Outlook: The Negligible Benefits of Food-Based Biofuels

David Tilman
Experimental and Mathematical Ecologist, University of Minnesota
Monday, March 26, 2007; 11:00 AM

David Tilman, an experimental and mathematical ecologist at the University of Minnesota, was online Monday, March 26, at 11 a.m. ET to talk about the Sunday Outlook article he wrote with applied economics researcher Jason Hill, which examines the pitfalls of food product-based biofuels -- and the promise hidden in the nation's prairies.

Corn Can't Solve Our Problem (Post, March 25)

The transcript follows.


David Tilman: Hi Everyone,

We are delighted that you could join us today. Lets get our discussion on the road.

Dave Tilman and Jason Hill


Washington: Dr. Tilman -- read your papers, they are a great contribution to our knowledge on this fast-moving topic. As you know, some corn growers have suggested taking acres out of the Conservation Reserve Program (CRP) to grow fuel. No doubt growing mixed grasses would be a better idea than corn, but even so, I thought the idea of paying farmers not to grow anything on this acreage was to get some environmental benefit, or at least not to do more harm to environmentally sensitive land. Are you saying that the growing (and repeated harvesting) of grasses would not have a negative effect on land in the CRP now?

David Tilman: CRP lands do give large environmental benefits. These benefits can be maintained, or even increased, if these lands are properly harvested for biofuel. It will be crucially important that lands be harvested in ways that do not harm wildlife. Research on this shows harvest should be in the late fall, and be done with equipment that scares away wildlife before cutting.

If these lands were planted to diverse native species, this would be a major environmental plus.


Annandale, Va.: Very interesting article. Question: How suitable are the native prairie plants you experimented with for the new biofuel conversion processes (such as enzymatic) being developed for waste agricultural materials and/or switchgrass?

David Tilman: There is more work to be done on ethanol via enzymatic digestion and fermentation, but it seems that the prairie plants, including mixtures of species, can be a good feedstock.


Manassas, Va.: I own a diesel vehicle that achieves an average of 45 mpg. What is stopping exploration of bio-diesel with a combination of hybrid technology to achieve 100 or more mpg with increased performance? Thanks for taking my question.

David Tilman: I talked with engineers with Ford and Daimler about this, and their companies are pursuing this full force. It has great potential.


Arlington, Va.: I have to say, all of this seems like a desperate attempt to maintain an unsustainable way of life rather than face up to changes that actually would help alleviate the problem. We are here trying to replace a fuel (so called fossil fuels) that is the product of millions of years of stored and concentrated sun energy; we think we can do this by growing, harvesting and processing a single growing season's worth of sun energy on a continuous basis? Energy cannot be created nor destroyed, correct? All the energy found in plant material comes from the sun -- or if any comes from terra firma, it must be replaced to keep the process going, correct? Not to mention the water needed to ensure good crop yields, which is becoming a scarce resource as well. Corn, sugarcane, wild prairie grasses, it makes no difference -- there is no free lunch. Try living somewhere where you can walk to work and your kids can walk to school, and forget about burning things just to move around.

David Tilman: We agree with you that lifestyle changes will be a big part of solving our energy and climate change issues.

Also, for any fuel, we need to determine the net energy we gain -- the difference between output and fossil inputs. The gain, of course, ultimately comes from the sun, via plant photosynthesis.


Aspen, Colo.: When considering buying a new car with the underlying aim of lowering ones carbon output/footprint, is it smarter to look at a hybrid/fuel cell, or an FFV capable of E-85?

David Tilman: Hybrids are the best. E85 is not a good use of limited ethanol stocks. If we had a second generation form of ethanol, such as from prairie grasses, E85 would make good environmental sense.


Fairfax, Va.: Is CRP land suitable for "prairie hay" and not for corn, or might the biofuel folks in fact be able to put some of that land back into corn production as they seem to want to do? In either case, would you please comment on the effect on wetlands and further on down the environmental line if the CRP lands currently set aside are returned to use? Thank you.

David Tilman: Some CRP lands are suitable for corn. With the price of corn as high as it is, farmers, like anyone else, will be tempted to return to corn.

This would have serious environmental impacts because many CRP acres are specifically set aside to protect wetlands and water quality.


Arlington, Va.: Fantastic article. Although food-based biofuel is not the correct long-term solution, couldn't it be an intermediate step of many in moving away from oil? I could see a scenario in which food-based ethanol is used for the next 10-15 years, then the non-food based ethanol is merged in as the process becomes more efficient until we achieve the proper balance.

David Tilman: This is the scenario that we hope will occur, although we hope that the transition can be much faster -- perhaps within the next five years.

Also, corn ethanol can be much better energetically and for its greenhouse benefits if prairie biomass is used to provide all the energy needed to convert corn to ethanol.


