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Sweet Sorghum : an alternative energy crop

Final Report Summary - SWEETFUEL (Sweet Sorghum : an alternative energy crop)

Executive Summary:
1. Executive Summary
Fossil resources are limited while world energy demand is expected to greatly increase in the next years, especially from China and India. On the other hand, it is tremendously urgent to tackle climate change through mitigation of GHG released in the atmosphere particularly the CO2 resulting from the use of fossil fuel in transport
Bioethanol is considered today as a valid subsitute to fossil fuels. The current crops used to produce bioethanol are sugarcane under tropical area and corn under temperate climate. SWEETFUEL project proposed to study an alternative energy crop : sorghum. This plant can produce high biomass yield and thus could be used for 2nd generation ethanol (or biogas) production under temperate zone, and as some "sweet " varieties can accumulate sugar in their stalks while producing grain in their panicles, they can also be used to produce 1st generation ethanol from their stalks whitout totally compromising food security under tropical area.
As the main bottleneck for ethanol development from sorghum seemed to be the lack of plant material adpated to the target environments, three breeding programmes were developed in the frame of SWEETFUEL. Taking into account the process of transformation, the first programme targeted a biomass sorghum better adaptated to low temperature suitable for temperate zone and 2G ethanol production, while the two others focussed on a sweet sorghum better tolerant to drought and/or low fertility environments under semi-arid tropical climat, and suitable for 1G ethanol production.
Beside the breeding effort, activities on plant functioning were conducted to identify useful traits for sweet sorghum sugar production and adaptation to drought, and characterize their physiological and genetic bases. Particular attention was paid to evaluate in terms of carbon allocation, the competition between grain filling and sugar accumulation in stalk of sweet sorghum. Based on the data, a structure-function model was developed.
A work progamme was also developed to understand the agronomic determinants of optimized yield to recommand the best cultural and harvest techniques. A crop model was developed for exploring effect of climate change as well as cultural practices on the crop, and identifying target population of environments.
Finally a complete multicriteria evaluation of the sustainability of the sweet and biomass sorghum production uses and routes was completed taking into account technological, environmental, economic and social aspects.

All results were actively disseminated through project website as well as a Project Newsletter, many scientific publications, oral and poster presentations at international conferences and press releases.

Project Context and Objectives:
2. Project Context and Main Objectives
Fossil resources are limited while world energy demand is expected to greatly increase in the next years, especially from China and India. This will result in rising oil prices and prohibit extensive use of this resource in the future. On the other hand, it is tremendously urgent to tackle climate change through mitigation of GHG released in the atmosphere. CO2 from the use of fossil fuel in transport sector is the main component of the GHG : in Europe, it could represent 60% of the GHG emitted during the 2005-2020 period. The limits of fossil resources added to the necessity to reduce CGC emission lead many governments particularly in Europe to promote the use of biofuels in transport , .
Bioethanol is considered today as a valid subsitute to fossil fuels. First generation ethanol (1G) can be produced from sugars (sugarcane in Brazil, sugar beet in Europe) or starch (wheat or corn in USA), while second generation ethanol (2G) can be produced from any cellulosic material. Whether bioethanol represents a viable alternative to oil depends on the raw material that is used, the process of transformation and the location of production. Production from sugar cane in Brazil has a positive energy balance and allows great GHG savings, but starch ethanol from corn in USA has less positive balance and may have great negative impact on food security. 2G ethanol should have a much better energy balance and GHG savings without competing directly with food, but this technology is not yet available on the market.
Meanwhile 1G ethanol production must be developed particularly through prospection of new energy crops more efficient than maize in the temperate zone and suitable for marginal lands where sugarcane fails in the tropics.
Sorghum is one of the most efficient crops that convert atmospheric CO2 into sugar, with great advantages compared to sugarcane in the tropics and maize in the temperate zone : its cycle is short (few months), the crop can be established from seed, the production can be completely mechanized, it can accumulate sugar in stalks and produce grain, it has a high water and nutrient use efficiency, the bagasse produced from sweet sorghum has a high value (as fodder or as fuel in cogeneration) and it has a wide adaptability to environment. Finally, unlike sugarcane and maize, sorghum has a rather short breeding history, meaning that the potential of improvement through genetic enhancement is very high. All these characteristics making it a promising feedstock for bioenergy production while meeting food and fodder needs.
The Sweetfuel project was granted in the 7th Framework programme Call KBBE- 2008-3-1-02 : Sweet sorghum – An alternative energy crop for biofuel production in semi-arid and temperate regions – SICA (Latin America, South Africa, India).
The main objective was to develop ethanol production from sorghum through genetic improvement/selection of new material better adapted to the target regions. Besides breeding for biomass yield and relevant traits, the project also addressed agronomic practices and harvest technologies, as well as environmental and economic analysis including energy balance and life cycle assessment.
Sweetfuel breeding strategy was defined by taking into account first the two target zones and second the use of the biomass. In temperate regions like Europe, availability of 2G ethanol technology was anticipated and a "biomass" sorghum with a better tolerance to low temperature and lodging added with a low lignin content is targeted. Such material is also suitable for biogas production, which is already well developed in some countries like Germany. Under semi-arid climate, the target ideotype was a "sweet" sorghum, with characteristics differing according to the use of biomass. For example the ideotype targeted by EMBRAPA in Brazil, which must meet expectations of the sugarcane industrial sector was different from those targeted in India, where many smallholders are concerned and the food security issue is essential. In that case, we targeted a dual purpose sweet sorghum combining grain production and sugar accumulation in the stalks. Table 1 summarizes the ideotype characteristics of the three breeding work packages of SWEETFUEL.


