John H. Fike, h* Twain J. Butler[3] [4] and Rob Mitchell[5]

Introduction

An intimate association with grasses has been important to human evolution (Cerling et al. 2011) and a key part of the subsequent rise of civilizations. Grasses historically have been a primary contributor to the human food supply—both directly, namely as sources of grains, and indirectly, as forages for livestock and wildlife. Grasses also have served an important and historical role in human transportation in as much they were the primary "fuel" for horses and the other beasts of burden used to move people and goods. This role changed substantially with the discovery of fossil fuels and the development of internal combustion engines.

There is, however, some promise that humanity will reengage with grasses as a source of fuels. As we look "back to the future" (Vogel 1996)—to avoid crises related to over-exploited fossil resources and the consequences of their combustion—grasses are reemerging as alternative sources of clean, renewable fuels. While grasses alone can by no means replace the more than 27,000 Exajoule (>26,000 trillion Btu) of fossil energy currently consumed in the US transportation sector (USEIA 2011), they can play an

important role in reducing our reliance on fossil energy sources and perhaps buy humanity some time in the search for more abundant sources of clean, renewable energy (Parrish and Fike 2005).

Among the many grasses and other crops explored for biomass — to-bioenergy systems, switchgrass has garnered some of the greatest attention for its potential as a biofuel feedstock. High productivity, broad adaptability and nativity to North America have all been important factors in the choice of switchgrass as a model energy crop. There have been important challenges associated with growing switchgrass, however, and in the remaining sections of the chapter, we will discuss the agronomic considerations and potential associated with its use as a bioenergy crop.