Beltsville, Md.: I am concerned about the long-term sustainability of the conventionally-grown crops necessary to produce food-based biofuels. I feel that we are substituting one set of problems for another to maintain our levels of energy consumption.

David Tilman: The biggest issue for sustainability of corn is that it requires immense inputs of agrichemicals and energy. There are many better alternatives for energy crops that don't need such inputs.


Kensington, Md.: In your article, it did not seem to me that you adequately factored in the extremely high cost of procuring fossil fuels that are made into gasoline -- not just that acquiring coal or oil leaves environmental destruction in its wake, but that the barriers to entry are enormous. You need geological surveys, negotiations for mining or drilling rights, etc. (and I don't mention the destruction of life and civilization that also can accompany trying to acquire fossil fuels -- think of Germany's invading Romania for its oil fields, or the alleged ulterior motives of our country in the Middle East). Once you have all that, the capital outlays are enormous to get started, and the occupational risk to your workers is insanely high -- and after the fact you are left with huge unrecoverable costs. I literally can get my own micro-refinery making biodiesel going in under a year, and I don't need to blow up mountains or chop down any trees to do it. Because biofuels can be microproduced locally, transport costs are negligible compared to fossil fuels. Let me ask you, did you factor that in?

I also don't understand how world hunger can be exacerbated by biofuel production -- it's a distributional, not a quantity issue. Perhaps more of those huge ships that formerly were moving oil around can be employed to move food around better. As to the power needed to produce biofuels: First, why would the tractors not run on biofuel? Second, the leftover plant matter can be burned and generate more than enough power for a refinery -- this is carbon-neutral. There is a sugar plant in Hawaii that does just that -- the leftover sugar cane is burned and is able to produce more electricity than the factory uses, and the leftover power is sold back into the grid (it once provided 100 percent of the power for local residents). The system at this factory has been in place I believe for about a century. I think you should work a bit harder to come up with a general-equilibrium assessment. I suspect you would find many of your arguments undermined.

David Tilman: Long question -- short answer.

The world has a limited amount of fertile land. Land used for biofuel cannot be used to grow food.

Global demand for both food and energy will double in about 40 years. There were already serious concerns about where we'd get the land needed just for food. Biofuels could easily demand even more land than that.

It's a big issue, no easy answers, but no doubt that biofuels and food will strongly compete unless we only grow biofuels on marginal lands.


Washington: As a "veteran" of the U.S. biofuels industry, I read with some trepidation your piece in yesterday's Washington Post. Your basic point about corn-based ethanol is reasonably accurate, especially how much ethanol we can expect can be produced from corn without creating other economic problems (about 12 billion gallons/year, which we'll achieve in the next two years or so). No responsible person in this industry believes that corn is the be-all or end-all for the future of ethanol; rather, it is just the start after 30 years of development. Other energy crops and feedstocks you describe, as well as municipal solid waste, et al, must be developed if we are to achieve goals like 25 percent displacement of our petroleum consumption by 2025 (see It is vitally important, too, that the U.S. commit to serious energy conservation and substantially improved fuel efficiencies if biofuels are to make a dent in our energy security and global climate-change challenges. Would you please comment on these matters?

David Tilman: Current biofuels are a start in the right direction. We examined them to find out how to do better.

Goals, such as 25 percent renewable by 2025, are wonderful -- but we need to be fully honest about them by carefully determining the full energy and environmental costs and benefits. We must not "forget" to subtract the fossil energy used to make a "renewable" biofuel.

Our energy security will be helped, to some extent by biofuels. Conservation and efficiency will play a much bigger role. Foreign policy is also important.


Jason Hill: This is Jason Hill joining the discussion. Thank you for the invitation to speak with you today.


Fairfax, Va.: Your analysis shows that corn is not the best solution to reduce carbon emissions -- but the financial incentives for farmers and the ethanol industry clearly favor corn production. What would it take for high-density prairie grass to become a realistic alternative?

David Tilman: If the subsidies and mandates for biofuels were based on their energy and environmental benefits, prairie biofuels would be economically competitive. Right now the economic benefits of corn ethanol come from the federal VEET subsidy of $0.51/gallon and from state laws that mandate that gasoline can only be sold if it is blended with a certain percent ethanol.

A blending mandate that specified that the blended fuel have a 10% lower greenhouse gas impact than gasoline would immediately favor fuels with better results.


Accokeek, Md.: Why does the greenhouse gas benefit of growing mixed prairie grasses on degraded farm land last only for a century?

David Tilman: Prairie plants created the carbon rich and fertile soils of the Midwest. They will recreate these soils if planted on a degraded site. However, after about 100 years, the soil will be brought back to its former level of soil carbon and fertility. At that point, the inputs of carbon from plants will be balanced by the rate of carbon decomposition by soil bacteria, fungi and other decomposers.


