiency.

Seed source
Forty-three kilograms of Keller seeds were purchased from Transworld Seed

Corporation (United States of America). Two 2 Hungarian Hybrids (1 Kg each hybrid), were obtained from the Gabonatermesztési Kutatóintézet Cereal Research Institute, Szeged, Hungary.Other varieties / hybrids were obtained from China and from existing stores at the Lowveld Research Station. R1, R2, R3, R4, R5, were also planted."R" varieties are Those collected from the rural areas in Zimbabwe.

Soil Analysis: An initial soil nutrient analysis for both the Chiredzi and Harare was carried out on the 18 December and 5 November 1997 respectively. Soil analysis was carried out at ZSA for the two sites. Five sites were sampled randomly within sampling blocks. Five depths were taken per pit at 20cm intervals. Samples from the same depth were mixed and sun dried before being sent for analysis.

Fertilisation Application

Nitrogen applications totaling100kg/ha was applied:

Compound D (7:14:8 N: P2O5:K2O ) minimum 6.5 % Sulphur, granular) was applied at a rate of 300kgha-1 as a basal application. Ammonium nitrate (34.5% N, granular) was applied five weeks after emergence at the rate of 100kg N ha-1. A Split application was carried out at the Harare trial where heavy rains were experienced. The applications were carried out during the 5th and 7th week. No splitting was done at the Chiredzi trial, as there was no danger of leaching due to low rainfall. These fertiliser applications were based on the soil nutrient analysis results as well as recommendations for fertiliser application in Zimbabwean soils, (Farm management handbook, and 1982).


Over the last 5 years a number of sweet sorghum trials have been carried out on the Lowveld Research Station. A drip irrigation system was installed (Netafim- typhoon surface tape system) in 1994 to allow very accurate control of water application for a 0.5 ha section divided into eight 17m x 100m blocks which could be individually irrigated if required. In 1996, this section was extended to a total of 15 irrigation blocks, giving a total area 2.8 ha. The sampling programme is concentrating on the first 10 blocks, however, the remaining blocks were planted with cv. Keller, with another, block being planted as a strictly rainfed block. The Harare trial was strictly rainfed.

Irrigation scheduling was done through the pan evaporation system. (See irrigation sheets)

Disease and pest control

There were isolated cases of stem borer attack and they were controlled through spot application of Thiodan 50% wp . Stalk borer control was carried out on the 1st & 24th January. Aphids were a major problem with the Harare trial; Dimethoate 40% ec was used for aphid control (Table 5.). The high rainfall, which was being experienced also, reduced aphid levels significantly. A large proportion of the pest was washed down and their effect was reduced.


Growth analysis

The 1st row was omitted on every plot. On the 2nd row one metre was also omitted. The 2nd metre on the 2nd row was regarded as the 1st metre. All the plants from this metre were counted and their fresh weight determined. These plants were cut into small pieces and put in viking papers and oven dried at 100oC. Plants on the 3rd metre of the 2nd row are regarded as 2nd metre plants. They were then counted and their fresh weight determined, and the total number of tillers per plant recorded. The 1st 3 plants on the 2nd metre were partitioned, however if one plant is missing then it is not substituted as this results in an overestimation of unit area yield. The number of tillers per plant was then recorded and also partitioned.

On partitioning, fully expanded leaves are separated from expanding. Both expanding and fully expanding leaves had their areas determined using the leaf area metre. Leaf length and width was measured using rulers. Stems of partitioned plants were chopped and oven dried. All the above measurements were are also carried on the tillers taken from the main stems for partitioning. Dead leaves on both the 1st and 2nd metres were also oven dried and the dry weights recorded. Sampling for growth analysis commenced on the 16th of December 1997. Sampling then continued at two weekly intervals. All in all 8 samplings were carried out

For the Harare trial only fresh and dry weight measurements were recorded. Biomass sampling was carried out on the 8th February 1998, the second sampling was carried out on the 2nd April. The 1st row was omitted on every plot. On the 2nd row one metre was also omitted. The 2nd metre on the 2nd row is then regarded as the 1st metre. All the plants from this metre were counted and their fresh weight determined. These plants were then cut into small pieces and put in viking papers and oven dried at 100oC. Five plots were sampled from.

