This topic is being discussed elsewhere, so I thought I’d post something on it:
Back to the future: Prairie grasses emerge as rich energy sourceMixtures of grasses make best source of biofuel By Deane MorrisonDec. 8, 2006With shrinking glaciers and other signs of global warming upon us, the search is on for alternative fuels to stem the release of greenhouse gases such as carbon dioxide into the atmosphere.This week a new contender burst on the scene: diverse mixtures of native prairie grasses. A University team led by David Tilman, Regents Professor of Ecology, found that these grasses yield more net energy than either ethanol from corn or “biodiesel” fuel from soybeans. Grass-based fuel can even lead to a net decrease in atmospheric carbon dioxide, whereas ethanol and biodiesel increase it.The study is based on 10 years of work at the University’s Cedar Creek Natural History Area. Written by Tilman, postdoctoral researcher Jason Hill and research associate Clarence Lehman, it is the cover story in the Dec. 8 issue of the journal Science.[source]
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I’ve been hearing of a large number of interesting energy developments lately, mostly through CBC’s “Quirks and Quarks” radio program. This week was using bacterial metabolism substantially reduce the amount of electricity required to convert water into Hydrogen and Oxygen. A few months back, it was biodegradable sugar-powered fuel cells.Hydrogen ad Bacteria:http://www.cbc.ca/quirks/archives/07-08/dec01.htmlPower, Sweet Power:http://www.cbc.ca/quirks/archives/06-07/mar31.htmlOlder, not as nigh-practical, but still cool:A New Solar Power:http://www.cbc.ca/quirks/archives/04-05/jan29.html
Food cereals put down roots about a foot. Prairie grasses put roots down about three feet, so they condition much more of the soil, make far better use of water and nutrients, recover faster after being mowed, and they are not just hardy, they are almost impossible to eradicate, unlike monoculture cereals which are much more vulnerable to pests.
But how does it compare to planting trees on the same acreage and burning normal diesel?from the article:”LIHD biomass removed and sequestered more atmospheric CO2 than was released from fossil fuel combustion during agriculture, transportation, and processing (0.32 Mg ha�1 year�1 of CO2), with net life cycle sequestration of 4.1 Mg ha�1 year�1 of CO2 for the first decade and an estimated 2.7 to 3 Mg ha�1 year�1 for subsequent decades.”So call it 100 Mg of carbon dioxide/ha over 30 years, or about 27 Mg of carbon.An earlier article in Sciencehttp://www.sciencemag.org/cgi/content/full/317/5840/902?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=forest+biofuel&searchid=1&FIRSTINDEX=0&resourcetype=HWCITputs the net sequestration of carbon from reforesting temperate cropland at almost 100 Mg/ha of carbon over 30 years.I’ve probably missed something, but it looks like planting trees and leaving them there still has a three to fourfold advantage over harvesting grasslands for fuel.
I can see two problems. First, Forests aren’t permanent methods of sequestering carbon. Forests burn, plants decompose and are metabolized by it’s inhabitants. Eventually those forests reach a level of equilibrium. It’s just not a useful way of dealing with the external source of carbon (fossil fuels) we’re pumping into the cycle, unless we then bury the forests and plant a fresh one on top of it to take it out of the cycle permanently.At least with biofuels, the carbon we put into the atmosphere came out of the atmosphere tin the first place. As long as harvesting, processing and distribution are using green sources of power, the whole system is carbon neutral.The second issue isn’t really one of global warming, but the scarcity of fossil fuels. If indeed the peak oil theorists are right, we can expect to see higher prices, and eventually worldwide shortages. Better to get off those fossil fuels as much as possible while we still have cheap energy, rather than wait until the last second to try and make drastic changes.