Part Two

Project elements

An outline of the project's objectives, outputs and activities is given below. A fuller description of the role of each activity and their interrelationships are described in section K (The Work plan)

F. The immediate objectives of the project

1. Objective: Demonstrate the feasibility of co-cropping sweet sorghum with sugar cane on two test sites in Zimbabwe, through agronomic trials and biomass production (see Section K. Work plan)

1.1 Output: Productivity data (total above ground plant production per hectare)

1.1.1 Activity: Mass measurements (fresh and dry weight) to be carried out during agronomic trials planted at Triangle / Chiredzi, year 1(research station), year 2 (fallow), and year 3 (fallow) trials

1.1.2 Activity: as above (1.1.1) based at SIRDC Research Centre, Harare, year 1, 2 trials

1.2 Output: Partitioning data (fibre, sugars, stems, tops & leaves, & roots)

1.2.1 Activity: Partitioning protocol to be carried out as 1.1.1 above

1.2.2 Activity: Partitioning protocol carried out as 1.1.2 above

1.3 Output: Resource use data (monitoring of water, fertilizers, pesticides, energy & labour) at each location.

1.3.1 Activity Resource use protocol to be carried out as 1.1.1 above

1.3.2 Activity Resource use protocol to be carried out as 1.1.2 above

1.4 Output: Sweet Sorghum biomass

1.4.1 Activity: Triangle, year 3 trial to produce sufficient biomass on 300 ha (fallow) for crushing and conversion to electricity, heat, and ethanol at Triangle Sugar Mill.

2. Objective: Demonstrate the economic and technical viability of utilising sweet sorghum within an existing sugar mill for energy production through:

2.1 Output Juice extraction (Processing of biomass)

2.1.1 Activity: Harvest & transport, storage

2.1.2 Activity: Crushing / diffusion (Juice extraction)

2.1.3 Activity: Data collection and analysis

2.2. Output: Energy production (Conversion)

2.2.1 Activity: Combustion / steam turbines for electricity & process steam production

2.2.2 Activity: Fermentation for ethanol production

2.2.3 Activity: Data collection and analysis

3. Objective: Development of a Systems Analysis Model (AIP- Agrosystems Integration Package) and decision support system to assess the replicability of the co-cropping system elsewhere and to allow the impact of novel technologies and management practices to be assessed throughout the complete energy chain in order to minimise economic and technical risk.

3.1 Output: Systems Analysis Model for decision support

3.1.1 Activity: Data collation and analysis

3.1.2 Activity: Database development and data input

3.1.3 Activity: Model development (programming)

3.2 Output: Model Validation

3.2.1 Activity: Model runs and sensitivity analysis

4. Objective: Disseminate the project outputs.

4.1 Output: Workshop

4.1.1 Activity: Carry out a 2 week workshop with 30 participants from Southern Africa and other regions

4.1.2 Activity: Produce Workshop Manual

4.2 Output: Mid-term Assessment

4.2.1 Activity: Assess and report success of year 1 & 2 agronomic trials and approve the implementation of phase II.

4.3 Output: Technological dissemination

4.3.1 Activity: Technical exchange visits will be carried out through visiting technicians / agronomists observing the project during critical project periods.

4.4 Output: Reports

4.4.1 Activity: Progress reports

4.4.2 Activity: Annual assessments

G. The scientific or technical problems to be addressed and the feasibility of the proposed project

Triangle Ltd. Zimbabwe has been running a 40 Ml per year ethanol fermentation plant for the production of fuel alcohol (Ethanol) for the last 16 years to supply the internal gasoline market with blended fuel. This plant was originally constructed to address problems of energy security with economic considerations of secondary importance. More recently, the combination of a strong global sugar market and relatively cheap supplies of petroleum have enhanced the value of crystalline sugar relative to fuel ethanol. Therefore, Triangle Ltd. has reconfigured it's plant to maximise crystalline sugar production from sugarcane at the expense of ethanol production. However, there is also a strong international market for ethanol mainly driven by environmental requirements of ethanol as a fuel oxygenate in the United States and Europe and as a petroleum substitute in Brazil. (see attachment 2)