Sugar analysis

Sugar analysis was carried out by the Zimbabwe Sugar Association

Sampling for sugar analysis started at the booting stage for each variety and was carried at weekly intervals up to maturity. Information for every stage starting from booting stage is then compared. The growth stage at which the purity %, Pol % is highest for each variety can then be obtained and recommendations made as regards the best period to harvest Stems of varieties (20-25) were hand harvested by slashing the stalks, and the leaves stripped off. The stems were pushed through a simple crushing mill and the resulting bagasse collected in containers. For fibre percentage the bagasse was oven dried for 24hrs at 110oC using a Labotec oven . For Brix and Pol values the bagasse was blended using a T50 Blender. The resulting filtrate was used for Brix and Pol measurements. The Brix extract % values were recorded using an RFM 500 Refractometer (Bellingham and Stanley Ltd) and for Pol % extract values a Polatronic Universal meter (Schmidt and Haensch) was used. Actual Brix and Pol % values were read off the Schmidt table.

Triangle (Pvt) Limited also carried out a sugar analysis and fermentation test on the same varieties, 17 weeks after sowing at which stage the varieties were thought to have reached peak sugar content going by the Zimbabwe Sugar Association sugar analysis tests results. All four varieties except for Rona-H, which had since reached maturity, were analysed. Fermentation test was carried out according to method No M/002 outlined in the Tongaat-Hulett Sugar Analytical Services Laboratory Manual, courtesy Triangle (Pvt) Limited.


Harvesting is crucial, as it is the interface between agriculture and industry; therefore it was essential that simulation of commercial harvesting and milling be carried out. This also enabled assessment of sweet sorghum milliabilty. Harvesting of the sweet sorghum stems was carried out on the 17th March. The sweet sorghum stems were harvested manually, first the leaves were stripped and the stems cut by machetes and stacked into piles of (2m long and 1.5m high). The stems bundles (3 tonnes each) were mechanically loaded onto a 30t trailer mechanically and transported to Triangle (Pvt) Ltd (approx. 20km in distance) for milling.

Storability tests
In a bid to find the rate of stem deterioration, the following treatments were carried out on the sweet sorghum stems (n=20-30), before being sent for sugar analysis. Samples were sent on two consecutive days.

i) Plants were stripped off their leaves and left standing in the field.

ii) Plants were removed from the field and stems stripped of their leaves

iii) Plants were removed from the field and stored with leaves

Seed bulking
Heads were cut manually and seed was thrashed and winnowed. It was then placed in 21kg containers and treated with phostoxin pellets (a pesticide) and stored in hesian sacks.


Soil nutrient analysis

Chiredzi: The Chiredzi soils are brown sandy clay loams of medium acidity. Nitrogen status in the ploughing zone (0-30cm depth) was low, Phosphorous is available in adequate amounts, and the soils are rich in Potassium. (Table 1,2,&3). Mid term soil nutrient analysis results reveals a slight increase in available nitrogen, this is to be expected since Nitrogen fertiliser was applied as a top dressing, however there is a marked decrease in Potassium. Another soil nutrient analysis will be carried out soon after harvesting and the extent of nutrient utilisation by the crop should become apparent.

The Harare soil are brown sandy clay loams and are strongly acidic.Sorghum in general requires a soil pH range of between 5-6.5 for optimum growth (Farm Management Handbook, 1982) . It might be necessary to lime the Harare trial to moderate the acidity.Nitrogen availability status of the soil at planting was medium, but the soils showed a marked deficiency in Phosphorous but were rich in Potassium.

