The widespread practice of burning sugar cane prior to harvest is becoming a challenge, particularly in Southern Africa, as it causes air pollution and biomass residue (cane trash), which could otherwise be burned to generate heat and create electricity, says global policy research institute Stockholm Environment Institute (SEI) senior research fellow Francis Johnson.
Sugar cane farming also poses other environmental threats, including potential negative effects on biodiversity and ecosystems by occupying large contiguous plots of land and by causing runoff of nutrients, leaching pesticides and chemicals into the soil, the eutrophication of waterways from fertiliser and discharging of organic pollutants from sugar mills and ethanol distilleries.
“The additional water being used for irrigation in sugar farming regions in South Africa may exacerbate water stress. Even without irrigation, sugar cane can remove water resources from other crops, owing to soil and groundwater evapotranspiration needed to support sugar plant growth,” says Johnson.
He says, to some extent, all African countries that have sugar cane farms face these problems. “Most countries have some legislation that regulates agriculture and, in some cases, particularly sugar cane. “However, the enforcement of regulations for proper farming practices may be difficult and poorer countries tend to have difficulty in fully implementing legislation.”
He adds that countries, in which sugar crops are irrigated, such as South Africa and Egypt, are contributing to the increasing global problem of water stress and scarcity.
“There are other African countries that irrigate or are planning new projects that include irrigation. “Sugar cane is a thirsty crop in terms of water use, but as it produces a considerable amount of biomass, along with sucrose stored in the stalk, the water for each unit of energy potential will often be lower than other conventional crops,” says Johnson.
He highlights that the capacity of sugar cane to grow rapidly has made it the world’s number one energy crop.
However, sugar cane is a monoculture and an industrial crop – it therefore requires considerable input to maintain high productivity for each unit area.
“In some ways, this high productivity contributes to sustainability, as the land area required in relation to the high economic return is small, compared with other crops,” says Johnson. “The high productivity means that, in some cases it can actually take pressure off land resources located elsewhere and thereby indirectly contribute positively to biodiversity and ecosystem health,” says Johnson.
He adds that if environmental standards pertaining to sugar farming are to be improved, a key issue will be to cultivate sugar cane on land that is suitable in terms of soil, climate and water availability.
He says countries, such as Mauritius, have adopted a modern way of farming sugar cane, resulting in higher efficiency and productivity, while reducing the environmental impact.
“In some cases, this is being done at the expense of employment in Mauritius, since the manual cutting of cane may be replaced with mechanised harvesting,” says Johnson.
Other approaches to reduce environmental impacts are undertaking agroecological zoning, which informs companies of the most suitable lands for growing sugar cane; best management practices, such as low tillage or no tillage, precision irrigation and nutrient delivery; and the selection or breeding of sugar cane varieties that are better suited to a particular location.
Johnson highlights that all of these practices are becoming widespread in Brazil, where the goal is to reduce environmental impacts.
“Farmers can also choose different crops when sugar is not the main concern, such as sweet sorghum – which is most suitable for ethanol and electricity production – rather than crystalline sugar,” says Johnson.
Future of Sugar Cane
SEI says the sugar cane industry is making good progress in many respects, as its high productivity results in much lower land use and environmental impacts – in relation to biomass yield – compared with crops such as soya or maize.
“A key issue for the future is the role of sugar cane as part of a biorefinery complex, which contributes to the development of the global bioeconomy,” says Johnson.
As the sugar cane crop provides both biomass and sugars, there are opportunities to produce food, fuel (ethanol), electricity, chemicals, bioplastics and fertilisers from the crops which all belong to the same biorefinery complex.
“These bio-based materials can be used as substitutes for fossil-based products, thereby improving sustainability by producing renewable materials through bio-based processes,” Johnson concludes.