Fuel from grasses could reduce carbon emissions with little impact on food supply

Biofuels are a hot debate topic. They can reduce petroleum-based transportation fuel use at the risk of diverting farmland for fuel production. Critics also argue that biofuels could increase carbon emissions depending on how they’re grown. But a new study finds that biofuels made from perennial grasses and other cellulosic biomass could meet U.S. renewable fuel goals with little impact on food production, all while reducing fossil fuel use and greenhouse gas emissions.

The study, published in the inaugural issue of the journal Nature Energy, is the first to combine ecosystem and economic models to assess whether cellulosic biofuel can reduce greenhouse gas emissions and meet the U.S. Environmental Protection Agency’s Renewable Fuel Standard (RFS).

The RFS sets an annual production target of 36 billion gallons of biofuel in 2022, of which at least 16 billion gallons were to be from cellulosic sources. Cellulosic source include non-food plants as well as non-food parts such as stems and leaves.

The study finds that biofuels from perennial grasses like switchgrass and miscanthus could meet a 32-billion-gallon target, with the rest coming potentially from waste sources. U.S. transport emissions in 2022 would decrease by 7 percent if the renewable standards were met using grass-based fuel. And if those fuels were given a production tax credit, corn ethanol could be phased out and greenhouse gas savings would nearly double to over 12 percent. The savings occur because gasoline is replaced and because grasses absorb carbon dioxide from air while growing, then store it in the soil.

According to Evan DeLucia, professor of plant biology at the University of Illinois at Urbana-Champaign who led the present study, perennial grasses have multiple advantages over corn for fuel. “Since both of those plants are perennial, you don’t till every year, so you release less carbon to the atmosphere,” he said in a press release. “The grasses also require less fertilizer, which is a source of nitrous oxide, and they store more carbon in the ground than corn.”

DeLucia and his colleagues used an ecosystem model that simulates the effects of climate and land-use change on carbon and nutrient cycling. They used the model’s outputs of biomass yield, soil carbon, and greenhouse gas balance as inputs to the economics model. Another input to the economic model is one of three different policy scenarios: no biofuel policy, RFS, and RFS including a tax credit. Based on these inputs, the economic model predicts land allocation and associated greenhouse gas emissions.

The RFS resulted in 3.9 million hectares of U.S. land converted to perennial grasses, mostly from grazing and idle land. The addition of the tax credit increased land under perennial grasses to 10 million hectares, with a reduction in corn ethanol land. Previous studies assumed that farmers would convert their most productive land to energy crops, whereas this study takes a more realistic approach with the inclusion of low-quality grazing and idle land. With both scenarios, the effect on food production land was negligible.

“Greenhouse gas savings from bioenergy have come under varying levels of attack, and this paper goes a long way to showing that contrary to what some are saying, these savings can be potentially large if cellulosic biofuels from dedicated energy crops meet a large share of the mandate,” DeLucia said. “This is a viable path forward to energy security, reducing greenhouse gases and providing a diversified crop portfolio for farmers in the U.S.” – Prachi Patel | 14 January 2016

Source: Tara W. Hudiburg, WeiWei Wang, Madhu Khanna, Stephen P. Long, Puneet Dwivedi, William J. Parton, Melannie Hartman & Evan H. DeLucia. Impacts of a 32-billion-gallon bioenergy landscape on land and fossil fuel use in the US, Nature Energy 1, (2016) doi:10.1038/nenergy.2015.5

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