Furthermore, for economic and environmental reasons, research is now being carried out with the aim of increasing energy production (electricity and heat) from sugarcane mills through the integration of novel biomass conversion technologies and high efficiency steam utilisation technologies. (for example see Gabra, & Kjellström, 1995; and Larson, & Hughes, 1996) In fact, within 5 year's, sugar mills could increase their electricity production at least 10 fold simply by utilising cane residues more efficiently. There are many potential advantages to such economic, rurally-based bioenergy systems including sustainable development, increased food production and improved health for rural populations who have access to clean fuels for lighting and cooking if such systems are adopted. {Woods & Hall, 1994; Hall et al, 1993; IPCC, 1996; Johansson et al, 1996}

The technical challenge is to reduce ethanol production costs whilst increasing production without affecting crystalline sugar production in a way which is applicable to other sugar producing regions. Simultaneously, significant increases in electricity and process energy are possible and a significant extension to the energy production season by the mill can result- this is an important economic consideration for the company and the region. (For economic discussion see section H.) Before such a novel ethanol, heat and electricity producing system could be regarded as acceptable, it will have to demonstrate:

Through intensive agronomic research over the last decade in the USA, Australia, Brazil and Europe - see table 1 - sweet sorghum has emerged as a viable feedstock for fuel ethanol production. The potential for utilising sweet sorghum is based on a combination of advantageous agronomic characteristics. It has one of the highest intercepted radiation use efficiencies of any plant species, on a par with sugarcane, so allowing it to grow rapidly under optimal conditions. However, it's real potential lies in its growth under sub-optimal conditions where it combines high light use efficiency with high water and nutrient use efficiency, whilst continuing to produce a sugar and fibre rich stem. {Woods et al, 1995; Gosse et al, 1995; Muchow & Coates, 1986} This robustness is the main reason that sorghum has been the crop of choice for farmers in drought prone regions as it requires low water and nitrogen (fertiliser) inputs and is tolerant to drought stress.

Under good conditions sweet sorghum varieties can outperform sugarcane in terms of total biomass production over short periods; however, problems persist with sucrose purity which rule out sweet sorghum as a candidate for commercial crystalline sugar production. Sweet sorghum's rapid growth and ability to reach maturity in 3 to 5 months are favourable to its production on fallow sugarcane land for harvesting before the start of the sugarcane harvesting season. Higher yielding varieties have now been developed, capable of producing well over 100 fresh weight tonnes of above ground biomass in 5 months under good agronomic conditions where water, nutrients and pests are fully controlled. Furthermore, sorghum biomass takes less water to produce than sugarcane, significantly reducing the amount of water required per litre of ethanol produced compared to sugarcane derived ethanol. {Woods et al 1996; Roman et al, 1995}

Since sweet sorghum has not yet been grown so that it can be integrated with sugarcane growth schedules, it will be necessary to assess the impact of sweet sorghum on sugarcane productivity. Potential problems resulting from a crop rotation system which uses a C4 crop following C4 crop, such as the build up of pests

Table 1: Main Developments and Projects in Sorghum Research (1970 to present)
Duration Region Co-coordinator Project Title
1995-96 European Union D.O. Hall 


APAS Project:"The Production of Electricity & Biofuels Through the Integration of Sweet Sorghum into the Sugar Industry in Developing Countries". 
1992-95 European Union D.O. Hall 


JOULE II Project: "Bioethanol Production from Sweet Sorghum: interchange of research and experience between EC and developing countries (Zimbabwe and Thailand) 
1992-95 European Union G. Gosse 


AIR Concerted Action: 

"Sorghum, A crop for Industry and Energy Supply" 

1985-92 France G. Gosse 


INRA "Sweet Sorghum Productivity & Modelling" 
1980s (still continuing) USA Vanderlip 