Table 1. Soil nutrient analysis results (for details contact Authors)

Table 2. Criteria used to determine soil nutrient levels  (for details contact Authors)

Table 3. Reccommended fertiliser rates

Fertiliser kg ha-1

Kg/ha of fertiliser nutrient required
Good Medium Poor




Up to 30 









Farm management Handbook, 1982

Pest and Disease Control:
Stalk borer (Brussela fusca) reached significant proportions which warranted spraying. The following chemicals were applied for stalk borer control: Carbaryl 85% wp, Thioflo, Thiodan 50%wp and Dipterex 2 % granular (Table 5). All the other chemicals contain endosulphan as the a.i. except for Carbaryl. Carbaryl was used mainly on the late-planted Rona H under sprinkler irrigation. Dipterex was mixed with sieved sand at a ratio of 1:2. This ensured effective chemical distribution. Endosulphan sprays were done at early stages of the borer attack and the spray was directed at plant funnels. These sprays were effective as pest levels were reduced to insignificant proportions (Table 6a & b). Spot application of Dipterex was used as a follow up application on infected plants that escaped initial chemical control. Knapsack sprayers were used for spraying.

Table 4. Pesticide application
Chemical Applied Pest Application Rate Application Date  Weeks after emergence 


Carbaryl 85%wp Leaf eaters & Stalk borer 3 – 4kg ha-1 20-12-98 1
Dipterex 2.5% ganular Stalk borer 3-4 kg ha-1 02-01-98 6

*Dimethoate 40%e.c


1.3l ha-1 

500ml ha-1




Dipterex 2.5% granular " 3-4kg ha-1 10-01-98 7 ½
Thiodan 50 % wp 


*Thiodan 50% wp

" 1kg ha-1 


1kg ha-1



01 & 23 – 01-98

8 ½ 


4 & 8

Thioflo " 1.3l ha-1  


* Harare

Table 5a. Scouting results before spraying:
Variety No. plants scouted No.plants attacked Date of scouting
Keller 12 3 18/12/97
Monori edes 12 1 18/12/97
Rona H 12 4 18/12/97
Is19674 12 3 18/12/97
Cowley 12 6 18/12/97

Table 5b. Scouting results one week after spraying:
Variety No. plants scouted No.plants attacked Date of scouting
Keller 12 1 25/12/97
Monori edes 12 0 25/12/97
Rona H 12 2 25/12/97
Is19674 12 1 25/12/97
Cowley 12 4 25/12/97

The results shows that control measures were very effective. Cowley showed high susceptibility to stem borer attack compared to the other varieties. Aphids attack was very low on the Chiredzi trial and no control measures were done on the few cases recorded.


The following diseases were noticed in the sweet sorghum crop at Chiredzi Research Station:

-leaf blight (Helminthosporium turcicum),Rust (Puccinia purpurea cooke), and Sooty stripe (Ramulispora Sorghi) None of the above cases were serious as they appeared in isolated cases. No chemicals were applied. Rouging was carried out as a control measure.

The high temperatures during the month of December and January resulted in very high evaporation readings recorded. This inreased the irrigation frequency to almost weekly, as depletion rates were very high. Irrigation was started two to three days before the net depth of application on that particular week is depleted to reduce chances of stressing the plants. However in most cases pump failure and problems associated with the switchboard (for irrigation pumps) resulted in some irrigation not being carried out (Table 5)

A total of 298mm was applied on the experimental plot on the 2.5ha of the remaining drip irrigated section (Picture 1) and the sprinkler irrigated (Picture 2) section 102mm and 234mm were applied (See Table 11).



Picture 1. Spinkler irrigated Keller

Picture 2. Aerial view of the drip irrigated crop

Biomass accumulation

Peak freshweight biomass for all varieties were recorded at or between 87 to 101 days after emergence. with Monori edes recording the highest freshweight biomass of 84 tonnes (See Table 6 & Graph 1).Keller planted in Harare exhibited similar growth characteristics to those of Keller planted in Chiredzi, but taking longer to maturity , approximately 145 days, but in terms of biomass there was no significant difference in results recorded.

