December 07, 2006
Monocultures Not Best Choices For Biomass Energy

University of Minnesota researchers say that monoculture agriculture is not the best way to produce biomass energy.

Diverse mixtures of native prairie plant species have emerged as a leader in the quest to identify the best source of biomass for producing sustainable, bio-based fuel to replace petroleum.

A new study led by David Tilman, an ecologist at the University of Minnesota, shows that mixtures of native perennial grasses and other flowering plants provide more usable energy per acre than corn grain ethanol or soybean biodiesel and are far better for the environment. The research was supported by the National Science Foundation (NSF) and the University of Minnesota Initiative for Renewable Energy and the Environment.

"Biofuels made from high-diversity mixtures of prairie plants can reduce global warming by removing carbon dioxide from the atmosphere. Even when grown on infertile soils, they can provide a substantial portion of global energy needs, and leave fertile land for food production," Tilman said.

The findings are published in the Dec. 8, 2006, issue of the journal Science.

Mixtures of plant species work better on land that is less than ideal.

The is study based on 10 years of research at Minnesota's Cedar Creek Natural History Area, one of 26 NSF long-term ecological research (LTER) sites. It shows that degraded agricultural land planted with diverse mixtures of prairie grasses and other flowering plants produces 238 percent more bioenergy on average than the same land planted with various single prairie plant species, including switchgrass.

One of the problems I have with the corn biomass ethanol approach is that the land which is not currently used to grow corn is far worse for that purpose than the land which still is used to grow corn. These researchers, by looking at what works best on poorer quality land, are looking for ways to make biomass energy production scale.

"This study highlights very clearly the additional benefits of taking a less-intensive management approach and maintaining higher biodiversity in the process," said Henry Gholz, NSF LTER program director. "It establishes a new baseline for evaluating the use of land for biofuel production."

Tilman and his colleagues estimate that fuel made from this prairie biomass would yield 51 percent more energy per acre than ethanol from corn grown on fertile land. Prairie plants require little energy to grow and all parts of the plant above ground are usable.

Fuels made from prairie biomass are "carbon negative," which means that producing and using them actually reduces the amount of carbon dioxide (a greenhouse gas) in the atmosphere. Prairie plants store more carbon in their roots and soil than is released by the fossil fuels needed to grow and convert them into biofuels. Using prairie biomass to make fuel would lead to the long-term removal and storage of from 1.2 to 1.8 U.S. tons of carbon dioxide per acre per year. This net removal of atmospheric carbon dioxide could continue for about 100 years, the researchers estimate.

In contrast, corn ethanol and soybean biodiesel are "carbon positive," meaning they add carbon dioxide to the atmosphere, although less than fossil fuels.

These researchers do not see switchgrass as the great biomass hope that others portray it to be.

Switchgrass, which is being developed as a perennial bioenergy crop, was one of 16 species in the study. When grown by itself in poor soil, it did not perform better than other single species and gave less than a third of the bioenergy of high-diversity plots.

"Switchgrass is very productive when it's grown like corn in fertile soil with lots of fertilizer, pesticide and energy inputs, but this approach doesn't yield as much energy gain as mixed species in poor soil nor does it have the same environmental benefits," said paper co-author Jason Hill, also of the University of Minnesota.

So far monocultures have been the only way biomass energy has been produced. Therefore these researchers are arguing for quite a departure from current practice.

To date, all biofuels, including cutting-edge nonfood energy crops such as switchgrass, elephant grass, hybrid poplar and hybrid willow, are produced as monocultures grown primarily in fertile soils.

But the amount of energy they expect to get from using mixed prairie grasses on less than ideal land is still far from enough to replace all uses of oil. Worse yet, the world demand for energy is going to keep going up.

The researchers estimate that growing mixed prairie grasses on all of the world's degraded land could produce enough bioenergy to replace 13 percent of global petroleum consumption and 19 percent of global electricity consumption.

My guess is they are assuming future cellulosic technologies to extract the energy out of the grasses. So a shift toward prairie grass for energy isn't practical yet.

My main objection to biomass remains that land pushed into production to produce energy is land not available to serve as habitat for a wide assortment of species. Want to see more animals go extinct? Promote biomass. The land footprint of nuclear power is far smaller and even photovoltaics would use a much smaller footprint to produce the same amount of energy as biomass.

Update: See the extensive debate at The Oil Drum on this research. Some of the posters throw doubt on the use of marginal lands with the argument that the biomass yield per acre will be so low that this will cause high harvesting costs per amount of energy gained.

Lower yield per acre also translates into far more acres used to produce energy. This cuts more heavily into habitats and threatens species. We need to move to nuclear, photovoltaics, and even wind power. Damage to habitats from biomass energy will cancel out any benefits from reduced CO2 emissions.

