Sweet sorghum is a hardy, nutritious, biofuel crop that offers solutions in drought-hit southern Africa

By Hamond Motsi, Stellenbosch University

The southern African region is battling with drought at present. This is the result of El Niño, a natural climate cycle characterised by changes in Pacific Ocean temperatures. It has effects on global weather patterns, particularly rainfall and temperature.

The drought has hit the region’s agricultural productivity hard. Malawi, Zambia and Zimbabwe have declared a state of disaster with respect to their current agricultural outputs. They are seeking humanitarian assistance in the form of food aid to feed their people. The downturn also has economic implications, since over 70% of people residing in the region’s rural areas rely on agriculture for their livelihoods.

The dire situation underscores how important it is for the agricultural sector to prevent, avoid or prepare for the impacts of climate change, which will also bring extremes of weather.

One measure the sector can take is to cultivate biofuel crops. These are crops rich in starch, sugar or oils that can be converted into bioethanol directly or through a fermentation process. Bioethanol, a type of ethanol produced from biological or plant based sources, emits fewer greenhouse gases compared to fossil fuels like petroleum, natural gas and coal. Commonly used biofuel crops include sugarcane, maize, grain sorghum, sugar beet, rapeseeds and sunflower.

These conventional biofuel crops do have drawbacks, however. They are highly susceptible to extreme weather events. They require high upfront investment for fertilisers, chemicals and irrigation. And they compete with food production – if they’re grown as biofuels they can’t also be used as food because of how they have to be processed.

So, researchers are always on the lookout for crops that might be good biofuels without those problems. Sweet sorghum, which is indigenous to the African continent, is one such crop. Unlike the better-known sorghum, it has sweet juice in its stems. In a recent study, I reviewed scientific literature to analyse the potential significance of sweet sorghum to African farmers because of its multipurpose nature and ability to adapt under harsh climatic conditions.

Multiple uses

Sweet sorghum has many uses. It can produce grains, animal feed and sugary juice, making it unique among crops.

The grains from sweet sorghum are prepared as steamed bread or porridge malt for traditional beer, as well as in commercial beer production across the continent.

They’re nutritionally rich, with high energy values (342 calories/100 g), proteins (10g/100 grains), carbohydrates (72.7g/100 grains), and fibre (2.2g/100 grains) as well as essential minerals such as potassium (44mg/100 grains), calcium (22mg/100 grains), sodium (8mg/100 grains) and iron (3.8mg/100 grains).

The nutritional value of maize is fairly similar: proteins (8.84g/100 grains), carbohydrates (71.88g/100 grains), fibre (2.1g/100 grains), potassium (286mg/100 grains), calcium (10mg/100 grains), sodium (15.9mg/100 grains) and iron (2.3mg/100 grains).

What sets sweet sorghum apart from a crop like maize is that it’s also resilient in arid climates and has multiple other uses. For instance, it produces a lot of plant material (biomass) as it grows, which is left over after harvest. That’s why it’s useful as animal feed too.

Animal feed is made from what remains once the sweet sorghum crop has been harvested and its grains and stem juice stripped off. The residue is high in nutritional content, which can improve the quality of diets of animals, including cattle. The grains can also be used for animal feed.

The sweet juice in the crop’s stalks is what’s used to create bioethanol. Sweet sorghum contains sucrose, glucose and fructose, which are essential for bioethanol production. Of the conventional biofuel crops I’ve mentioned, only sugarcane yields more ethanol. Studies in the United States have shown that sweet sorghum far outstrips maize when it comes to bioethanol production: it yields 8,102 litres per hectare planted, while maize yields just 4,209 litres per hectare.

Resilient

Perhaps most importantly given the southern African region’s current drought struggles, sweet sorghum is well-suited for cultivation in the sorts of adverse conditions that are typically challenging for conventional biofuel crops.

One of the key characteristics of sweet sorghum varieties is their drought resistance. It allows them to enter a dormant state during extended periods of dryness and resume growth afterwards. Research has shown that, under intense water scarcity conditions, sweet sorghum makes use of its stalk juice to supplement its plant needs.

Sweet sorghum’s ability to withstand low water and nitrogen inputs, as well as its tolerance for salinity and drought stress, makes it an ideal crop for farmers in arid regions. This is why it’s widely used in other parts of the world, including the US, Brazil and China.

Investing in sweet sorghum

The continent’s current agriculture value chain is dominated by major crops like maize, wheat and rice, which all originate from outside Africa. Not enough attention is given to crops of African origin, like sweet sorghum, even though it is a multipurpose, hardy crop with great potential for farmers. People are more familiar with sorghum, not the sweet variety, and it is also under-researched.

Governments should be using their agriculture extension services to raise awareness among farmers and consumers about the benefits and practical applications of sweet sorghum in people’s diets.

Developing recipes and secondary or industrial products can enhance the feasibility and awareness of sweet sorghum farming. By investing in research and development, the full potential of sweet sorghum cultivation can be unlocked through governments and the private sector.

Hamond Motsi, PhD Student in Agriscience, Stellenbosch University

This article is republished from The Conversation under a Creative Commons license. Read the original article.