Sugar analysis

Rona H was the first variety to be analysed for sugars; it reached the booting stage much earlier than the other varieties. Results on sugar analysis are shown on (Table 7). Sugar content for all varieties reached a peak at the start of the hard dough stage (Graph 2). Keller recorded the highest pol % followed by Cowley, Is19674, Monori edes, and then Rona-H. The local varieties recorded on average Pol of as low as 4%, Brix of 9% and purity of below 50%.

Triangle Sugar analysis

Sugar analysis carried out by Triangle revealed similar results with Keller and Cowley recording the highest pol % (Table 8). The alcohol yield compared favourably with that of grade C-molasses, which is used currently by Triangle, limited for ethanol extraction. (Table 9 a & b).

Table 6.Growth Analysis for First Trial. (97 / 98) (Contact Authors for this table)


Table 7. Sugar Analysis for first trial (97 / 98) (Contact Authors for this table)

Graph 1. Dry matter accumulation

Graph 2. Sugar accumulation for the 5 varieties


Table 8. Triangle sugar analysis results
Variety Brix Pol Purity %TRS %URFS %TFS



Monori edes



























Table 9 Ethanol yield
  Absolute Ethanol  Yield (ml)per Raw  Juice
Sample Yield 100g-1   

Yield TRS 100g-1


TF 100g-1

Sugarcane 1 = 50.98 55.78



Monori edes













Triangle Pvt (Limited): Courtesy Mr D. Siwela


Pol % (sucrose content) gives a guide on variety sugar content. (Bala et al, 1997) did a similar experiment where they tested several varieties for sugar content They observed that under optimum conditions and at maturity varieties with high total sugar content can have a sucrose, % as high as 13%. The results show a gradual increase in sucrose content with maturity. This trend tends to concur with the conclusion of Bala and Ratnavathi (1997) who noted that with some sweet sorghum varieties sugar accumulation pattern is such that it increases in rate up to early soft dough stage and decelerated during hard dough stage which may coincide with grain filling.

See Pictures 3.4.

The sweet sorghum crop was successfully milled (see pictures 4,5& 6.). however no further tests were possible on either juice or the fibre derived from the crushing.

Storability test
Deterioration was much faster for stems that had been harvested and stripped of leaves. It was slowest in the stems that had been stripped but left standing. (Table 11). ) This result has important implications for the manipulation of the period of industrial utilisation and strategies for short term storage. The ability to ‘store’ the crop in the field allows some ability to de-couple harvesting from mill utilisation adding some flexibility to farmers harvesting schedules.

Purnomo and Sumantri (1997) also noted that if stalks are cut, it leads to high rates of respiration and this results in post harvest losses. In view of this prompt processing is essential to avoid inversion losses of sucrose. It is also advisable to remove the leaves, this is very important in as far as purity % is concerned. Purnomo and Sumantri (1997) have reported that removing leaves and seed heads produces better quality of sugar. When it comes to harvesting the following constrains are envisaged.


i) problems when it comes to leaf stripping

ii) immediate transportation of crop for processing


Possible solutions to these problems would be to use defoliants prior to harvesting, it would also be vital to look at existing (or to develop) machinery specific to sweet sorghum for quick and efficient harvesting. Sweet Sorghum-specific harvesting machines have been developed in the 1990s through a European Union funded project and trials using large-scale sugarcane harvesters have been carried out by researchers in the USA and Australia.

To maintain a steady supply of crop to a mill, farmers may have to consider staggering planting dates, however more research would have to be carried out on the effects of planting dates on biomass and sugar accumulation for the different climates.

