Switchgrass has substantial variation in many phenotypic and phenological traits that allow it to be adapted to a large portion of the U. S. (Casler et al. 2004; Casler et al. 2007). There are two distinct groups of switchgrass ecotypes: the lowland ecotypes, consisting of solely octaploids, and the upland ecotypes, consisting of both octaploids and tetraploids (Hultquist et al. 1996). Lowland ecotypes are generally adapted to more southern latitudes and upland ecotypes adapted to more northern latitudes (Casler et al. 2004). These ecotypes are also phenotypically distinct with lowland ecotypes often thriving in warmer climates, being taller, and having later anthesis occurrence resulting in longer growth periods (Cornelius and Johnston 1941; McMillan 1959). Whereas, upland ecotypes are generally more capable of surviving harsh late winter freezes (Vogel 2005). Within these two groups of ecotypes there are two subtypes, northern and southern, based on latitude of origin within each region (Casler et al. 2004).

Understanding the adaptation of switchgrass to variable growing conditions is key to determining its potential as a biofuel crop. The growth and development of switchgrass varies with climatic (i. e., temperature and precipitation) and environmental conditions (i. e., soil type, slope, nutrients) (Casler et al. 2004; Casler et al. 2007; Wullschleger et al. 2010). Field trials at relatively small scales (< 5 m2) and large scales (3-9 ha) reveal high biomass production, greater than 12 Mg ha-1 (Schmer et al. 2008; Wullschleger et al. 2010). Northern upland ecotypes flower earlier than southern upland ecotypes, causing reduced biomass production when moved south (Casler et al. 2004). On the other hand, southern lowland ecotypes flower later, which extends the growing season, resulting in increased biomass production when moved northward. However, survival of the lowland type is reduced in the North, which is thought to be due to cold winter temperatures (Casler and Boe 2003). The regional adaptation of switchgrass is complex but thought to be primarily reliant on genetic diversity for heat resistance, cold resistance, photoperiod, and drought tolerance (Casler et al. 2007). There is substantial genetic variation for many key adaptive traits, which may make it possible to enhance biomass production and decrease mortality.

The phenotypic diversity of switchgrass also makes the management practices that optimize yearly biomass yields vary by ecotype and location (Fike et al. 2006). Field trials have focused on identifying management practices (i. e., planting date, fertilizer application, irrigation, seeding rate, harvesting) required for establishment and optimum biomass production (Parrish and Fike 2005). As biofuel production expands globally, it is critical to also understand the environmental consequences of cultivating biofuel crops (Renewable Fuels Agency 2008). Large-scale production of biofuel crops, such as, switchgrass may bring both positive and negative environmental impacts. Some environmental benefits over traditional row crops include reduced water and wind erosion (Paine et al. 1996; McLaughlin and Walsh 1998; Jensen et al. 2007; Blanco-Canqui 2010). Additionally, decreased water runoff reduces the loss of agricultural chemicals, nutrients, and sediment into nearby waters, enhances nutrient cycling and storage, and recharges groundwater supply (Paine et al. 1996; Jensen et al. 2007; Blanco-Canqui 2010). Soils under long-term switchgrass production can also improve over time with increased soil organic matter production and the sequestration of SOC (Paine et al. 1996; McLaughlin and Walsh 1998; Tilman et al. 2006; Jensen et al. 2007; Blanco-Canqui 2010).

The environmental impact of bioenergy feedstock production systems will need to be closely monitored to ensure sustainability. Field scale monitoring is however limited in scope, temporally and spatially, and in most cases fails to fully account for the effects of site-specific conditions of management, land type, soil texture-hydrologic group interactions, slope, and climate. Therefore, many open-ended questions remain about the large — scale production potential of switchgrass and its long-term environmental impacts. For example: (1) Can switchgrass produce enough biomass to support local refineries and what regions of the U. S. will be used for large-scale feedstock production? (2) What are the optimal management practices for all potential field locations? (3) What is the long-term (i. e., 25 or 50 years) effect on soil quality and erosion? (4) How big of an impact will climate change have on switchgrass biomass production? Will lands that currently produce high levels of biomass be able to sustain these levels in the future?