The breeding effort is supported by two work packages. One aims at improving our knowledge on the accumulation of sugars (trade offs between grain production and sugar accumulation, key enzymes…) and the relationship among traits for sugar accumulation, plant phenology, stay green and drought tolerance. It is planed also to develop a model for exploring new ideotypes combining different traits in different environments. The other WP aims at better understanding agonomic determinants of optimized yield to recommand the best cultural and harvest techniques.

Finally, the complete sustainability of the sweet sorghum production and use routes is studied taking into account technological, environmental, economic and social aspects.

Attention is given to disseminate the results achieved by the different teams involved in the work plan.

General organization of the work programme is summarized in Figure 1.
Ten partners coming from seven countries and four continents were involved in the project (Table 2) to achieve the different tasks and goals through a multidisciplinary approach.
One external consultant specialist of ethical issues was involved in the consortium at the beginning of the project on the request of the Commission.

Project Results:
3. Main Scientific and Technological Results

Most of the results are reported in a one page flyer which includes a short description/explanation of the result, exploitation strategy, IPR considerations, further research and the impact of its exploitation.
Fourty one flyers were elaborated by SWEETFUEL consortium and are available from the project website (www.sweetfuel-project.eu).


3.1. IMPORTANCE OF THE CROPPING SYCLES

• The good complementarity between sugarcane and sweet sorghum
Sweetfuel through its breeding for low fertility environment programme allowed EMBRAPA to reinitiate its Energy sorghum breeding and improvement programme. It resulted in a clear identification of the expectations from the sugarcane sector, which is the major niche for sweet sorghum in Brazil today, particularly with sugarcane renovation, which is recommended to occur every five years. During sugarcane renovation, a legume crop (peanut, bean…) is frequently planted. The idea is to substitute this legume crop cycle with sweet sorghum, because harvest of sweet sorghum occurs during the sugarcane off-season. By doing this, the sugarcane sector can expect to increase its ethanol production without any additional investment for new equipment as the sweet sorghum stalks are harvested and processed like sugarcane, nor extension of exploited lands, as sorghum is planted between two sugarcane cycles. In addition, plant owners could easily extend the operating window of their plants up to 60 days (see figure 2). This excellent fit between the two crop cycles is the main driving factor, which will lead to the development of sweet sorghum in Brazil (see photos 1 to 6).
This approach can can be deployed to develop sweet sorghum ethanol value chain in other regions where a sugar industry already exists (e.g. India, North Argentina, Haïti…).