Kansas State University 

"Development of SORKAM model" 

University of Hawaii (and others) 

"Development of Sorghum CERES model" 

1970's USA Arkin 

(TA & M) 

Texas A&M 

"Development of SORGF model"

and diseases, which will only be seen in a full scale trial and continuous production over a number of years. (see section M- "Risk") However, research has been carried out, directly intercropping maize with sugarcane, and suggests that such problems can be overcome with good management. Such management would ensure that in an intercopping system competition for nutrients and water between the two crops is minimised mainly by ensuring that applications are sufficient in quantity and timing. {Wallace et al;, 1991}

Modelling, Replication and Advanced Technologies

Whilst a biomass energy project may be successful in one location, problems can be encountered when replicating such a project in another location. Historically, policy makers and entrepreneurs have sometimes failed to recognise the complexities involved with bioenergy schemes which are often critically dependant on site specific factors such as:

In order to assess the impact of these variables at separate locations, or the impact of new technologies in the same location, a systems analysis approach is necessary. Systems Analysis typically involves data intensive computer based modelling. In the Agrosystems Integration Package (AIP) under development at King's College London, process-driven crop models are being used which are able to account for the variability in site specific productivity, and individual modules describe each step of an entire energy chain ie. from biomass growth to final processing and conversion to energy (electricity, heat, power, ethanol), in order to assess the impact of changes in any of the other variables listed above.(see attachment 6, and, Tsuji et al., 1994) Thus, the potential influence of soils, or climate, can be assessed in terms of productivity and economic return. Importantly, it will be possible to carry out sensitivity analyses for all the factors listed above using the AIP. The AIP will provide a user friendly decision support system to enable managers and technicians / agronomists to assess the viability of this sorghum system elsewhere.

In the proposed system which integrates sweet sorghum with sugarcane an extra level of complexity is added to existing monocropping systems ie. sugarcane only. In order to optimise the integration of sweet sorghum into the sugarcane agronomic and milling schedules, in addition to the factors listed above, temporal factors need to be assessed, for example, the timing of the availability of fallow land for the planting of sweet sorghum, and the period of availability of the mill during harvesting. In such complex systems, a systems analysis approach is critical in order to integrate the impacts of changes at each level, to provide realistic estimates of costs, environmental impacts and microeconomics. {Tsuji et al., 1994}

It is now evident that in order to realise the potential of Sweet Sorghum for energy production as a commercially viable system it is now necessary to demonstrate a sorghum to ethanol and electricity system within an existing facility.

Potential Land Availability

Sugarcane is grown in southern Zimbabwe on a 12 month growth cycle with old unproductive ratoons removed after 10 years (10 cropping cycles). Therefore, it might be expected in any one year that 10% of the land under sugarcane would be left fallow and therefore available for sorghum growth. However, for reasons explained below only about half of this fallow land can be considered for sorghum growth.

At Triangle, harvesting starts at the beginning of April and continues through to the end of November and the beginning of December when all harvesting stops and the mill is closed down. The mill therefore runs for a 9 month season and is closed for maintenance for three months. Once old sugarcane ratoons are removed, the land is ploughed and left fallow for three months, or an alternative crop is planted, such as cotton. However, because of the 12 month growth cycle, and the need to leave the land unplanted for at least three months, land under 10 year old ratoons harvested less than 3 months before the end of the harvesting season is left for replanting until the beginning of the next season. It is this land, which will be left fallow for a minimum of 5 months (the "off crop"), which provides the best opportunity for sweet sorghum growth for ethanol production. {Woods et al., 1996}

In a simple co-cropping system, where sorghum would be planted immediately after the old sugarcane ratoons have been removed, up to 5% of the total land under sugarcane could be used for sorghum growth. For the Triangle Estates, this represents 690 ha capable of producing over 2 million litres of ethanol per year.

