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Biofuel crops may help achieve the goals of energy-efficient renewable ethanol production and greenhouse gas ( GHG) mitigation through carbon (C) storage. The objective of this study was to compare the aboveground biomass yields and soil organic C ( SOC) stocks under four crops (no-till corn, switchgrass, indiangrass, and willow) 7 years since establishment at three sites in Ohio to determine if high-yielding biofuel crops are also capable of high levels of C storage. Corn grain had the highest potential ethanol yields, with an average of more than 4100 L ha−1, and ethanol yields increased if both corn grain and stover were converted to biofuel, while willow had the lowest yields. The SOC concentration in soils under biofuels was generally unaffected by crop type; at one site, soil in the top 10 cm under willow contained nearly 13 Mg C ha−1 more SOC (or 29% more) than did soils under switchgrass or corn. Crop type affected SOC content of macroaggregates in the top 10 cm of soil, where macroaggregates in soil under corn had lower C, N and C : N ratios than those under perennial grasses or trees. Overall, the results suggest that no-till corn is capable of high ethanol yields and equivalent SOC stocks to 40 cm depth. Long-term monitoring and measurement of SOC stocks at depth are required to determine whether this trend remains. In addition, ecological, energy, and GHG assessments should be made to estimate the C footprint of each feedstock. [ABSTRACT FROM AUTHOR]

Biofuels from crops are emerging as a Jekyll & Hyde – promoted by some as a means to offset fossil fuel emissions, denigrated by others as lacking sustainability and taking land from food crops. It is frequently asserted that plants convert only 0.1% of solar energy into biomass, therefore requiring unacceptable amounts of land for production of fuel feedstocks. The C4 perennial grass Miscanthus× giganteus has proved a promising biomass crop in Europe, while switchgrass ( Panicum virgatum) has been tested at several locations in N. America. Here, replicated side-by-side trials of these two crops were established for the first time along a latitudinal gradient in Illinois. Over 3 years of trials, Miscanthus× giganteus achieved average annual conversion efficiencies into harvestable biomass of 1.0% (30 t ha−1) and a maximum of 2.0% (61 t ha−1), with minimal agricultural inputs. The regionally adapted switchgrass variety Cave-in-Rock achieved somewhat lower yields, averaging 10 t ha−1. Given that there has been little attempt to improve the agronomy and genetics of these grasses compared with the major grain crops, these efficiencies are the minimum of what may be achieved. At this 1.0% efficiency, 12 million hectares, or 9.3% of current US cropland, would be sufficient to provide 133 × 109 L of ethanol, enough to offset one-fifth of the current US gasoline use. In contrast, maize grain from the same area of land would only provide 49 × 109 L, while requiring much higher nitrogen and fossil energy inputs in its cultivation. [ABSTRACT FROM AUTHOR]