• Summer cropping or double cropping system in Europe
Due to the low temperature constraint in temperate zone, biomass sorghum is usually planted as a summer crop, which means planting in April/May for a harvest period in September/October (Figure 3). During this 4-5 months cycle, farmers can expect a biomass yield of 30 to 40 t ha-1 of dry matter.
But there is another option, which is to plant sorghum just after a winter crop for a double cropping and harvest it by September/October (Figure 3). In that case, expected biomass production is less (20 to 25 t ha-1) but this option presents the advantage of incre asing land values with a second harvest per year which allows to combine a food production with a fuel production thus decreasing a potential competition of food vs fuel.
The breeding in SWEETFUEL considered these two targets, added with a third option, which is to produce ethanol from first generation processes.


3.2. PLANT MATERIAL

As the core of the project was a breeding effort, new biomass or sweet sorghum material was produced by SWEETFUEL. This material is better adapted to the target environments taking into account the final uses of the raw material. The breeding programme is a continuous process, and even if SWEETFUEL already proposes new cultivars, we expect that better ones will be released in the near future, particularly in Brazil, India and Mexico. Information on the different biomass and sweet sorghum is included in the different flyers produced by the project than can be downloaded from: http://www.sweetfuel-project.eu/exploitable_results.

• In Brazil
EMBRAPA has registered and released three sweet sorghum varieties (BRS 508, BRS 509 and BRS 511) in 2012. This material, suitable for 1G ethanol production through the complementation of sugarcane production, meets industrial minimum requirements in terms of length of period of industrial utilization (PIU > 30days), total sugar in the juice (>12.5%) and total sugar extracted (80kg t-1). (Figure 4).
EMBRAPA planned to release 3 additional sweet varieties in 2014 and 2 to 4 sweet sorghum hybrids on 2016 and 2017, which will reach higher ethanol production per hectare.
One biomass sorghum hybrid (CMSXS7015) able to produce a good feedstock to burn for electricity production is also available for plant only dedicated to generate electricity. This photosensitive hybrid can produce up to 50-60 tons of dry biomass per ha.

These breeding materials developed and released herein are available for licensing by the private sector for seed production and commercialization.


• In India
The different improved (dual purpose) sweet sorghum combining grain and sugar accumulation in stalks, available from ICRISAT are reported in Table 3. Some of these genotypes could be tested in other countries (Brazil, Mexico, South Africa, USA, Philippines, China…) for local adaptation. The stalks or the bagasse collected after juice extraction represents a good fodder for cattle, which lead farmers to easily adopt the new material even if their main purpose is not to produce ethanol or syrup, but rather grain and fodder (Table 3).
Some genotypes were tested during the last cropping season with the sugarcane sector, and based on the first results and discussion with plant owners, sweet sorghum could easily complement sugarcane like in Brazil. Nevertheless in that case, the production of grain would remain essential as a big plant is fed by many small farmers who definitively need the grain production for their own consumption. Similarly, about 12 female hybrid parents (ICSSB 14001-14012) with over 15% Brix were developed at ICRISAT for use in heterosis breeding. Brown midrib allele introgression to the locally adapted sweet sorghum cultivars is in advanced stage which have implications in dairy and lignocellulosic biofuel production.

This SWEETFUEL exploitable result are freely available and the breeding material developed is available freely to SWEETFUEL partners and public sector partners, while private partners can avail the material by becoming members of hybrid parents research consortium and complying of appropriate Material Transfer Agreements.

• In South Africa
Through different evaluations of the ARC-GCI germplasm and exotic material collected from the consortium, ARC identified one Open Pollinated Variety, OPV007 (Figure 5) as a very good producer of sugar and fodder, as well as top 5 cultivars regarding biomass, syrup yields and sugar contents. Some of these cultivars showed also a good tolerance to mid-season and/or terminal drought stress (i.e. SSP081 and Hunnigreen).
OPV007 showed also a good potential in India and Mexico.