A clear advantage of the proposed co-cropping system is that there is a synergy between the timing of the availability of this fallow land and the optimum period for sweet sorghum growth. The end of the harvesting season in November / December coincides with the start of the rainy season in Zimbabwe when rainfall, solar radiation and temperatures are at their highest. These conditions are optimal for the growth of sweet sorghum given good agricultural management. This is also true for the sugarcane crop which assimilates a significant proportion of its final Carbon stock during these critical growth months. Therefore, if intercropping of sweet sorghum with sugarcane occurred this could lead to significant competition between the two crops and a reduction in net crystalline sugar production per year. Thus, sweet sorghum will be grown using fallow land in a co-cropping system, and intercropping will not be considered.

The systems analysis modelling will provide a practical tool for calculating resource requirements (that is: variety selection, planting times, optimum harvesting period, equipment and personnel requirements), for a given level of ethanol and electricity production (see Attachment 6).

Future expansion of land for sweet sorghum production

As a result of sorghum's tolerance to environmental stress, it is widely grown throughout Africa in drought prone regions. For this reason it is grown by many poor farmers in Africa, central and south America. Whilst there is the potential to produce significant amounts of additional ethanol from sweet sorghum on existing fallow sugarcane land, the potential for wider expansion through the growth of sweet sorghum by small scale farmers as a cash crop should be explored. However, transport distances from the point of harvest to the mill are critical for economic production of ethanol. Therefore, alternatives to the agroindustrial system proposed above will be analysed. For example, on-site crushing will considerably reduce the mass of material to be transported to the mill, but may be offset by the cost of small scale mobile crushing equipment.

We consider it unlikely that intercropping (as opposed to co-cropping proposed in this proposal) will be adopted to increase ethanol and electricity production when the maximum amount of fallow land has been utilised. We believe that further expansion of sweet sorghum production for ethanol and electricity production will be based on small scale commercial farmers, and more importantly on communal farmers, who already grow sorghum for beer and seed production. Thus, sweet sorghum could represent a significant cash crop to communal farmers, who currently rely on maize, which has been prone to drought and disease failure over the last 10 years. Importantly, a number of communal farmers already produce grain sorghum which is sold to Triangle Ltd for cattle fodder.

H. Economic and financial justification

Profitability of Ethanol from Sugarcane Molasses in Zimbabwe

The profitability of the ethanol operation at Triangle is very much dependant on the price of raw materials, namely molasses. Prior to the commissioning of the plant, there was a vast excess of this commodity in Zimbabwe. With demand for molasses now being established, the price has risen steadily over the past 5 years. As with any commodity, different markets are prepared to pay a different price for molasses, and the Triangle ethanol plant is now considered the buyer of last resort. It is however, a guaranteed consumer of molasses. At the beginning of each year, Triangle declares a price that it si prepared to pay for molasses up until the start of the season. This price is generally based on an export parity price for world market sales of molasses, and includes the cost of transport, handling and port storage. For the current year, this price is ZW$170.00 per tonne.

A breakdown of this years costs for the ethanol operation are as follows:
Item ZW$
Plant maintenance costs 1,071,000
Plant Operational costs 659,000
Chemicals 638,000
Steam 3,524,000
Electricity 762,000
Administration (Management, Insurance, Depreciation) 3,400,000
Raw Materials 14,685,000
TOTAL 24,739,000

Based on nineteen million litres of ethanol production, (requiring 78,000 tonnes of molasses), revenue is expected to reach $37,819,000. This equates to around US cents 29/litre. These costs equate to around US cents 15.3 per litre.

Estimated Costs of Ethanol Production from Sweet Sorghum

Depending on assumptions made regarding sweet sorghum productivity, biomass yield, ethanol yields and agronomic input costs, the cost of ethanol from sweet sorghum varies between 15 to 40 US cents per litre under Zimbabwean conditions. Current ethanol production costs from sugarcane molasses at Triangle Ltd. are about 20 US cents per litre, which can be compared with a US export price for ethanol of 35.6 - 36.9 US cents per litre. Much of this ethanol is used in gasoline/ethanol blends, where the ethanol is used as an oxygenate.

