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Agricultural residues are important sources of feedstock for a cellulosic biofuels industry that is being developed to reduce greenhouse gas emissions and improve energy independence. While the US Midwest has been recognized as key to providing maize stover for meeting near-term cellulosic biofuel production goals, there is uncertainty that such feedstocks can produce biofuels that meet federal cellulosic standards. Here, we conducted extensive site-level calibration of the Environmental Policy Integrated Climate ( EPIC) terrestrial ecosystems model and applied the model at high spatial resolution across the US Midwest to improve estimates of the maximum production potential and greenhouse gas emissions expected from continuous maize residue-derived biofuels. A comparison of methodologies for calculating the soil carbon impacts of residue harvesting demonstrates the large impact of study duration, depth of soil considered, and inclusion of litter carbon in soil carbon change calculations on the estimated greenhouse gas intensity of maize stover-derived biofuels. Using the most representative methodology for assessing long-term residue harvesting impacts, we estimate that only 5.3 billion liters per year (bly) of ethanol, or 8.7% of the near-term US cellulosic biofuel demand, could be met under common no-till farming practices. However, appreciably more feedstock becomes available at modestly higher emissions levels, with potential for 89.0 bly of ethanol production meeting US advanced biofuel standards. Adjustments to management practices, such as adding cover crops to no-till management, will be required to produce sufficient quantities of residue meeting the greenhouse gas emission reduction standard for cellulosic biofuels. Considering the rapid increase in residue availability with modest relaxations in GHG reduction level, it is expected that management practices with modest benefits to soil carbon would allow considerable expansion of potential cellulosic biofuel production. [ABSTRACT FROM AUTHOR]

Abstract: Cellulosic biofuels face significant problems of feedstock aggregation and logistics leading to poor economies of scale. The current model is for relatively small biorefineries using feedstock gathered locally. Here a depot‐based decentralized biorefinery system is explored to estimate the US Energy Independence and Security Act (EISA) compliant corn stover ethanol production potential in the US Midwest. Depots serve to aggregate, pretreat, and densify biomass (via pellets) and thereby enable very large biorefineries using a decentralized system to collect these pellets. Such a corn‐stover based decentralized system using depots would establish one or two very large‐scale decentralized biorefineries capable of processing about 8–12% of the total corn stover available in the US Midwest. These decentralized biorefineries are economically competitive with the centralized biorefineries. About 55–153 depots could supply the pretreated pellets to the individual decentralized biorefineries leading to an annual production of 1.02–2.91 billion liters of cellulosic ethanol fuel. Most of the participating depots are located in Illinois and Iowa. The total EISA‐compliant ethanol fuel produced in the decentralized system is 2.82–4.07 billion liters per year. The ethanol selling price in the depot‐based decentralized biorefinery system varies between US$0.67 and US$0.72 L−1. The greenhouse gas (GHG) savings from cellulosic ethanol in the decentralized system compared to gasoline are 3.35–4.84 Tg CO2 year−1. Importantly, the total capital investment per annual volume of ethanol in the decentralized biorefinery ranges from US$0.71 L1 to US$1.15 L1, while the total capital investment per annual ethanol volume in the centralized biorefinery is US$1.98 L−1. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]