Dr Akhil Verma
Sorghum is the ‘King of Millets’ and a dual-purpose crop mainly grown for its grain and fodder, it is also known by various vernacular names such as great millet, jowar, charri etc. Sweet sorghum is similar to usual sorghum except for its juice-rich sweet stalks and it is often taller, reaching up to height of 4 meters. It can be grown successfully in semiarid tropics, where other crops are unable to grow satisfactorily. It is a versatile and resilient crop that holds a distinct place in the realm of agriculture. It has multifaceted applications as it is a source of food grain, forage, feed, fuel besides it has sweet juicy stalks. Owing to its very high palatability, sweet sorghum is more sought as forage crop by the dairy farmers. Sweet sorghum has some interesting characteristics like it has short growth cycle, facilitating double cropping. It serve as a valuable source of nutrition such as carbohydrates, proteins, vitamins and minerals. It has a high water and nutrient use efficiency. The advantages of the crop are that it can be grown with limited water and minimal inputs. It is also found to be more promising than forage sorghum and even corn in green forage productivity and quality. contributing to sustainable intensification strategies in livestock sector.
Sweet sorghum is a warm-season crop that matures earlier under high temperatures and short days. It tolerates drought and high-temperature stress better than many crops and hence adapts well to sub-tropical and tropical regions of the world besides it is highly efficient in biomass production. Atmospheric temperatures suitable for its growth vary between 15oC and 37°C. Sweet sorghum can be grown under dryland conditions with annual rainfall ranging from 550?750 mm. It can be grown on well-drained soils such as silt loam or sandy silt clay loam soils with a depth 0.75m. Sorghum being a C4 species is adapted to wide range of environments. Sweet sorghum can extract water from deeper layers upto 270 cm of soil depth. it can transform the available water more efficiently into dry matter than most of the other C4 crops. Owing to high photosynthetic efficiency coupled with dry matter production it is considered as an important energy crop for production of fuel bio-ethanol. Sugar stalk crops, such as sugarcane and sweet sorghum, offer more advantages than other crops since they produce a solid residue (bagasse) which can be used as a source of fuel to generate energy, as animal feed or as soil fertilizer after composting with other agro-wastes. The utilization of bagasse has a most promising future for its bio-conversion to cellulose-based ethanol, while the residual solids (mainly lignin) can be incinerated to co-generate heat and power. Besides, sweet sorghum has a panicle with grains that may be used either as food or feed. Some recent research reports suggest that soluble sugars produced in sweet sorghum has a potential to yield up to 8,000 litre of ethanol per hectare or about twice the ethanol yield potential of maize grain and 30 % greater than the average sugarcane having productivity of 6,000 litre per hectare. Intensive research efforts are underway in various countries viz., USA, China, India, Africa, Indonesia, Iran and Philippines to assess the agro-industrial potential of sweet sorghum. High-yields, drought tolerance, relatively low input requirements in terms of water and fertilizer along with its ability to grow under a wide range of agro-climatic conditions makes it a wonderful crop for ethanol production.
The Government of India’s policy to blend petrol with ethanol to reduce fuel-import bill and environmental pollution, initially up to 5% has triggered production of bioethanol from different feedstocks. Requirement of ethanol in the country is estimated to be around 0.64 billion liters annum-1 at the 5% level of doping in petrol. Currently, molasses is the sole feedstock to produce alcohol. The price of molasses is highly variable between 2000 and 6000 ton-1 and cost of ethanol production from molasses also varies accordingly. The process of ethanol production from molasses is highly polluting as molasses itself is a byproduct from sugar industry. Also, production of ethanol from molasses alone is unlikely to meet the requirement of ethanol for doping with petrol at 5%, as the scope for increasing sugarcane area beyond the current 5.76 million hectare in the country is feeble due to depleting water reserves and shrinking land area available for cultivation. Therefore, researchers and policy makers are exploring alternative feedstock for ethanol production. Sweet sorghum is similar to grain sorghum, but accumulate sugars (10?15%) in its stems/stalks as in sugarcane. It is a potential alternative feedstock with less water and input requirement than those of sugarcane from which molasses is obtained. Ethanol produced from sweet sorghum stalk juice by fermentation and distillation is similar to that produced from sugarcane molasses, but without any pollution hazards.
Sweet sorghum is mainly grown during kharif (June- October) season. The crop can also be grown during rabi (October- Feburary) and Summer (Feburary to May). Rabi and summer plantings must be under assured irrigated conditions besides October planting should be done areas which are less prone to frost. Seed rate of 8 kg ha-1 (or 3 kg acre-1) is suffient, sown at spacings of 60 cm between rows and 15 cm between plants. Earthing-up required between 20 to 35 days after sowing. 80 kg nitrogen ( in three splits i.e, 50 % first dose at sowing and remaining 50% top dressed in two equal splits 30-35 days and 45-50 days after sowing) along with 40 kg phosphorus and potassium each at sowing time are needed for fertilization. Irrigation as per requirement. The sweet sorghum crop takes 3-4 months to reach maturity. Harvesting should be done at about 40 days after flowering of the plants, i.e., at physiological maturity of grain Alternately, the Brix of standing crop can be measured using hand Refractometer. Harvest of the stalks should be done at the ground level and leaves including sheaths needed to be removed.
The biofuel distilleries need continuous supply of raw material, i.e., sweet stalks for a major period of the year to be commercially viable. It is advantageous to explore the possibility of ratooning not only to extend the raw material supply to the distillery but also to reduce the cost of feedstock production as well as to facilitate relay cropping to maximize the returns on land and labour. Interestingly, from different field research trials conducted by National Dairy Development Board, Gujrat it has been observed that sweet sorghum can be harvested twice as ratoon crop.
It is not often that all the three (Food, Fodder and Fuel) requirements can be met by one single crop. It provides grain for human consumption and stover for fodder and it is also used for industrial biofuel production. It is a way forward towards doubling farmers income besides achieving food and nutritional security along with our objective of crop diversification. Sweet sorghum extracts only one fourth of the water (4000 m3) that is used up by sugarcane (36000 m3). Since, sweet sorghum can tolerate water stress and can be successfully cultivated in dryland conditions, it is a crop that can accomplish our worthy prime minister’s slogan of Per Drop More Crop.
UT of Jammu and Kashmir, has large area under rainfed cropping with low cropping intensity of 156.7% while less than 4% arable land is under fodder cultivation and facing a 54% deficit in green and 27.3 % dry fodder, respectively. Sweet sorghum can be a promising crop for this region being a low water and fertilizer demanding. It can provide nutritious grain for food and feed with sweet juice extraction of 35% from its stalk that can be utilized for different industrial purposes having prospects to push the industrial growth. Cost of sweet sorghum seed is approximately 400/- per kg which is at least 7 times higher than normal sorghum. This implies that even if Sweet sorghum produced for seed purpose alone it will still be highly remunerative. It has also potential to provide green fodder to the tune of 45 to 50 t/ha and is excellent crop for silage making. Some farmers in Gharani area, R.S Pura of Jammu show encouraging response from sweet sorghum being exclusively grown for green forage. Sweet sorghum holds promise to achieve multiple objectives of environmental safety, crop diversification, value addition, resource conservation, food, nutritional and economic security which are unlikely to be harnessed from any single crop alone. Thus, introduction of new generation futuristic crops like Sweet sorghum in our agriculture production system is the need of the hour.
(The author is a Professor of Agronomy at Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu)
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