If non-food cellulosic ethanol — “celluline” — is the future of sustainable biofuels, what are the best non-food crops to use to make it?
In a new study, researchers have shown that growing perennial grasses to make celluline rather than using corn stover or sugar cane is better for the environment because it increases soil health and stores much more carbon in the soil, thereby reducing greenhouse gases.
Current first generation ethanol is produced by fermenting the starch in corn kernels. This has become a controversial source of biofuel due to food vs. fuel concerns and the relatively low energy gain from the whole process.
But celluline represents a true departure from these concerns in that significantly more liquid fuel energy can be harvested from non-food portions of the plant — the stems and leaves. Celluline is still in the research and development stage, but many people have hung their hats on it as the holy grail that will replace corn ethanol and bypass concerns over food vs. fuel and energy gains (PDF).
As a bit of a refresher: plants use the sun’s energy to convert carbon dioxide from the atmosphere into various plant parts such as leaves, stems, and roots. A large portion of the carbon in the leaves, stems and roots eventually ends up as organic carbon in the soil (roughly 5% of a healthy soil is organic carbon).
The organic carbon in soil is a major sink of carbon dioxide from the atmosphere. Whenever the soil is worked due to farming, construction, gardening or anything else, some of this carbon returns to the atmosphere in the form of carbon dioxide.
The problem with using corn, and other annual crops such as sugarcane, is that they need to be replanted every year. This repetitive working of the soil creates a carbon deficit that can take years to build back using the best management strategies available and in the meantime you’ve released more carbon dioxide into the atmosphere than you’re trying to save by using biofuels in the first place.
On the other hand, the researchers found that perennial grasses like miscanthus, switchgrass and native prairie grasses, have a small initial carbon release associated with planting, but after that they start acting as a carbon sink very quickly.
So, in terms of dealing with climate change, if we’re going to turn to biofuels as part of our energy mix in the future, it looks like perennial grasses are the hands-down winner.
Image Credit and Source: EurekAlert!
The findings from this study will appear next month in the journal Global Change Biology Bioenergy.