Washington: Do you believe that biofuel demand will cause a growth in genetically engineering the plant material that is used to make ethanol, or the bacteria that are used to convert the plants into fuel?

Jason Hill: Researchers are exploring both options. There is interest both in biofuel feedstocks that more easily are converted into biofuels as well as in the enzymes/bacteria that are used to perform this conversion. Nevertheless, it is possible that such gains may not even come close to matching the 238 percent gain in biomass production we saw provided by the natural benefit of biodiversity.


Columbia, Md.: The enzymatic approach has been around for decades -- what makes it better now than the thermal biomass processes?

David Tilman: Right now the most efficient way to convert biomass into a transportation fuel is via gasification. This process can create ethanol, synthetic diesel, or synthetic gasoline. It also can produce electricity. Moreover, the CO2 released can be captured and stored in old oil wells or other geological formation.

Enzymatic processes likely require a smaller capital outlay, and also should have increased efficiency as they progress. However, gasification is proven technology that offers many benefits. It definitely deserves much more attention than it has been getting recently.

In the long term, each has its own benefits -- suggesting that these two technologies can coexist and each contribute to providing renewable and environment-friendly energy.


Bethesda, MD: Dr. Tilman, I've enjoyed reading your papers over the years. You mentioned that in Brazil they burn the remainder of the sugar cane plants to power the ethanol stills. Other than the air pollution problems, is there any reason why they couldn't use the cornstalks instead of oil products to distill corn ethanol?

David Tilman: There are two currently unanswered questions about this matter. First, corn stalks add carbon back to the soil. If they are burned, soil carbon levels will fall, harming soil fertility and increasing the levels of atmospheric greenhouse gasses. Second, corn stalks form a soil surface mulch that help prevent soil erosion, which is a critical part of sustainable agriculture.

As things stand, I think it unwise to remove the stalks and use them for energy.


Frederick, Md.: Because photosynthesis has only a 0.5 percent to 1 percent energy conversion, would it make more sense to cover the land with solar PV cells that have a 15 percent to 20 percent energy conversion, with minimal ecological damage?

Jason Hill: We have not done life cycle analyses on solar energy, but your question highlights the importance of looking at the entire life cycles of different methods of energy "production" when choosing among various alternatives. Answering this question would require us to look at the net energy output from these two systems, the net greenhouse gas and pollution emissions, the economic competitiveness of each scenario, and other such factors. For instance, for the greenhouse gas balance of each scenario we would need to know how much GHG are released when producing the bioenergy, how much GHG are avoided by displacing fossil fuels, and how much GHG are either released or sequestered in the land these systems cover.


New Orleans, La.: Would growing high-density hay keep the wetlands of the northern plains intact? These wetlands are vital to maintaining the duck populations of North America.

David Tilman: High-diversity prairie hay fields, if properly located on the landscape, would protect wetlands and their wildlife.


Arlington, Va.: Hi Dave -- thanks for bringing this to the attention of society. In terms of cellulosic ethanol, what proportion of nonarable lands in the U.S. conceivably could be converted to biomass production, and what what reduction in fossil fuel use could that engender? My guess is that conversion of all nonarable lands would only make a small dent in fossil fuel consumption. And could you address the consequences of such a broad-scale conversion?

David Tilman: I don't know the acreage of all nonarable lands in the US. Our proposal is that biofuel production be restricted to lands that have already been farmed and have now been set aside or other such lands, such as roadsides and power line rights of way. These lands can give us much more energy that using all of our corn for ethanol. Planting these lands with energy-yielding diverse mixtures of native species gives us energy, removes and stores CO2, and provide habitat for native species. However, if we were to use our remaining undisturbed native ecosystems for bioenergy, we'd lose all of these benefits.


Washington: I have 320 acres in North Dakota that I would like to plant with this grass. Where can I get information on types of grasses and seed distributors?

Jason Hill: A healthy prairie has more than just grasses in it. It also has forbs/wildflowers that contribute to its total biomass production, wildlife benefit, and aesthetic beauty. Nitrogen-fixing legumes are especially important to a healthy, productive prairie as they make this important nutrient available to the grasses and other plants. The key to all of this is diversity.

A quick Web search for such keywords as "prairie," "native," "seed" and "restoration" should reveal many stores that not only sell seed but also have experience in restoring prairie lands. You should also contact the Nature Conservancy or your state natural resources group to find out which species are native to your area. Those would be the best ones to plant.


Ijamsville, Md.: While sugarcane in the U.S. is a marginal proposition except for in small parts of Florida, would bioethanol made from sugar grown in Haiti or the Dominican Republic make ecological and economic sense in terms of energy payback and global warming? If so, wouldn't this help alleviate our energy dependence on the Middle East and help some of our poorer neighbors?