Table 10. Storability tests results




S & S
S & S
LEAVES -Plants were stripped off their leaves and left standing in the field.
SS - -Plants were removed from the field and stems stripped of their leaves
STEMS -Plants were removed from the field and stored with leaves

Seed bulking
It is realised that if this project goes into the third phase, in which a proposal to plant 300ha to sweet sorghum at Triangle (Pvt) Ltd has been put forward, it is estimated that 3 tonnes of seed will be required, which is a large quantity. In view of this, we reckoned that it might be a good idea to commence seed bulking, though it is the major activity in the second phase of the project. Seed bulked for Keller was from the sprinkler irrigated land (Picture 1) Grain yield estimation ranged between 2.5 to 3.5t/ha.


Picture 3. Hand harvesting of sweet sorghum stems

Picture 4. Mechanical loading of stem bundles

Picture 5. Unloading at Triangle

Picture 6. Crushing of stems

Picture 7. Sweet sorghum bagasse


The results of the first year have already highlighted two sweet sorghum varieties with good characteristics for ethanol and electricity production provided under both the conditions experienced at both trial sites. The second year will build on the first year by evaluating these two varieties further, to improve on the understanding of optimum growth conditions, and

Evaluate new germplasm, which may have better biomass quality, yields, resistance to drought and pests and diseases or combinations of all these qualities. This 2nd year trial will also evaluate the Period of Industrial Use (PIU) by carrying out a staggered planting regime and monitoring the accumulation of sugars and fibre depending on planting date and crop duration.

The results from the first year trial have allowed some interesting comparisons with sugarcane to be made. Whilst it is important to note that the sorghum will not be in competition with sugarcane, sweet sorghum must be able to achieve comparable standards in biomass productivity, quality and efficiency of resource requirements if it is to be considered as a serious possibility for ethanol and electricity production. Initial calculations from this years trial data suggest that sweet sorghum can compare very favourably with sugarcane.

For example, the projected ethanol production of 3500 l ha-1 of sorghum can be contrasted with the expected production of 7900 l ha-1 for sugarcane. However, to achieve this ethanol yield, it requires 12 months (365 days) as compared to 3-4 months (100 days) for sweet sorghum. The more revealing specific ethanol productivity shows that sweet sorghum produces 35 l per ha growing day as compared to 22 l per ha growing day for sugarcane i.e. on a daily basis sweet sorghum can produce over 50% more ethanol than sugarcane. Obviously, this will have implications on resource use efficiency. For example, accounting only for water use during crop growth, sugarcane would require 2.53 m3 of water per litre of ethanol produced (assuming all sugars from sugarcane went to fermentation and no crystalline sugar was produced). Sweet sorghum on the same basis would require only 1.77 m3 of water per litre of ethanol produced, a saving on water of over 40%.

The project is now considered to be in a highly promising state for building on the success of the first year. Sweet sorghum has been shown to have the correct characteristics for a significant new level of use helping to diversify away from sugar production and helping build a sustainable future.


AGRITEX, Crops & Horticulture in Ed. J. de Jong Part 1, FARM MANAGEMENT HANDBOOK, AGRITEX, p1-3, Harare, Zimbabwe; 1982.

Bala Ravi, S. and Ratnavathi, C.V. 1997. Pattern of drymatter accumulation and partition between panicle and stalk in grain and sweet sorghum. Proceedings, First International Sweet Sorghum Conference. (Li Dajue, ed.). 466.

Bala Ravi, S., Biswas, P.K., and Ratnavathi, C.V. 1997. Genetic variability and stability for the major traits of sweet sorghum. Proceedings, First International Sweet Sorghum Conference. (Li Dajue, ed.). 303

Purnomo E., and Sumantri A., 1997,The experiences of making sugars from Sweet Sorghum in Indonesia, . Proceedings, First International Sweet Sorghum Conference. (Li Dajue, ed.).pp 80.

 Back to top of page
 Back to Sweet Sorghum Project Main Page