|
|
|
|
Switchgrass
|
| |
|
| |
Panicum virgatum, commonly known as switchgrass, is a perennial warm season grass native to North America, where it occurs naturally from 55° N latitude in Canada southwards into the United States and Mexico. Switchgrass is one of the dominant species of the central North American tallgrass prairie and can be found in remnant prairies, in native grass pastures, and naturalized along roadsides. It is used primarily for soil conservation, forage production, game cover, as an ornamental grass, and more recently as a biomass crop for ethanol, fibre, electricity, and heat production.
Discussion
Ask a question about 'Switchgrass' Start a new discussion about 'Switchgrass' Answer questions from other users |
Recent Posts
Encyclopedia
Panicum virgatum, commonly known as switchgrass, is a perennial warm season grass native to North America, where it occurs naturally from 55° N latitude in Canada southwards into the United States and Mexico. Switchgrass is one of the dominant species of the central North American tallgrass prairie and can be found in remnant prairies, in native grass pastures, and naturalized along roadsides. It is used primarily for soil conservation, forage production, game cover, as an ornamental grass, and more recently as a biomass crop for ethanol, fibre, electricity, and heat production. Other common names for switchgrass include tall panic grass, Wobsqua grass, blackbent, tall prairiegrass, wild redtop and thatchgrass.
Properties
Switchgrass is a hardy, deep rooted, perennial rhizomatous grass that begins growth in late spring. It can grow up to 1.8-2.2 m high but is typically shorter than Big Bluestem grass or Indiangrass. The leaves are 30-90 cm long, with a prominent midrib. Switchgrass uses C4 carbon fixation, giving it an advantage in conditions of drought and high temperature. Its flowers have a well-developed panicle, often up to 60 cm long, and it bears a good crop of seeds. The seeds are 3-6 mm long and up to 1.5 mm wide, and are developed from a single-flowered spikelet. Both glumes are present and well developed. When ripe, the seeds sometimes take on a pink or dull-purple tinge, and turn golden brown with the foliage of the plant in the fall. Switchgrass is both a perennial and self-seeding crop, which means farmers do not have to plant and re-seed after annual harvesting. Once established, a switchgrass stand can survive for ten years or longer. Also, unlike corn, switchgrass can grow on marginal lands and requires relatively modest levels of chemical fertilizers. Overall, it is considered a resource-efficient, low-input crop for producing bioenergy from farmland.
Background
Much of North America, especially the prairies of the Midwestern United States, was once prime habitat to vast swaths of native grasses, including Switchgrass (Panicum virgatum), Indiangrass (Sorghastrum nutans), Eastern Gamagrass (Tripsacum dactyloides), Big Bluestem (Andropogon gerardii), Little Bluestem (Schizachyrium scoparium), and others. As European settlers began spreading west across the continent, the native grasses were plowed up and the land converted to growing crops such as corn, wheat, and oats. Introduced grasses such as fescue, bluegrass, and orchardgrass also replaced the native grasses for use as hay and pasture for cattle.
Distribution
Switchgrass is a very versatile and adaptable plant. It can grow and even thrive in many weather conditions, lengths of growing seasons, soil types, and land conditions. Its distribution spans south of latitude 55°N from Saskatchewan to Nova Scotia, south over most of the United States east of the Rocky Mountains, and further south into Mexico. As a warm season perennial grass, most of its growth occurs from late spring through early fall, becoming dormant and unproductive during colder months. Thus, the productive season in its northern habitat can be as short as three months, but in the southern reaches of its habitat, the growing season may be as long as eight months, around the Gulf Coast area.
