The wide geographic distribution of switchgrass provides clear evidence of the species’ large genetic variation and broad adaptability. Indeed, this was a key attribute in the selection of switchgrass as a model species for energy production studies (McLaughlin and Kszos 2005; Wright and Turhollow

2010) . Within regions, switchgrass’ suitability to widely ranging edaphic and fertility environments is largely a function of ecotypic adaptation. Mesic, upland sites most often are occupied by upland ecotypes, which have lower sensitivity to moisture stress, whereas hydric bottomlands are the typical habitat for lowlands.

Although soils for these landscape positions may be quite distinct, soil type per se does not appear to have a particularly strong effect on switchgrass production (Sanderson et al. 1999). However, soil texture—and thus, soil water holding capacity—can have strong effects on switchgrass establishment and yield. Both excessively drained sandy soils and soils with poor internal drainage (as found on depositional sites—e. g., see Thelemann et al. (2010)) can limit switchgrass productivity.

Within the same soil type, slope may be a significant variable for switchgrass production. For example, Fike et al. (2006a) reported that yields on two sites with the same soil type differed by about 40% although the plots were only about 100 m apart. Aspect may also have played a role in these results as the higher yielding plots were more south facing. However, reductions in water infiltration and availability would be expected with increased slope.

Typical switchgrass production guides advise amending soil pH to 6.0 or higher for planting (e. g., Teel et al. 2003). However, switchgrass can tolerate a wide pH range (5-8) for germination (Hanson and Johnson 2005) and soil acidity is rarely a limiting factor for switchgrass in normal production settings. In fact, root growth at pH 3.7 was observed for switchgrass grown on a mine land reclamation site (Stucky et al. 1980). While reclaimed mine lands would be outside the typical boundaries for growing agronomic crops, switchgrass’ adaptability to harsh conditions, its tolerance of soil contaminants, and its capacity to grow on poorly structured soils makes it a useful crop for such difficult-to-crop sites.

Cultivar Selection

It may seem surprising—or even disconcerting—to note that as of this writing (2012), no registered cultivars specifically bred for biomass production have been released. But the reader should not be alarmed; switchgrass, relative to traditional row and forage crops, has been under investigation for only a relatively short period of time—and particularly so for bioenergy purposes. Historically, nearly all cultivars were selected for forage and conservation uses; only recently have registrations included descriptions of switchgrass cultivars as suited for bioenergy production. Such "multitasking" will likely be the norm for switchgrass for the foreseeable future, although these different purposes (forage and biofuels) require rather disparate management practices.

For any site, switchgrass cultivar selection should be driven by the need to match the plant materials to the extremes of the local growing conditions, regardless of end use. Adaptation to seasonal moisture regimes and temperature maxima and minima would be of primary consideration for choice of cultivars. With these factors in mind, we reconsider the value of moving switchgrass of "low-latitude" origin to greater latitudes. As we have noted above, such a strategy can increase yields by delaying inflorescence development, but this approach has bounds (and risks) because switchgrass needs adequate time to develop freeze resistance going into winter (Hope and McElroy 1990; Casler et al. 2004). Thus, moving low-latitude lines too far north (or to too high elevation) may be akin to imposing a death sentence on the crop. The general guideline of Moser and Vogel (1995) is to choose cultivars that are not more than 500 km from their latitude of origin, although we note exceptions where conditions are warmer than would be predicted based on latitude alone (e. g., Christian et al. 2001).