Guest post: Cellulosic ethanol holds promise, but can we get it right?

UPDATED December 14, 2015.

This post was written by Loni Kemp, who has been a consultant to NRDC for seven years. She works on agriculture, energy and conservation policy for nonprofits, foundations and government. Previously she was at the Minnesota Project for 29 years. She is the author of the NRDC report, "Cellulosic Ethanol from Corn Stover: Can We Get It Right?"

The next ethanol boom is most likely to come from cellulose feedstocks, yet US policy is unprepared to ensure that harvest of annual crop residues is sustainable. That's the conclusion of a new report recently published by the Natural Resources Defense Council.

The drive toward truly sustainable and lower-carbon biofuels is a critical part of reducing fossil fuel use and greenhouse gas emissions from transportation. Corn ethanol began the transformation away from gasoline and now supplies about ten percent of the nation's gasoline, but it came at a high environmental cost to our soils and watersheds, and too often failed to deliver promised emissions reductions. Now, the next generation of non-food cellulosic feedstocks has the potential to take us much farther in reducing climate pollution and avoiding unintended impacts on our environment--but only if the feedstocks are managed sustainably.

The cellulosic revolution is being kicked off by corn stover, the residue of leaves, stalks and cobs left behind when corn is harvested. Stover is widely available where corn and ethanol are now produced, yet this abundant source of biomass has typically been left on farm fields to stop erosion and build soil quality. In other words, it is far from a "waste". Introducing stover harvest for biofuels therefore risks increasing carbon emissions, erosion, soil degradation, and water pollution.

Fortunately, our report finds that partial stover harvests, carefully calculated for flat and productive farm fields, can ensure that enough stover--half to three-fourths of what is produced--is retained on the field for essential soil protection. In combination with proven farming practices like no-tillage, crop rotations, and cover crops, partial stover harvests can be compatible with improving soils and increasing carbon capture in the soil. However, even partial stover harvest is not sustainable on many fields with slopes, marginal soils or where conventional tillage is practiced.

The report profiles the first three stover ethanol facilities, opened in the past year. We found that DuPont and Poet-DSM in Iowa, as well as Abengoa in Kansas, each took sustainability seriously and developed different yet potentially effective approaches and procedures to make sure that no more stover is harvested than is sustainable for each individual field. Poet-DSM uses a very conservative removal rate of only a quarter of the stover in any field, thus ensuring that the highly productive and flat cornbelt land around their facility will not degrade. Abengoa used detailed area recommendations developed by the USDA's Natural Resources Conservation Service (NRCS), using their well-vetted measurement tools, such as the Revised Universal Soil Loss Equation and the Soil Conditioning Index. DuPont, while more aggressive on stover removal, is going even further to develop individual farm plans over the next few years with detailed maps, specifying needed conservation practices and "no harvest" zones.

While much of this is good news, of concern is that at least one company is encouraging their farmers to eliminate crop rotations, even the minimal corn/soy rotation, and grow continuous corn year after year, utilizing stover harvest to reduce field work and increase profits. NRCS, on the other hand, promotes a broader view of soil health, encouraging farmers to build the biological life of the soil with crop rotations, significantly less tillage, and cover crops. These practices are far from widespread yet, and a rush to stover harvests and monoculture corn without requiring the needed conservation practices could lead to significant environmental impacts on the land.

Further, depending solely on corporate good will and voluntary sustainability schemes in a volatile industry is shaky. Just last week, Abengoa shut down their new cellulosic ethanol facility in Hugoton, KS, as well as their US headquarters and other facilities worldwide, as the Spanish corporation filed for bankruptcy filed for preliminary protection from creditors to manage debt. While the technology is working as hoped at the year-old plant, the global company's financial difficulties raise the question of when or if they will reopen the plant or possibly sell it. New owners would presumably be under no obligation to follow the carefully developed sustainability criteria that Abengoa developed.

So while the practices of the first three facilities are important and precedent-setting, especially to the extent they establish a high bar for the industry, they are not a substitute for strong public policies. Unfortunately, no policies are in place today to guide or regulate stover harvest, or ensure that future facilities take similar approaches.

Further, if the technologies employed by these leading companies prove viable and more facilities are built that rely on stover, the value of stover--and thus the value of growing corn--will increase, possibly contributing to demand for ever more corn production. Thus, the race is on not just to identify the best soil conservation practices and stover harvest management systems--and to make these mandatory--but to do so in a way that continues to be effective even as the scale of the market grows. This requires more than discouraging practices that would make an environmentally unsustainable farming system worse; it means actually encouraging changes in farming practices that are better for the land.

Beyond voluntary corporate standards, the report examines how the USDA and other agencies could be involved in ensuring sustainable stover harvest rates. We conclude that enforceable, site- specific conservation plans should be required, using NRCS standards; independent verification and monitoring of practices and resulting soil quality are necessary; and recommend that federal biomass subsidies be made contingent on company use of strict sustainability performance. If stover becomes a commodity with volumes bought on the open market, new policies must be created to ensure sources are being grown and harvested sustainably. Transparent reporting on the actual performance of the farms supplying a given facility across a broad spectrum of indicators would help limit the ability of facilities to compete with one another by over-collecting stover or otherwise encouraging poor management practices.

With good corporate examples available and a lull before cellulosic ethanol catches on broadly, now is the time to develop policies to ensure that biofuels from corn stover are done right.



About the Authors

Sasha Stashwick

Senior Advocate, Energy & Transportation and Food & Agriculture programs

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