Switchgrass is a diverse species, with striking differences between plants. This diversity, which presumably reflects evolution and adaptation to new environments as the species spread across the continent, provides a range of valuable traits for breeding programs. Switchgrass has two distinct forms, or "cytotypes": the lowland cultivars, which tend to produce more biomass, and the upland cultivars, which are generally of more northern origin, more cold tolerant, and therefore usually preferred in northern areas. Upland switchgrass types are generally shorter (= 8 ft, or 2.4 m, tall) and less coarse than lowland types. Lowland cultivars may grow to = 9 ft, or 2.7 m, in favorable environments. Both upland and lowland cultivars are deeply rooted (> 6 ft, or 1.8 m, in favorable soils) and have short rhizomes. The upland types tend to have more vigorous rhizomes. Subsequently, the lowland cultivars may appear to have a bunchgrass habit, while the upland types tend to be more sod forming. Lowland cultivars appear more plastic in their morphology, and produce larger plants if stands become thin or when planted in wide rows. On the other hand, lowland types seem to be more sensitive to moisture stress than upland cultivars.
In native prairies, switchgrass is historically found in association with several other important native tallgrass prairie plants, such as big bluestem, indiangrass, little bluestem, sideoats grama, eastern gamagrass, and various forbs (sunflowers, gayfeather, prairie clover, and prairie coneflower). These widely adapted tallgrass species once occupied millions of hectares.
Establishment
Once established, it takes three years for a stand of switchgrass to reach its full potential. According to David Bransby at Auburn University, it will produce a quarter to a third of its full potential in its first year and two-thirds in its second year. It is sometimes suggested that the stand not be harvested during the establishment year. Afterwards, each region has its own recommendations for fertilizer rates. The timing of harvesting depends upon how the switchgrass is to be used, and weed control can be addressed with limited herbicides, controlled burns, and mechanical methods.
Uses
Switchgrass is grazed by certain animals, used as ground cover to control erosion, and farmed as forage for beef cows. Switchgrass contains natural chemical compounds, called saponins, that may cause health problems to horses, goats, sheep and other livestock.
Switchgrass is rich in cellulose, making it attractive as a source for cellulosic ethanol. It is at the core of an alternative fuel strategy announced by Tennessee Governor Phil Bredesen in January 2007.
As a drought resistant ornamental grass, it is easily grown in average to wet soils and in full sun to part shade. Establishment is recommended in the spring, at the same time as corn is planted.
Soil conservation
Switchgrass is useful for soil conservation and amendment, particularly in the United States and Canada where switchgrass is endemic. Switchgrass has a deep fibrous root system – nearly as deep as the plant is tall. Since it, along with other native grasses and forbs, once covered the plains of the United States that are now the Corn Belt, the effects of the past switchgrass habitat has been beneficial, lending to the fertile farmland that exists today. The deep fibrous root systems of switchgrass left a very deep rich layer of organic matter in the soils of the midwest; making those mollisol soils some of the most productive in the world. By returning switchgrass and other perennial prairie grasses as an agricultural crop, many marginal soils may benefit from increased levels of organic material, permeability, and fertility from the grass's deep root system.
Soil erosion, both from wind and water, is of great concern in regions where switchgrass grows. Due to its height, switchgrass can form an effective wind erosion barrier. Its root system, also, is excellent for holding soil in place, which helps prevent erosion from flooding and runoff.
Some highway departments (for example, KDOT) have used switchgrasses in their seed mixes when re-establishing growth along roadways. It can also be used on strip mine sites, dikes, and pond dams. Conservation districts in many parts of the United States use it to control erosion in grass waterways because of its excellent ability to anchor soils while also doubling as native habitat for wildlife.
Game cover
Switchgrass is well-known among wildlife conservationists as a favorite forage and habitat among upland game bird species such as pheasant, quail, grouse, wild turkey, and song birds, with its plentiful small seeds and tall cover. Depending on how thickly switchgrass is planted, and what it is partnered with, it also offers excellent forage and cover for a wide variety of other wildlife across the country. For those producers who have switchgrass stands on their farm, it is considered an environmental and aesthetic benefit due to the abundance of wildlife attracted by the switchgrass stands. Some members of Prairie Lands Bio-Products, Inc. in Iowa have even turned this benefit into a profitable business by leasing their switchgrass land for hunting during the proper seasons. The benefits to wildlife can be extended even in large scale agriculture through the process of strip harvesting as recommended by the Wildlife Society, which suggests that rather than harvesting an entire fields at once, strip harvesting could be practiced so the entire habitat is not removed thereby protecting the wildlife that has inhabited the switchgrass.
