Land is the planet's limiting resource. We need land for food, biofuel, feed, ecosystem services, and more. But all land is not equal. Concerns about diverting land under food/feed crops to biofuel feedstocks have led to interest in using marginal land to produce these dedicated bioenergy crops for advanced biofuels. Marginal land has typically been defined as land that is of low quality and not in food crop production. Since energy crops can grow productively on low-quality land, there's great interest in the potential of energy crops on marginal land to avoid conflict with food production.

A recent study led by Chongya Jiang, a University of Illinois Research Scientist at the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), shows that researchers may be overestimating the amount of land that is available for bioenergy crops if they simply look at land that is low quality and low productivity. Results from this study by CABBI, a U.S. Department of Energy (DOE) Bioenergy Research Center, were published in Environmental Science and Technology.

"Sometimes that low productivity land will be in crop production if prices are high and at other times even high productivity land may be idle if crop prices are low," said co-author Madhu Khanna, the CABBI Sustainability Theme Leader and ACES Distinguished Professor in Environmental Economics at the University of Illinois Urbana-Champaign.

The research team applies the concept of economically marginal land as a preferable definition for land suitable and likely to be available for growing energy crops at low cost. They define economically marginal land as "land that is close to earning zero profits." Such land tends to be extremely susceptible to swinging in or out of crop production due to climate shock or economic shock. Farmers would potentially be willing to convert economically marginal land to energy cropland at low cost, as they're not losing much by converting it.

Estimating the amount of economically marginal land in the contiguous United States is no simple task, however. Widespread data on land profitability is not publicly available. So the CABBI team employed a clever solution to this problem: tracking changes in land use.

"This study presents a framework to assess marginal land by using frequent land use change as an indicator of economic marginality," Jiang said.

"We turned to satellite data," said co-author Kaiyu Guan, Blue Waters Associate Professor of Natural Resources and Environmental Sciences at Illinois. "Our team looked at which satellite pixels were permanently cropland, which were permanently grasslands, and which were frequently changing from one use to another. The pixels that were frequently changing are more likely candidates for economically marginal land."

It's not quite that simple, however. A change could simply be an error in classification, or there could be noise in the data, not a deliberate conversion from one form of land use to another. To deal with this, the team developed an algorithm using multi-source data as constraints that would allow them to identify where they were confident in classifying land, and where they were uncertain.

"We have processed 9 billion pixels for each of the 8 years of satellite data. It is a huge amount of work that only a supercomputer - the Blue Waters Supercomputer in our case - can enable us to do," Jiang said.

Historically, other studies have found anywhere from 43 million to 173 million hectares of marginal land in the United States. In contrast, the team identified 10 million hectares of land that could be classified as economically marginal with confidence. Of those 10 million hectares, 1.4 million to 2.2 million hectares are in the rainfed region suitable for bioenergy crop production, and not currently under crop production.

In another recent collaboration, results of which were published in Global Change Biology - Bioenergy, Khanna, Jiang, Guan, and co-authors from the Great Lakes Bioenergy Research Center (GLBRC) and the Center for Bioenergy Innovation (CBI), fellow DOE Bioenergy Research Centers, took their pursuit of refining the definition of marginal land a step further.

Economically marginal land is based on market returns, but this definition of marginal land fails to capture the environmental impacts associated with different types of land use. It's well known that land in crop production tends to generate a variety of negative environmental impacts, such as nitrogen runoff and soil carbon depletion.

"There may be some land that is profitable but that is producing negative environmental effects that are not priced," Khanna said. "If we were to price those social and societal costs, the land would not be profitable. When considering if land is marginal, we should consider all these negative externalities associated with food crops, as well as the beneficial ecosystem services that come from land used for natural forests and natural grasslands. We not only want to avoid conflict with food production, but also ensure we are improving the environment."

Applying this social marginality framework to real-world land use will require an interdisciplinary approach. Site-specific monetization of the benefits along with ecosystem models could assess which areas are causing the most environmental damage and which areas could have the greatest benefits if converted. And then combining that with their understanding of economically marginal land, researchers could pinpoint areas where land might be economically beneficial but socially marginal.

All these methods are still evolving and need further research to be precise and accurate, but Khanna hopes that implementing the team's social marginality framework will provide both a mechanism for greater collaboration across the Bioenergy Research Centers and a solid foundation to build up our understanding of which land is most suitable for growing energy crops.

Research Report: "Assessing Marginal Land Availability Based on Land Use Change Information in the Contiguous United States"

Related Links
Institute For Sustainability, Energy, And Environment
Bio Fuel Technology and Application News

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