David Tilman: I don't know the particulars of cane production in these nations. Based on other analyses of sugarcane ethanol, ethanol from these regions would likely be an excellent biofuel, as long as it is grown on existing land and processed efficiently. This would offer these poor nations a profitable business, and provide the US with a valuable fuel. It seems like a win-win.


Oslo, Norway: Would any action be more effective than planting forests in the northern parts of the taiga and Canada as these thaws up in the summertime? In Far North, Peril and Promise: Great Forests Hold Fateful Role in Climate Change (Post, Feb. 22)

David Tilman: Northern boreal forests capture and store large amounts of atmospheric carbon, as does tundra. Management that accelerated the succession to these ecosystem types would have greenhouse benefits.


Vienna, Va.: Dr. Tilman, who funded your research? Is there adequate funding for you and others to address the big remaining questions in this environment-energy-food equation?

David Tilman: The National Science Foundation has provided us with critically important funding that has allowed us to do fundamental work on biological diversity and how it impacts the functioning of ecosystems. None of this would have happened without NSF. Our work on biofuels was a direct application of those results. NSF supports basic research, but also encourages its researchers to go the next step by communicating it with public and applying it.

We also have been funded by the State of Minnesota's Initiative on Renewable Energy and the Environment.


Madison, Wis.: Can ethanol refineries utilize any source of biomass, or would existing refineries need to be retrofitted to process prairie hay?

Jason Hill: Existing corn ethanol refineries could use biomass in one of two ways, both of which offer tremendous environmental and energy benefits. First, the biomass could be combusted to provide the heat and electricity to convert corn to ethanol. This would greatly offset fossil fuel use (natural gas and coal). Second, biomass could not only be used as the energy source but also the raw material feedstock for ethanol production, displacing corn itself. Essentially, the cellulose in biomass could be broken down into sugars to be fermented, and the other portion of the biomass, the lignin, could be combusted to provide the heat and electricity to perform this conversion. Both ways of using biomass would require modification of existing facilities.


Arlington, Va.: With regard to lifestyle changes, wouldn't changing to a vegetarian or mostly vegetarian diet have significant impact on greenhouse gases? Your article mentions that it takes three pounds of corn to produce one pound of chicken, or eight pounds of corn for a pound of beef. By using the corn to feed people directly, you use significantly less land and energy.

Jason Hill: Yes, it most certainly could. Either going completely vegetarian or even reducing meat consumption could have positive greenhouse gas benefits for many reasons including reducing native ecosystem destruction and not needing to burning as much fossil and even renewable fuels to produce our food.


Raleigh, N.C.: What a great discussion topic. Given your experience in this area, what end-uses and specific biofuels do you think will be major players in Minnesota and the Great Lakes region in the near-term (next five to ten years). For example, do you think that a majority of the biodiesel produced or switchgrass harvested will be predominantly used for vehicles, co-fired or combusted or gasified in the electricity sector, combusted/gasified in the industrial (non-electricity) sectors or used in the commercial/residential sectors? Your thoughts here are appreciated.

David Tilman: Co-combusting coal and biomass would help reduce CO2 emissions associated with electric power generation, which is a major source of CO2 release here and around the world. This purpose, alone, could use an immense amount of biomass. Gasifying biomass, or gasifying biomass with coal and capturing and storing the CO2 would allow production of transportation biofuels that offered great energy and environmental benefits. Home heating with pellet stoves that burned pelletized prairie grasses is another way that offers great benefits. Using prairie biomass to provide the energy needed to run corn ethanol plants also improves the energy and environmental benefits of the resulting ethanol.


Rockville, Md.:"However, gasification is proven technology that offers many benefits." Some sort of an article that explains this would help. One would like to know the "benefits."

David Tilman: Right now, at least, gasification is more energy efficient. A higher percent of the energy in the biomass can be captured in transportation fuels and electricity than for the other processes. The 'waste' CO2 from a gasifier can then be captured and stored in the ground, which is another benefit.


Arlington, Va.: How much maintenance or "gardening" do diverse mixtures of prairie species require in order to keep them in a highly productive state and to avoid invasion/conversion by exotic species?

David Tilman: At our site, essentially no maintenance was needed for the high-diversity plots. We have some plots that we planted to 32 species in 1994, that have never been weeded or otherwise maintained (no pesticides or herbicides, etc.) since 1996, and that provide high energy yields. In contrast, all of our monoculture plots were invaded by other species, and it took great effort to keep them just one species.


David Tilman: Hi Everyone,

Thanks for the excellent questions. We are signing out.

All the best,

Dave Tilman and Jason Hill


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