**Sweet Sorghum: A dryland-adapted, pro-poor bioethanol feedstock
yielding both grain and fuel**[^1]

Belum VS Reddy, A Ashok Kumar and P Sanjana Reddy[^2]

www.icrisat.cgiar.org

Nations are investing heavily to increase their energy security and
reduce their fossil-fuel carbon emissions and pollution. But they are
also justifiably concerned that the bioenergy revolution could
marginalize the poor, raise food prices and degrade the environment.
Sweet sorghum (*Sorghum bicolor* L. Moench) can be harvested green or at
maturity to produce grain as well as the stalks for bioethanol
feedstock, thus reducing the food-fuel tradeoff issue. It is adapted to
lower-rainfall tropical environments (approximately 800 mm over a
five-month rainy season) mainly inhabited by poor smallholder farmers.
Breeding research to enhance the competitiveness of this feedstock can
therefore contribute to pro-poor dryland rural development.

The stalks of sweet sorghum harvested just before flowering contain
almost as much sugar as sugarcane (16-23% Brix). When grown to maturity,
stem sugar content declines by about 25% (in moderately early varieties)
but farmers gain added income and food from the grain. Thus it provides
options for both food and biofuel production, and is suitable for
smallholder farmer cultivation on less-favored lands. Besides having
wide adaptability, rapid growth and high sugar accumulation and biomass
production potential, sweet sorghum, is tolerant to drought, water
logging, soil salinity and acidity.

Under socio-economic conditions prevailing in India, the cost of ethanol
production per liter from sweet sorghum juice is competitive with that
of sugar cane molasses, and significantly less than with maize grain as
feedstock. Hybrid seed technology could create a major advance economic
competitiveness, as well as in productivity of both grain and
bioethanol. Like sugarcane, sweet sorghum bioethanol systems also yield
a highly positive net energy balance (Energy output/fossil energy input
estimated at approximately 8), roughly four times higher than for maize
grain as feedstock in the USA.

The biomass based (cellulosic) ethanol production technology helps fight
global warming. Sweet sorghum is an excellent source of biomass as it
yields 30-35 tonnes of biomass per ha in 4-5 months. When harvested
green it is succulent and rich in cellulose (15-25%) and hemicellulose
(35-50%), making it amenable for microbic digestion and fermentation.

Lignin, the non-sugar structural component ranges from 20-30% in cell
wall in sweet sorghum. Brown midrib genotypes have reduced lignin
content (up to 50% less), which helps reduce the cost of enzyme
requirement for converting cellulose to glucose. ICRISAT is focusing on
development of photo and thermo-insensitive sweet sorghum hybrid parents
with high Brix and brown midrib hybrids to facilitate the bioenergy
production using first and second generation ethanol production
technology while ensuring the grain yield potential for food security.
The stillage (main frame of the plant) obtained after crushing the cane
is an excellent animal feed.

In addition to building on the pro-poor characteristics of this crop,
proactive steps need to be taken to engage large numbers of smallholder
farmers in the production and market chain. They must become productive
and economically competitive with alternative large-farm models that
could marginalize them. ICRISAT is researching partnership models by
incubating this technology with Rusni Distillery Ltd., in India.
Subcontracting arrangements provide farmers with credit and assured
price and market, and access to inputs such as fertilizer, hybrid seed
and training supplied by the processor. The model also supports research
to generate a sustained flow of system innovations. The processor
benefits from predictable feedstock costs and reliable feedstock
supply-chain efficiency.

[^1]: Abstract of the paper to be presented at USDA Biofuel Conference,
    20-22 August 2007, At Minneapolis, Minnesota, USA.

[^2]: Principal Scientist, Scientist and Scientific Officer,
    International Crops Research Institute for the Semi-Aid Topics
    (ICRISAT), Patancheru 502 324, Andhra Pradesh, India: First author
    email: b.reddy@cgiar.org