This material is available from ARC-GCI through a Material Transfer Agreement.

• In Mexico
UANL submitted height genotypes for registration in the national catalogue (Table 4). This material includes parental lines for new sweet sorghum hybrids as well as hybrids suitable for ethanol production. It should be soon available at commercial level.

Patent application was initiated at Servicio Nacional de Inspeccion y Certificacion de Semillas (SNICS, the Mexican National System for registration and certification of seeds.

• In temperate zone
The breeding effort focused mainly on 2 targets : (1) new biomass sorghum hybrids as a "summer crop", (2) new biomass sorghum hybrids suitable for double cropping cycle.
SWEETFUEL is not able to recommend some biomass hybrids suitable for industrial use (biogas production or 2G ethanol production) as it requires longer time for evaluation and catalog entry. Such material must meet expectations from industrial sector which are first a good stability of biomass yield, and second a constant quality of biomass (high percentage of dry matter). If SWEETFUEL the first biomass sorghum hybrids meet expectations of quality for biogas or 2G ethanol production, stability of biomass yield is not achieved. Indeed, if we were quite satisfied with the evaluations in 2012 where some of our new hybrids performed better than the current commercial checks, the last evaluation in 2013 (with a spring particularly cold) did not result in convincing results as none of SWEETFUEL hybrids reached the level of the commercial checks. This material was evaluated for the target 1 (summer crop), which may be not the best option for European zone. Moreover in 2013 about ten hybrids made with new Sweetfuel male lines could give dry biomass yields from 18 to 26 t ha-1 with a short cycle duration (less than 110 days from sowing to harvest). These hybrids may be promising for the target 2 (double cropping systems), as the yield production is high and the dry matter content is high (>35%).
KWS and CIRAD will continue their breeding effort and test new hybrid combinations to identify material with a better stability in biomass yield for both targets.
Nevertheless SWEETFUEL produced many promising lines with a good ability fro combination, which can be tested in new combinations for new hybrids production. We can mention some A/B lines with low lignin content that can be used as female parents for developing new generation of biomass hybrids with high (enhanced) digestibility, as well as new male and new A/B female lines for biomass hybrids useful for developing new generation of biomass sorghum hybrids with short cycle duration, relevant for double cropping systems in Europe. This pre-breeding material is the main result of the breeding programme for temperate zone. It is of great value for further developments of any breeding programme targeting the two options in temperate zone. This material is available from CIRAD through Material Transfer Agreement.
Beside biomass sorghum, CIRAD also worked on identifying new sources of sweet and juicy parental lines and testing new sweet sorghum hybrids adapted to South Europe. Several of the new sweet sorghum hybrids tested at Montpellier in 2013 and 2013 summers gave excellent results (up to 5-6 t ha-1 of soluble sugars) and performed better than the current commercial checks. Such material is suitable for 1G ethanol production in South Europe where 1G ethanol production from sweet sorghum could be an opportunity according to SWEETHANOL project (Intelligent Energy Europe / http://www.sweethanol.eu).

This material is available from CIRAD through Material Transfer Agreement.


