Switchgrass, a warm-season grass native to North America, has received much attention in recent years given its high yield potential, broad adaptability, and tolerance of marginal sites. The more robust lowland switchgrass ecotypes typically are preferred for bioenergy production systems given their greater yield potential, but lowlands have less cold tolerance, hence lower survivability, at greater latitude.

Switchgrass can be established both with conventional tillage and no-till planting systems. For either planting method, it is critical to have a clean, firm seedbed and to minimize weed competition after planting. Seeding depth is a critical issue for establishment, and can be greatly dependent on the firmness of the seedbed. Seed generally should not be planted more than about one centimeter deep for best establishment, although deeper plantings may be needed on drier sites.

Seeding rates as low as 1 kg ha-1 have been successful, but recommendations typically range from 4 to 8 kg ha-1. Seed often have high levels of dormancy, and this can cause stand failures in late-spring plantings if this is not accounted for. Several methods have been used to break dormancy successfully, but aging seed—holding for a year or so—may be the simplest method for doing so. Some have used planting timing to naturally break dormancy, and planting sometime from late fall to early spring can work well for this. Recommendations to this effect will be unlikely in regions where weed control issues are a challenge, however.

Switchgrass is known to benefit from mycorrhizal associations, and new research is showing a role for bacterial interactions that increase seedling growth. Many of the microbes produce plant-active hormones, and some may play a role in low N requirements due to biological N fixation. This is likely to be an important and growing realm of research in the future.

Little fertility is required for new switchgrass stands, and N as a general rule should not be applied in the year of seeding if the planting faces strong weed competition. Although mature, productive stands can benefit from N fertilization, input requirements will vary based on soils and harvest management, among other factors. As a rule of thumb, matching nutrient inputs to removal is likely to be closest to optimum in terms of meeting economic considerations and minimizing environmental impacts.

Weeds are a major issue in switchgrass establishment and there are very few herbicides currently labeled for use during switchgrass establishment. A number of herbicides have been evaluated in pre — and post-emerge applications to new seedings, and experimental results often vary by region —and even by switchgrass strain. For example, pre-emergence applications of atrazine have been successful in many cases but have been observed to harm certain lowland ecotypes. Safener treatments that protect seedlings from herbicide damage have proven less successful for switchgrass to date, but this work is ongoing.

One of the most successful ways to reduce weed problems at establishment is to plant switchgrass into the stubble of a glyphosate- resistant crop (especially soybeans) and follow good agronomic practices. Use of companion crops, grazing, mowing, or tillage may all provide some positive effect in controlling weeds—or at least, holding back the competition — in the establishment year. Once this first-year hurdle is overcome, there is typically little need for herbicides in established stands.

Diseases and insect pests may be a growing problem for switchgrass in the future as planted acres increase. The plant is host to a number of fungi, but pathogenicity is low for most species, and viral diseases may be an issue on the horizon. Accounts of yield reductions due to disease have increased in recent years, and breeding and selection for switchgrass as a biofuel crop needs to account for disease susceptibility to avoid potential disease vulnerability. Similarly, few insect pests have been a serious issue for switchgrass in the past, but several potential "species of interest" that could cause economic losses have been identified in recent years.

Harvest practices have potential to affect many parts of the supply chain in terms of fertility inputs, energy and CO2 balance, storage needs, and feedstock quality for processing. While most recommendations call for a single, end-of-season harvest, this may not account for the numerous feedbacks to the overall system. Although it makes great sense for minimizing costs on farm (i. e., by reducing nutrient losses), single, end-of — season harvests in a short harvest window may not account for the demands to the system in terms of meeting year-round processing needs. Rather, such a framework is likely to add to the equipment required to harvest, handle and move the material, as well as increase the demands for storage capacity. Thus, to be most effective, the development of switchgrass for biomass — to-bioenergy systems will need to consider the function of the system as a whole, and this is a different paradigm for much of agriculture.