Biofuel
Switchgrass is often considered a good candidate for biofuel — especially ethanol fuel — production due to its hardiness in poor soil and climate conditions, rapid growth and low fertilization and herbicide requirements. Switchgrass is also perennial, unlike corn, and has a large biomass output (the raw plant material used to make biofuel) of 6-10 tons per acre. U.S. President George W. Bush proposed the usage of switchgrass in his 2006 State of the Union address ; since then, over $100 million has been invested into researching switchgrass as a potential biofuel source.
Switchgrass has the potential for enough biomass to produce up to 100 gallons (380 liters) of ethanol per metric ton harvested. This gives switchgrass the potential to produce 1,000 gallons of ethanol per acre, compared to 665 gallons per acre of sugarcane and 400 gallons per acre of corn.
However, there is debate on the economic and environmental viability of switchgrass, and all other biofuels, as an efficient energy source. In recent studies, it has been argued that switchgrass has a negative ethanol fuel energy balance, requiring 45 percent more fossil energy to create switchgrass into a biofuel than is produced. Controversy has erupted over the Pimentel study, however, because of petroleum industry funding for his research. Also, some studies have countered his arguments, finding that for every unit of energy input to create a biofuel from switchgrass, four units of energy are yielded. In a 2007 lecture Professor Richard Muller, of the University of California, Berkeley, noted that it is the conversion of switchgrass biomass, mainly cellulose, into ethanol which introduces significant inefficiencies. It was also noted that The Helios Project at Lawrence Berkeley Laboratory is actively trying to engineer metabolic pathways in bacteria to convert cellulose to ethanol more efficiently.
Switchgrass is being used to heat small industrial and farm buildings in Germany and China through a process used to make a low quality natural gas substitute. It can also be pressed into fuel pellets which are burned in pellet stoves used to heat homes, which typically burn corn or wood pellets.
In the spring of 2008, of switchgrass will be planted near Guymon, Oklahoma, in the Oklahoma Panhandle to study the feasibility of using the crop for biofuel. It will be the largest stand ever planted for such purposes. The project is being spearheaded by the Oklahoma Bioenergy Center, a state project backed by Governor Brad Henry.
Forages
Switchgrass is an excellent forage for cattle; however, it has shown toxicity in horses, sheep and goats through chemical compounds known as saponins, which cause photosensitivity and liver damage in these animals. Researchers are continuing to learn more about the specific conditions under which the switchgrass must be in order to cause harm to these species, but until more is discovered, it is recommended that switchgrass not be fed to them. For cattle, however, it can be fed as hay, or grazed.
Grazing switchgrass calls for watchful management practices to ensure survival of the stand. It is recommended that grazing begin when there is 18 – 22 inches of growth, to stop grazing when there are 8 – 12 inches of stubble left, and to rest the pasture 30 – 45 days between grazing periods. Switchgrass becomes very stemmy and unpalatable as it matures, but during the target grazing period, it is a highly favorable forage with a relative feed value (RFV) of 90-104. The grass' upright growth pattern places its growing point off the soil surface onto its stem, so leaving 8 – 12 inches of stubble is important for regrowth. When harvesting switchgrass for hay, the first cutting occurs at the late boot stage – around mid-June. This should allow for a second cutting in mid-August, leaving enough regrowth to survive the winter.
Seed suppliers
See also
External links
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- - European Union study on Switchgrass feasibility.
- - Archive of Central Texas Plants
- - Has closeup photos of spikelets
- - General information repository on switch grass usage and feasible application as an alternative energy
- - Scientific American article on the potential use of switchgrass for biofuels
-
|
| |
|
|