3.3. RECOMMENDATION ON CULTURAL, HARVEST AND STORAGE TECHNIQUES

Sorghum is a traditional cereal in Africa from where it originates. In the past, it was cropped to produce principally grain for human or animal consumption, but if we want to use it as an energy crop, we have to consider new cultivars: sweet (for tropical area) or biomass (for temperate zone) sorghums.
Great effort must be undertaken to inform and transfer the knowledge to farmers for giving them the best material and information on cultural practices to optimize sorghum production. This is particularly true in the case of Brazil, where the sugarcane sector has a very limited knowledge on sweet sorghum. This partially explains why they did not decide to intercrop sweet sorghum with sugarcane in the eighties, when the economic situation was quite similar to the current one. At that time, most distilleries were owned by old families that were used to crop only sugarcane and did not want to crop other plants. Nowadays, manager of distilleries are businessmen who rapidly saw the profit they could gain from the complementation of sugarcane production with sweet sorghum, and they are in favor to introduce sweet sorghum in their sugarcane rotations. But for doing this it was necessary to adapt sorghum cultural practices to a highly mechanized situation. The main challenge was to adapt and optimize the geometry of plantation to sugarcane harvester. EMBRAPA tested different densities and schemes of plantation taking into account the size of the harvester. Based on the results, a density from 120 to 130 000 plants ha-1 should be suitable for maximum ethanol production in a system combining both crops in Brazil. In other locations (India, Mexico, South Africa…) recommended plantation densities may be a little different (e.g. 110-120 000 plants ha-1 in India).
Under temperate climate, even if grain sorghum as well as forage sorghum has been cropped for a long time on limited area and the cultural practices are rather well defined. But to produce biomass for feeding biogas plants, most farmers prefer planting maize. This situation may change taking into account the advantages of sorghum in terms of nutrient and water consumption, added with the recent decision in Germany to limit at 60% the percentage of maize used to feed new biogas plants. The integrated sustainability assessment performed in SWEETFUEL pointed out that several environmental, economic and social advantages of cultivating biomass and sweet sorghum are possible, particularly through a better management of fertilizers application.
Harvest technique itself is not really an issue : in temperate zone, biomass sorghum is mechanically harvested and either used to feed directly the biogas plant, either stored as silage for a later use, while in Brazil, sweet sorghum is harvested mechanically the same as sugarcane, without collecting grain and immediately transported to be crushed in the mill. Big distilleries are well organized to collect and provide a continuous flow of feedstock to the mill that operates 24 hours a day during the high season. It is also recommended to harvest sweet sorghum at hard dough stage and defoliate the plant for a higher ethanol yield.
In countries where grain production is essential (e.g. India, Haïti…), harvesting is currently done manually. In that case, logistic can be the main issue, as the stalks must be crushed rapidly after cutting to prevent any loss of ethanol production. For small units organizing the collection could be easy, but for big units like in India for example, a continuous feeding requires to organize thousands of farmers, which may be a great challenge.
In temperate zone, the energetic and conservation properties of ensiled sorghum biomass can be improved through a mixture with lactobacillous bacteria (Figure 6).

More detailed information related to agronomy and harvest technologies is available from the "Energy sorghum handbook", as well as from Deliverables 5.3 and 5.4.


3.4. PROGRESS IN KNOWLEDGE ON PLANT FUNCTIONING

SWEETFUEL identified biological traits of interest for sweet sorghum to ensure sugar production, its combination with grain production and their maintenance under drought stress, as well as contribute to analyze the genetic bases of such traits. The phenotypic behavior of contrasted genetic material in contrasted environmental conditions, was analyzed in order to capture the impact of the variation of putative traits of interest, alone or in combination on the whole plant behavior and performance, considering possible trade-offs among traits. A particular focus was made on their regulation by water deficit and photoperiod, both known to affect plant growth and/or phenology and thus biomass, sugar and grain productions.

• Sugar accumulation
The extension of the vegetative phase due to early sowing enhances sugar production in photoperiod sensitive sweet sorghums as more internodes are initiated which have longer time to accumulate sugar. In addition, studying fertile / sterile sorghum lines pointed out that carbohydrates transported to the grain in the sterile version were not retrieved totally in the stem in the sterile plants. These observations show that early sowing of photoperiodic material is relevant to enhance sugar production and competition between sugar accumulation and grain filling is not so straightforward in the field (Figure 7).
A Recombinant Inbred Line population based on BR501R (Brandes) and BR505R (Wray) was developed by EMBRAPA. Based on genotyping and phenotyping data of this population, QTLs related to high sugar accumulation were identified. Molecular markers will be developed for selected QTLs for use in selection of superior genotypes in sweet sorghum molecular breeding programmes.

