Sorghum as a Multifunctional Crop for the Production of Fuel Ethanol: Current Status and Future Trends

Abstract

Nowadays, there is a growing interest for alternative energy sources because of the reduction of fossil fuel production. Ethanol used as automotive fuel has increased at least six times in the current century. According to the Renewable Fuels Association, in 2010 the USA bio-refineries generated 13 billion gallons of fuel ethanol and the year before worldwide production reached 19 billion. This noteworthy increment is in its majority based on maize and sugar cane as raw materials (Berg, 2004; Renewable Fuels Association, 2010). The use of these feedstocks has triggered concerns related to food security especially today when the world population has reached 7 billion people. The relatively sudden rise in food prices during 2008, 2010 and 2011 has been attributed mainly to the use of maize for bioethanol even when other factors like droughts or changes in global consumption patterns have also played a major role (World Food Program, 2008). Food price projections indicate that this situation will worsen, breaking the downward trend registered in food prices in the last thirty years (The Economist, 2007). Even if there was not a food-fuel controversy especially due to the current conversion of millions of tons of maize for bioethanol, the use of only this crop cannot support the ambitious objectives of renewable fuel legislation in countries like the United States of America, where a target of 36 billion gallons of liquid biofuels have been established for 2022. In order to meet this requirement all the 333 million tons of maize yearly produced by USA should be channelled to biorefineries. This production represents 2 and 16 times the maize harvested in countries like China and Mexico respectively, which in turn are two of the five top world producers. Environmental factors have been also pushing for the quest of new crops dedicated exclusively for liquid automotive fuel in order to reduce the use of prime farming land, irrigation water and other resources. A dedicated energy crop ideally must meet several requirements such as: high biomass yield and growth rate, perennial, with reduced input necessities, fully adapted to the geographic regions where will be planted, easy to manipulate via genetic improvement, non-invasive, tolerant to stress and with a good carbon sequestration rate among others (Jessup, 2009). At the present time, energy crops are