Share |      Randall Parker, 2006 December 07 11:31 PM  Energy Biomass

anonrobt said at December 8, 2006 8:19 AM:

Of course, what's also not mentioned is that the area of poor land for this use is also one in which the harvesting is more difficult, thus requiring more energy output to acquire, thus less gain, if any...

Wolf-Dog said at December 8, 2006 4:56 PM:

There will certainly be a lot of new genetically engineered biomass plants, including genetically improved switchgrass to grow on infertile lands. But using biomass to make alcohol is still a less logical idea, given that it is several times more economical to burn the biomass directly in furnaces to make electricity, and then use this electricity to charge electric cars. This is the fastest and the easiest method, but automobile companies as well as the oil companies would find it more profitable to make traditional liquid fuels from biomass, in order to continue manufacturing complicated and high-maintenance internal combustion cars.

Paul Dietz said at December 9, 2006 7:27 AM:

Batteries would likely be more efficient, but there are other alternatives for stationary power, such as nuclear, that don't demand the sacrifice of so much land area. There will still be demand for liquid fuels, for example in long distance transporation or for backup fuel for PHEVs.

I suspect they could get many of the advantages promoted here by planting fields with several varieties of high yield engineered crops. The one that does best in the particular microconditions (soil, climate, etc.) will dominate. This used to be how grain was grown in some parts of Europe -- fields would be sown with a mixture of seeds, which would be harvested and ground to flour together.

Erich J. Knight said at December 10, 2006 6:42 PM:

I imagine the yield they get, as a result of plant diversity, is due concurrently with the micro flora and fauna diversity.

I'm going to post them about doing a Terra Preta soils plot.

A Better Biofuel?

"They then compared the biofuel energy yield when the plants were grown alone or in those different combinations. The most diverse plots produced 238 percent more bioenergy yield than the average plot containing a single species, says team leader David Tilman."

Terra Preta soil technology is a some what orphaned soil technology that speaks to so many different interests and disciplines that it has not been embraced fully by any. I'm sure you will see both the potential of this system and the convergence needed for it's implementation.

The integrated energy strategy offered by Terra Preta Soil technology may
provide the only path to sustain our agricultural and fossil fueled power
structure without climate degradation, other than nuclear power.

I feel we should push for this Terra Preta Soils CO2 sequestration strategy as not only a global warming remedy for the first world, but to solve fertilization and transport issues for the third world. This information needs to be shared with all the state programs.

The economics look good, and truly great if we had CO2 cap & trade in place:

These are processes where you can have your Bio-fuels, CO2 sequestration and fertility too.

'Terra Preta' soils I feel has great possibilities to revolutionize sustainable agriculture into a major CO2 sequestration strategy.
I thought, I first read about these soils in " Botany of Desire " or "Guns,Germs,&Steel" but I could not find reference to them. I finely found the reference in "1491", but I did not realize their potential .

Nature article:

Here's the Cornell page for an over view:

This Earth Science Forum thread on these soil contains further links, and has been viewed by 11,000 folks. ( I post everything I find on Amazon Dark Soils, ADS here):

The Georgia Inst. of Technology page:

There is an ecology going on in these soils that is not completely understood, and if replicated and applied at scale would have multiple benefits for farmers and environmentalist.

Terra Preta creates a terrestrial carbon reef at a microscopic level. These nanoscale structures provide safe haven to the microbes and fungus that facilitate fertile soil creation, while sequestering carbon for many hundred if not thousands of years. The combination of these two forms of sequestration would also increase the growth rate and natural sequestration effort of growing plants.

Also, Terra Preta was on the Agenda at this years world Soil Science Conference !

Here is a great article that high lights this pyrolysis process , ( ) which could use existing infrastructure to provide Charcoal sustainable Agriculture , Syn-Fuels, and a variation of this process would also work as well for H2 , Charcoal-Fertilizer, while sequestering CO2 from Coal fired plants to build soils at large scales , be sure to read the "See an initial analysis NEW" link of this technology to clean up Coal fired power plants.

Soil erosion, energy scarcity, excess greenhouse gas all answered through regenerative carbon management

The upcoming International Agrichar Initiative (IAI) conference to be held at Terrigal, NSW, Australia in 2007. ( )
If pre Columbian Indians could produce these soils up to 6 feet deep over 20% of the Amazon basin it seems that our energy and agricultural industries could also product them at scale.

Harnessing the work of this vast number of microbes and fungi changes the whole equation of EROEI for food and Bio fuels. I see this as the only sustainable agricultural strategy if we no longer have cheap fossil fuels for fertilizer.

We need this super community of wee beasties to work in concert with us by populating them into their proper Soil horizon Carbon Condos.

I feel Terra Preta soil technology is the greatest of Ironies.
That is: an invention of pre-Columbian American culture, destroyed by western disease, may well be the savior of industrial western society.


new_biochar_land said at February 6, 2011 10:04 AM:

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