Seed dormancy and slow seedling development often have been contributing factors to poor switchgrass establishment (Zarnstorff et al. 1994). Switchgrass seed display high levels of dormancy immediately following harvest (Knapp 2000; Madakadze et al. 2000; Teel et al. 2003). Sautter (1962) reported that seeds tested within 33 d of harvest were only 10% germinable, and rates approaching 5% are not uncommon (Parish and Fike 2005).

Dormancy is a natural mechanism that serves to prevent premature seed germination, and ultimately, seedling death. Under natural conditions, switchgrass seed will not germinate until stratified—i. e., until exposed to a period of cool, moist conditions as occur during late fall to early spring. Stratification can be imposed artificially (Zhang and Maun 1989; Beckman et al. 1993; Zarnstorff et al. 1994; Haynes et al.1997; Shen et al. 1999; Wolf and Fiske 2009) by allowing seed to imbibe moisture and keeping chilled for several weeks, and a similar process is used in seed testing methods. Herein lies the potential problem surrounding the planting of switchgrass based on a seed tag’s statement of PLS. Under official testing methods, seeds are exposed to a period of moist chilling before immediately incubating at appropriate germination temperatures (AOSA 1993). The conditions for seed testing often can break dormancy; with highly dormant seed lots, this could mask the low level of germination that would occur when they are planted in the field.

When sowing switchgrass, particularly in late spring, it is important to know the level of dormancy in a seed lot because planting rates should be based on the amount of germinable seed, not simply on PLS percentages.

We use the "late spring" qualifier, because some producers and researchers have had success with late fall/early spring plantings that break dormancy by allowing the seed to naturally stratify, and we discuss planting timing strategies in a subsequent section.

Several methods to artificially break dormancy have been explored, including after-ripening, stratification, seed priming, acid or mechanical scarification, and hormonal treatments (Jensen and Boe 1991; Beckman et al. 1993; Zarnstorff et al. 1994; Haynes et al. 1997; Shen et al. 1999; Madakadze et al. 2000; George 2009; Ghimire et al. 2009). These techniques work with various degrees of success—and success can vary by cultivar and growing conditions, among other factors. We note here, too, that any effective seed priming or dormancy abatement technique must face the greater question of whether it can be practically applied at a commercial scale.

Seed priming, an osmotic process in which seeds are hydrated to a level where metabolic activity begins but radicle emergence does not occur, may enhance switchgrass germination (Beckman et al. 1993). Some chemical treatments such as hydrogen peroxide treatment can increase seed germination and emergence and provide more uniform seedling development for non-dormant seeds (Sarath et al. 2006). Karrikinolide [3-methyl-2H-furo[2,3-c]pyran-2-one], a compound isolated from smoke that promotes germination and seedling establishment in several native species did not increase switchgrass germination or seedling vigor (George

2009) . Some biological agents such as mycorrhizae and bacteria are also known to benefit switchgrass germination and seedling vigor, but their role in breaking dormancy is, unexplored. This topic will be discussed in the section on switchgrass fertilization.

One of the simplest methods for reducing dormancy is merely to hold the seed at moderate temperatures for an adequate period of time. Holding seed at 23°C for 90 to 180 d is adequate for overcoming most short-term seed dormancy (Zarnstorff 1994). Elevated storage temperatures also can break dormancy and can reduce the storage time required for after-ripening (Shen et al. 1999). Both of these after-ripening techniques must be managed carefully, however, as aging, and especially accelerated aging (with heat) can reduce seed viability (Zarnstorff et al. 1994; Shen et al. 1999).

As a production issue affecting establishment success, dormancy may be beginning to fade in importance for growers. Some seed purveyors already market pretreated, ready-to-plant seed that do not require additional stratification or after-ripening. Dormancy also may be eliminated altogether as switchgrass use increases, because low-dormancy switchgrass lines could become standard for cultivars of the future. Sanderson et al. (1996) reported that by collecting and growing plants from non-dormant, neoteric (newly harvested) seeds, dormancy rates could be significantly reduced. Similarly, Burson et al. (2009), also have selected plants from non-dormant neoteric seeds for subsequent breeding and improvement. The advances made from these efforts suggest that dormancy-related stand failures could soon be a thing of the past and may simply be one of the birthing pains associated with bringing to market a new crop with a short history of plant improvement.