• Modeling
An existing plant growth model, Ecomeristem, initially developed for rice, was adapted to formalize the processes underlying the genetic and environmental variability of sugar and grain production. In particular, processes related to internode elongation and construction (initiation, growth, sugar accumulation), panicle formation (initiation, development, grain filling), effect of a lengthening of the vegetative phase and of modification of C source to sink relations, were formalized (Figure 8). The model was adapted, calibrated, tested and explored. Its validation and consistent application to explore ideotypes dedicated to dual production (grain, sugar) is still needed. However this modeling work performed provides today a strong cognitive and methodological basis. These results will be published in the year following the end of SWEETFUEL.
A crop model, Samara-sorghum, was also developed in the frame of SWEETFUEL. This model is available for use on sorghum research projects, either for grain, sucrose or biomass productions. It can be used as a decision support tool for agronomists, crop physiologists and breeders as it enables to test many parameters values and see how adjustment processes in the plant (e.g. tillering vs. leaf size), trade-offs among traits (e.g. plant height vs. harvest index) and trade-offs among cultural practices (e.g. plant spacing vs. varietal type) come about and affect the agronomic outcome. As a support to varietal improvement, SAMARA can be used to define the target population of environments (TPE) as well as new ideotypes according to current environments. It can also be used for climatic change mitigation studies.

• Genetic results
A study on gene expression in 2 contrasted cultivars and under 2 different water regimes allowed the identification of interesting genes linked to drought response. The next step will be to validate these genes.
QTLs for traits for high sugar accumulation were identified and allowed the development of molecular markers that can be now used in breeding programmes to select superior sweet sorghum genotypes.
Identification of QTLs for tillering, which is a very interesting trait for the development of new sweet and biomass sorghum hybrids, has been initiated, and will be completed in 2015. Molecular markers will be developed and used in breeding programmes.


3.5. SUSTAINABILITY OF ETHANOL PRODUCTION FROM BIOMASS AND SWEET SORGHUM

The integrated sustainability assessment combines, joins and extends results and conclusions from the technological assessment (Deliverable 6.2) the environmental assessment (D 6.3) the economic assessment (D 6.4) and the SWOT analysis (D 6.5) which includes social aspects. In the following the main conclusions of the integrated sustainability assessment are presented.
Scenarios on bioethanol production from sweet sorghum and scenarios on biogas production from biomass sorghum were analyzed in the SWEETFUEL project
The whole life cycles of energy sorghum cultivation and use mostly lead to a combination of environmental advantages and disadvantages (see example in figure 9). Furthermore, local environmental impacts are mostly negative, when compared to idle land. This is a typical pattern that is similarly observed for most energy crops. Effective biomass production, especially with annual or annually cultivated crops, can only be achieved with intensive agriculture including appropriate fertilization, which is the major cause for the observed negative impacts. Any weighting of these advantages and disadvantages necessarily involves subjective preferences. Thus, the precondition for any energy sorghum use is that society accepts the environmental disadvantages in return for the advantages.
Several scenarios that depict the use of mature technology turn out to be highly profitable under the conditions set for the economic assessment.

Social impacts are vary but are mostly positive as long as conflicts about land rights and access to land can be solved.

Despite these general patterns, quantitative results for environmental impacts and economic profitability can vary widely. Non-optimal scenarios can even deviate from the general pattern and cause e. g. additional greenhouse gas emissions and high economic losses. The high importance of implementation conditions emphasizes the need for optimization. The following examples for important optimization potentials can be deduced from specific analyses of individual processes and life cycle steps primarily in LCA and economic assessment:
- Yields can and should be increased by breeding highly productive sweet and biomass sorghum cultivars and by improving the agricultural management.
- The nitrogen fertilization should be reduced by breeding and management if biomass is used for energy or fuel production.

Besides variability that depends on choices of the involved shareholders, all results for future scenarios are necessarily associated with uncertainty due to external factors, which can hardly be influenced or optimized. Nevertheless, robustness of results was verified by calculating bandwidths of results under conditions that experts consider not typical but yet plausible and by sensitivity analyses e. g. on break-even prices or on replaced conventional energy sources. These analyses show the range of conditions under which conclusions based on the presented results are valid.