Estimated costs for ethanol production from sweet sorghum, utilising the existing Triangle facilities, and assuming similar costs for processing to sugarcane, are given in table 2. These ethanol costs are based on data gained from the earlier sweet sorghum trials in Zimbabwe and on the production costs of Triangle's commercial sugarcane to ethanol system.

Ethanol production costs are broken down into agronomic and conversion costs, and potential revenue is estimated from the present internal (Zimbabwe) value for fuel ethanol (19 US cents per litre). These costs are based directly on Triangle Ltd's sugarcane agronomic production, transportation and processing costs. Agronomic costs provide total costs for all inputs, harvesting and transport. Raw material storage costs are excluded because sugar levels in sweet sorghum are sensitive to storage and rapid processing is required after harvesting. Irrigation costs based on the assumption that 400 mm rainfall occurs during the summer (off crop) season. Conversion costs include the fixed and variable costs associated with ethanol production at Triangle's facilities. Depreciation costs on machinery and equipment are not included as these costs will initially be written off against sugarcane production and conversion. Since the sweet sorghum-based ethanol and electricity production will utilise existing sugarcane equipment which will be idle during the sweet sorghum harvesting and conversion period, the capital costs of this equipment is not included.

High, mean and low cost estimates generated from the trial data are provided based on one standard deviation, above and below the mean. Where sufficient data was not available a ± 20% deviation was used. The mean transportation distance observed for sugarcane at Triangle Ltd. of 20km was used to derive feedstock transportation costs. A more comprehensive analysis of transportation costs in relation to the optimum size for a bioenergy conversion plant for the production of ethanol from sugarcane and sweet sorghum can be obtained from Nguyen and Prince, 1996. However, it should be noted that crop production costs increase with plant size, mainly as a function of increased average transport distances, but factory conversion costs decrease with increasing plant size as a function of scale up cost reductions.

The data in this table should be considered as conservative, representing the average current sweet sorghum data for Zimbabwe. Undoubtedly, only the best varieties would be utilised in commercial production which would be selected for their high yield and water use efficiency. These varieties also exhibit good sugar and fibre qualities.

It is interesting to note that varieties in European trials have produced significantly higher yields- 110 fresh weight tonnes per hectare per growth cycle; {Roman et al, 1995}- than trials so far conducted in Zimbabwe. Yields of 77 fresh weight tonnes per hectare have been achieved in agronomic trials in southern Zimbabwe, which we consider still to be below the maximum potential for sweet sorghum. However, climatic and soil conditions are very favourable in Southern Zimbabwe and yields greater than 100 tonnes per hectare may well be attainable in the future. It is significant that this region of Zimbabwe has produced the world's highest average sugarcane yields over the last 15 years, and continues to produce at these levels (except in the 1992/3 drought year). {Woods & Hall, 1994; FAO, 1994 Production Year Book.}

We therefore consider that considerable improvements are possible in the economics of sweet sorghum to ethanol production, when compared to the costs shown in table 2. Successful ethanol production from sweet sorghum is dependent on good integration with sugarcane production, thereby optimising the use of equipment and resources during a period in which they would otherwise be unused.

Profitability of Ethanol from Sweet Sorghum

The estimated mean and low costs (14.4- 17.4 US cents respectively) for ethanol production from sweet sorghum would be competitive with current US gasoline prices (around US cents 20 per litre); however this estimate is a production cost and not a delivered cost estimate. Importantly, this estimated ethanol production cost is cheaper than the imported cost of gasoline into Zimbabwe. Ethanol used as an oxygenate in gasoline formulations attracts a much higher value (litre for litre) and has traded in world markets in 1996 at around US cents 35 per litre. As noted in Attachment 2 (World Ethanol Market), prices for ethanol as an oxygenate are expected to decline over the next few years to around US cents 28 per litre. At this price, ethanol from sweet sorghum would remain profitable.

