Abstract
The United States has mandated the production of 80 billion liters of second‐generation biofuel by 2022, and several approaches to meet this target focus on using ligno‐cellulosic ethanol from perennial grasses and non‐food crops. The large‐scale deployment of biofuel agronomy should consider high‐yielding crops that meet ethanol production goals, choose appropriate landscapes for biofuel crops from a climate and food production standpoint, and a full consideration of the environmental impact of large‐scale land use change. The southeastern United States has a long growing season conducive for producing high‐yielding crops, and is relatively less important to US food production than the rain‐fed Midwestern states that have been extensively studied for biofuel crops. We use the DayCent biogeochemical model to run simulation experiments to test the hypotheses that converting a large swath of traditional agriculture in the southeastern United States that is already utilized for bioenergy production (assuming 35% of current corn‐soy, and 10% of grazed pasture hectares; ~950,000 ha) to energy cane will result in greater biomass production, increased soil C storage, decreased soil N losses and lower greenhouse gas emissions than a landscape of corn‐soy rotations and interspersed grazed pasture. Our simulations suggest that energy cane above‐ground productivity on former pasture and corn‐soy fields would be between 52‐59 million Mg dry mass per year, resulting in 21.1–23.7 billion liters of ligno‐cellulosic ethanol, or ~28% of the 2022 US government mandate. DayCent did not predict significant changes in soil C flux from land conversion to energy cane, but simulations predicted lower rates of N loss compared to current agriculture. GHG emissions from energy cane landscapes were substantially higher on former pasture, but an order of magnitude lower when compared to corn‐soy hectares. While further study is needed to ascertain the full economic and industrial feasibility of converting nearly 1,000,000 ha of land to energy cane production, our results suggest that such an undertaking could meet a sizeable fraction of the US ethanol mandate, reduce N pollution and GHG emissions, and avoid compromising land devoted to food production in the southeastern United States.
Highlights
The Energy Independence and Security Act of 2007 commits the United States to produce 80 billion liters of advanced biofuel by 2022 (US Congress 2007)
There were approximately 50 billion liters of bio-ethanol produced in the United States in 2012 (United States Energy Information Administration 2012), but only ;40 million liters (,0.01%) came from second generation or advanced biofuels (Federal Register 2012)
Because rain-fed agriculture in the midwestern United States is important for both food production and bio-energy production, there is a concerted effort to understand the environmental impact of replacing corn with different biofuel crops (Heaton et al 2008, Davis et al 2010, 2012)
Summary
The Energy Independence and Security Act of 2007 commits the United States to produce 80 billion liters of advanced biofuel by 2022 (US Congress 2007). By definition, advanced biofuels are essentially any fuels not derived from plant sugars such as corn, sugar beet or sugar cane, and are instead formulated from biomass-derived ethanol converted from cellulose and lignin (Federal Register 2012). There is considerable uncertainty regarding what crops will be used as biomass feedstock and what landscapes will be converted to maximize energy crops’ potential to produce fuel. Most bio-ethanol produced in the United States is derived from corn grain (Zea maize; USDA Economic Research Service [USDA-ERS] 2012). Because rain-fed agriculture in the midwestern United States is important for both food production and bio-energy production, there is a concerted effort to understand the environmental impact of replacing corn with different biofuel crops (Heaton et al 2008, Davis et al 2010, 2012). An alternative is to expand biofuel crop production into regions that are less important to food production
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