The integrated assessment primarily analyses whether a mature and large-scale cultivation and use of sweet and biomass sorghum in 2020 provides benefits from environmental, economic and social perspectives primarily compared to the use of fossil fuels. This sustainability assessment applies a generic and scenario-based comparison of whole life cycles from cradle to grave. It collects, joins and extends results of the preceding environmental and economic assessments as well as of the SWOT analysis, which covers further sustainability aspects especially in the social domain, and the ethical assessment. These results are integrated into an overall picture using multi-dimensional comparison metrics and a structured transparent discussion to be able to derive consistent recommendations and highlight potential conflicts.

Several scenarios regarding the production and use of sweet and biomass sorghum were defined as a common basis for all assessments of individual sustainability aspects and for the integrated assessment. Three different approaches of sweet sorghum cultivation and use are assessed in several scenarios each: cultivation on fallows between cycles of sugarcane with a focus on fuel production also from grains (“Cane fallow”), substitution of grain sorghum cultivation with co-production of food and fuel (“Grain to food”), and non-mechanized cultivation with a focus on keeping a big part of the fuel value chain in the villages through concentrating sugar juice to syrup (“Syrup production”). In all scenarios, the main product is ethanol. The main biomass sorghum scenarios involve cultivation that aims at high biomass yields for biogas production. Alternatively, the combustion of the biomass and the production of second generation fuels is analyzed (second generation ethanol via fermentation and synthetic Fischer Tropsch fuels via gasification).

Results of the integrated sustainability assessment show that the production and use of sweet and biomass sorghum can cause a wide spectrum of potential impacts ranging from significant benefits to distinctly detrimental impacts. Responsible for the individual outcome are factors such as the use of the by-products (for sweet sorghum scenarios), the choice and configuration of the conversion process (for all scenarios) but also external factors like land availability, prices and the way energy is produced elsewhere. The observed variability of results leads to concrete recommendations under which conditions and, if so, how sweet and biomass sorghum cultivation and use should be implemented.

In general, social impacts are mostly neutral to positive as long as land rights are respected. But for “Syrup production” (sweet sorghum) and 2nd generation fuel production (biomass sorghum), profitability is not immediately achievable and requires more or less substantial process improvements or subsidies depending on the assessed scenario. The profitable scenarios mostly also come along with the highest climate change mitigation and energy resource savings potentials because energy efficiency is very important for all of these aspects. To realize these potentials for environmental benefits, further optimizations are needed like the prevention of methane leaks from biogas plants, which may result in some extra costs but should not prevent profitability as such. Therefore, an implementation of sorghum-based fuel and energy production does not require continuous financial support beyond existing programs but some regulatory guidelines to improve sustainability. However, all scenarios lead to additional environmental burdens mainly caused by intensive agriculture such as acidification, excess nutrient inputs into ecosystems or detrimental local effects on soils and biodiversity. A political process is needed in each concerned region to decide how far these disadvantages are acceptable in return for the advantages. A further major limitation for sweet and biomass sorghum cultivation is the availability of agricultural land. In any case, direct or indirect clearing of valuable ecosystems for its cultivation and violation of land rights have to be avoided. In this respect, specific advantages of sorghum should be taken advantage of to mitigate competition about land:
- For sweet sorghum, the use of co-products such as grains and surplus bagasse, which is not required for powering the conversion process, as feed or food can reduce the demand of land for separate food/feed production elsewhere. This way, an integrated production of these products and fuels on the same land using sweet sorghum may in some cases even suffice with less total area than separate cultivation without fuel production.
- For biomass sorghum, drought tolerance and resistance against a certain pest may open up opportunities for cultivation, which are not available to competing energy crops such as maize.

Land availability is a general limitation for cultivation of all energy crops and thus also for energy sorghum. Conflicts about land can be mitigated if land that can be used is not or not very well suited for established crops. This does not only refer to m