Switchgrass into ethanol
Large scale study shows 540% net energy gain when ethanol is produced from switchgrass
Panicum Vergatum: Switchgrass
Courtesy U S Govt
Kenneth Vogel, a geneticist with the U.S. Department of Agriculture in Lincoln, Nebraska, and his colleagues, found that ethanol produced from switchgrass yields 540% of the energy used to grow, harvest, and process it into ethanol.
Their results, published online in Proceedings of the National Academy of Sciences, shows that switchgrass, farmed using conventional agricultural practices on less-than-prime cropland yields only slightly less ethanol per hectare on average than corn.
Farmers planted switchgrass on 10 farms, each of which was between 3 and 9 hectares. They then tracked the inputs they used--diesel for farm equipment and transporting the harvested grasses, for example--as well as the amount of grass they raised over a 5-year period. ScienceNOW Daily News
Switchgrass monoculture or mixed prairie grasses?
Anyone remember our Buzz post "Chalk one up for diversity"? David Tilman in that post is quoted saying, "diverse prairie grasslands are 240 percent more productive than grasslands with a single prairie species"
Now I read:
... Vogel says, is that yields on farms using fertilizer and other inputs, such as herbicides and diesel fuel for farm machinery, were as much as six times higher than yields on farms that used little or no fertilizer, herbicides, or other inputs to grow a mixture of native prairie grasses. ScienceNOW Daily News
Who is right? Can anyone explain why two reputable researchers are getting such different results?
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National Geographic on line just put up a post on this titled, "Grass Gas" Shows Promise as Superefficient, Clean Fuel.
It sounds to me like Tilman and Vogel are describing two unrelated phenomena. Tilman says a plot of land with multiple species of grass is more productive than that same plot with only one species. Vogel, meanwhile, seems to be saying that a mixed-species plot grown using fertilizer and herbicides is more productive than a mixed-species plot grown without them. They're making their comparisons on different bases.
The habitats where the research was done is different and the plants used were different so this may have influenced the out comes of the experiments.
Here's another wrinkle to the fabric. The Tillman study used small hand-weeded plots, which you can't scale up. Vogel's research uses large realistic plots. Also, they were studying different aspects of the same sort of system, perhaps diverse species, with some farm inputs can be the best combination?
The two studies were very different because of the reasons others have commented on. However, both studies use the assumption that cellulosic ethanol is or will shortly be a ready to use technology. I'm not so convinced that cellulosic technology will imminently justify building full scale production facilities.
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