NEW HOT PAPERS - 2008

 Why do you think your paper is highly cited?

There has been an astounding increase in interest in bioenergy and especially biofuels over the past three years. The public, decision makers, and researchers want to know about biofuel feedstocks other than just corn grain. Cellulosic feedstocks such as corn stover are considered to be very important future feedstocks but there hasn’t been much published research on their supply potential in a way that is quantitative or takes into account environmental constraints to their production or collection.

Our paper addressed the most readily available near–term source of cellulosic feedstock in the US—corn stover. The weight of a corn plant is half corn grain, half corn stover. Thus the US produces as much corn stover as corn grain and corn production occupies more agricultural land than any other crop and has for decades. We quantified the potential supply (cost and quantity) of this feedstock and we incorporated environmental and economic analysis into our assessment. We considered the range of soils and management approaches that are currently used to produce corn.

 Does it describe a new discovery, methodology, or synthesis of knowledge?

Our paper is a new rigorous assessment of an important potential supply of biomass which could be used to provide ethanol or other biofuels. We included economic, agronomic, and environmental considerations in a quantitative way.

 Would you summarize the significance of your paper in layman's terms?

If the US is to use biofuels to increase energy independence, corn stover (the remains of the corn plant after the grain is collected—i.e., stalk, leaves, cob) is an important potential source of biomass for those fuels. In growing corn for grain we produce millions of tons of corn stover every year. But leaving corn stover in the field is very important for reducing soil erosion and conserving soil carbon so we can't remove all the stover that is produced. Maintaining soil carbon and avoiding excessive erosion are important for maintaining the productivity of soils.

Taking into account the various soil types and corn crop management practices, we calculated at a county level how much stover could be collected in the US and still not cause serious erosion problems. The analysis was challenging because erosion is a function of weather, soil type, and how the crop is managed. We did not analyze how much stover should be left in the field to maintain soil carbon.

We also calculated the cost of collecting that stover into bales and found that most stover could be collected at a cost between $30 and $35 per dry baled ton. In our analysis we showed that if all corn crops were grown without tilling the soil we could collect almost twice as much corn stover without causing harmful levels of erosion.

Farmers can grow corn without tilling the soil and many do. If all corn was produced without tillage we could collect enough stover from our current corn crops to produce approximately eight billion gallons of ethanol. Currently in the US we produce six to seven billion gallons of ethanol annually from corn grain.

 How did you become involved in this research, and were there any problems along the way?

I am a systems ecologist interested in applied environmental problems. I would like to solve our energy challenges, but in a way that sustains the environment. It was challenging to model soil erosion as a function of stover removal across the thousands of soils on which corn is currently grown in the US and to marry economic, agronomic, and environmental information.

We would have liked to have quantitatively assessed the amount of corn stover that needed to remain in the field to preserve soil carbon but that is an even more complex problem and there were no soil carbon models we could easily adapt to assess the thousands of soil and corn crop management conditions that exist in the US.

 Where do you see your research leading in the future?

We would like continue the collaborations of ecologists, agronomists, agricultural engineers and economists working to discover ways to produce biomass feedstocks that are truly sustainable in an environmental, social, and economic sense. While we addressed erosion in this study in the context of corn stover removal for bioenergy, we are now researching soil carbon and water quality effects associated with the production of energy crops, specifically switchgrass. We are also expanding from a US-centric perspective to a global perspective.

 Do you foresee any social or political implications for your research?

If bioenergy is to be a useful technology it has to be environmentally, economically, and socially sustainable. Rigorous, transparent, peer–reviewable research that explores the intersection of all these elements is very important to developing a technology that truly meets the needs of the US. Our research points to the need to explore multiple cellulosic feedstocks and to tailor those feedstocks and their management to site-specific conditions. There will not be one feedstock that fits all conditions.

Robin L. Graham, Ph.D.
Groupleader, Energy & Environmental Systems Science
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, TN, USA

Keywords:  US corn stover supplies, bioenergy, biofuels, cellulosic feedstock, reducing soil erosion, conserving soil carbon, ethanol, corn grain, ecologists, agronomists, agricultural engineers, biomass feedstocks, switchgrass.