Table 2: Draft Estimated Costs of Ethanol production from Sweet Sorghum Utilising all Facilities at Triangle Ltd, Lowveld, Zimbabwe 
Unless stated t = fresh weight tonne (approx 75% moisture, wet basis)
Total Feedstock Production  tonnes (FW) 15000 
Ethanol Value§ Z$/litre 1.60 
Coal Value Z$/tonne 350 
Units Mean Low High
Sorghum Productivity tonnes/ha 50  30  80 
Land Required ha 300  188  500 
OUTPUTS Units Mean Low High
Ethanol Value (Gross) Z$ 977000 557000 1509000
Ethanol Production litre 610805  348423  943297 
Bagasse Prodn. (50% m/c) tonnes 2257  1814  2701 
INPUTS Units Mean Low High
Agronomic Z$/ha 2550  2009  4606 
Z$/litre 1.252  1.081  2.441 
Water Requirements M litres 1355  789  1921 
If rain.... 'mm' then million l reqd. ->


39  155 
Cost Z$ 35232  139715 
water cost per litre Ethanol

Z$ / litre Ethanol

0.058 0.000 0.148
Steam Z$/litre 0.03  0.66 
Fermentation Z$/litre 0.14  0.14  0.14 
Production Cost per litre Z$/litre 1.48  1.22  3.39 
Total Cost Z$ 903797 425425  3196941 
Balance Z$ 73203  -1687941  131575 
Ethanol Production Costs


0.174  0.144  0.399 

Note: M=million (106) m/c = moisture content

§ Price received by Triangle Limited under Zimbabwe Government Contract, set to gasoline import price.

"Mean, Low and High" are always respected for each row of the table. For example the "Low" ethanol production cost is the lowest possible production cost, resulting from a combination of high productivity and low production and conversion costs, and represents a "best possible case scenario" (under the assumptions used here)

Zimbabwe $ 8.5 per US$ (1996)

¶ Agronomic costs derived from blanket cost for sugarcane land preparation, growth, harvesting and transport at Triangle Ltd.

I. Social Impact

Extending the harvesting and milling season will reduce the seasonality of employment in field and factory. Seasonality is seen as an inherent social problem in strongly agricultural economies resulting in a significant proportion of the labour force being unemployed during the yearly growth cycles. Often, in developing countries this labour is required by the commercial agricultural sector at the time when their labour would also be most useful on communal land holding. In a dual crop system, as proposed here, which extends the growing, harvesting and milling seasons, seasonality in employment is reduced, thereby raising the income of this sector of the regional workforce.

At the same time, increases in rural income are achieved by providing an extra cash crop (sweet sorghum) for small scale commercial and communal farmers who would provide the main feedstock for expansion of ethanol and electricity production from Sweet Sorghum, before the sugarcane season begins.

These benefits will impact across a broad section of the population, listed below:

(a) Rural workers;

(b) Factory workers;

(c) Communal farmers;

(d) Commercial cane growers; and

(e) The broader population through a lower level of polluting emissions when ethanol produced from sweet sorghum is used as a fuel oxygenate.

Biomass energy systems can provide a labour intensive and cost effective means of employment generation in rural regions, as discussed below.

Employment Potential. {Woods & Hall, 1994; Johansson et al, 1995}

The history of agricultural development is often characterised by the reduction in man hours per tonne of produce harvested. The fall in manpower required in agriculture has accentuated, or is a direct cause of urban drift so exacerbating urban unemployment and related problems.

One trait of agriculture is the seasonality of the employment. In developing countries where the bulk of the harvest is often carried out manually this requirement for large numbers of temporary jobs during the harvesting season is regarded as socially damaging. Whilst the quality of the work may be poor it does at least provide some form of income where there might not otherwise be any. It should therefore not be the aim of any investment programme to destroy this important opportunity for income. Rather the aim should be to secure those jobs throughout the year in the most economically efficient way, possibly by providing alternative employment during the off-season.

