Jan 3, 2013
Can Ghana match Brazilian sugar-cane yields?
Increasing fossil-fuel prices are making biofuels more popular. But can biofuels be grown sustainably, and on a large enough scale to meet the growing demand? And how will climate change impact the yields of biofuel crops? A new study investigates the feasibility of expanding global biofuel production.
For farmers in the developing world, energy crops are a tempting prospect, and already some developing countries are starting to move into the market. For example, in 2008 Brazil's agriculture research agency, EMBRAPA, opened an office in Accra with the intention of helping Ghana to build up its nascent ethanol industry. In 2010 Brazil made a $300 m investment in exporting Brazilian sugar-cane cultivation and refinement technology to Ghana. In addition a dam has been proposed on the River Daka to provide irrigation water for this thirsty crop.
Taking sugar cane in Ghana as a case study, Emily Black from the University of Reading, UK, and colleagues investigated what kind of yields could be expected when sugar cane is grown in Ghana, and how future climate change might impact those yields. Using a process-based crop model they were able to compare the expected yields in Ghana with the actual yields achieved currently in Brazil.
In their model the researchers assume that plant growth is not limited by nutrients, but take into account the hotter climate and more variable rainfall in Ghana, compared to São Paulo, the major sugar-cane growing region of Brazil. They found that even with plentiful irrigation, yields in the Daka River region of Ghana can only expect to approach 75% of the yields achieved in the São Paulo region. "Our results suggest that the higher mean temperatures and differences in the temperature seasonal cycle reduce the yield," said Black, whose findings are published in Environmental Research Letters (ERL).
Preliminary results from a hydrological study of the Daka River region indicate that a dam could just about provide enough water to irrigate the proposed sugar-cane crops. "There may also be other benefits to the dam, such as a more perennial river flow and a reduction of flood risk," Black told environmentalresearchweb.
Meanwhile, the model suggests that the impact of increasing temperature on crop yields may be surprisingly small. In the case of C4 crops, such as sugar cane, increased carbon dioxide decreases stomatal conductance of the plant and hence reduces transpiration. "This means that an increased carbon-dioxide concentration could ameliorate the water stress associated with temperature increase, and allow the crop to sustain its growth," said Black.
However, Black stresses that the model's results should not be taken as a climate-change scenario, as the team did not take into account other aspects of climate change such as changes in precipitation, radiation and humidity, which could have adverse effects on crop yield.
For Ghana at least, the model has shown that growing sugar cane for energy crops is feasible, but not without difficulties. In a rapidly changing world models like this will be a vital tool to ensure that energy crops are grown in the most suitable locations, and costly and unsustainable mistakes are not made.
About the author
Kate Ravilious is a contributing editor for environmentalresearchweb.