The Carpentieri et al. (1993) study of biomass electricity in NE Brazil provided a detailed analysis of the manpower requirements for both the tree plantation and sugarcane biomass energy sectors and serves as a useful illustration for the employment potential of this bioenergy producing system. The sugarcane industry of this Brazilian region presently employs labour at the rate of 19.8 jobs per km2 for on-season work and only 2.7 jobs per km2 for off-season (permanent) employment. If in the future labour was to be employed to bale and collect the tops & leaves which would be done off-season (an essential activity if enough energy is to be produced from sugarcane residues), then the on-season requirement for jobs would not change at 19.6 jobs km-2 but the off-season requirement would rise to 23.7 jobs km-2 . At present only about 36,000 people are employed permanently by the sugarcane industry of the NE region. However, if the industry became a combined sugar and energy production system the theoretical total number of permanent jobs is estimated to be more than 326,000. The seasonal requirement (harvesting period only) would fall from 272,600 to 55,800 people, with all the present seasonal jobs being absorbed into the extra permanent vacancies. The introduction of sweet sorghum into such a system would also increase the potential employment benefit.

In the agro-ethanol industry, job quality is also comparable or higher to many of the main large-scale agricultural employers in Brazil. It is estimated that the ethanol industry in Brazil has generated 700,000 jobs with a relatively low seasonal component compared to other agricultural employment. Job security and wages are important for workers in this industry.

An important developmental comparison is the investment cost per job created. For the biomass energy industries in Brazil this lies between US$15,000 and $100,000 per job, with costs in the ethanol agro-industry between US$12,000 and US$22,000. Such job creation costs compare with the average employment costs in industrial projects in NE Brazil at $40,000 per job created, in the petro-chemical industry of about US$800,000 per job, and for hydro power over US$106 per job. Lower job creation costs are one of the most significant benefits of biomass energy.{Carpentieri et al., 1993; Goldemberg et al., 1992}.

J. Environmental Impact

Environmental issues are considered significant at present. Two perspectives are relevant to this project: first, there is likely to be a net positive environmental impact of sweet sorghum production at a regional level; and second, the use of sweet sorghum as a biofuel avoids the use of fossil-fuels which emit greenhouse gases.

(a) Net environmental benefits

An examination of the resource requirements for sweet sorghum production is provided in attachment 7 - Hall & Woods, 1996. Environmental issues are divided into nutrient fluxes, resource use efficiency, water and energy ratios . The key conclusion of this environmental review is that well managed sorghum production for energy can provide net environmental benefits at the regional level. Careful monitoring is required to ensure that sorghum production does not adversely affect the local environment and that its growth is sustainable. However, with the correct management, any negative environmental impacts can be minimised and positive benefits can be gained where sweet sorghum is grown as a buffer crop between arable crops (in this case sugarcane) and water courses as a nitrogen filter crop. Importantly, the AIP could be used to evaluate the environmental impacts of sweet sorghum as an energy crop, by providing energy and nutrient balances.

(b) Climate Change

Biofuels provide an opportunity for the provision of the modern fuels and services required for development, whilst at the same time avoiding fossil-fuel derived CO2 emissions, thereby drawing down atmospheric levels of CO2 . However, present intensive agricultural methods should only be used for the production of liquid fuels, eg. ethanol from sugarcane or maize, diesel from rapeseed, if the associated residues are used for energy. Thus the use of C-flows and energy output:input ratios to monitor net CO2 production must be integral to the study of the Greenhouse effect and the development of strategies for energy provision.

Bioenergy systems emit less sulphur dioxide (since they are naturally low in S) and nitrous oxides (NOx) emissions can be less than equivalent fossil-fuel derived energy. SO2 emissions are implicated in acid rain and increased nutrient depletion from soils. On the other hand, sulphate aerosols, derived from SO2 emissions to the atmosphere are postulated to moderate the global warming effect. The precise effects are still being examined. { Intergovernmental Panel on Climate Change (IPCC), 1996; Woods & Hall, 1994}

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