Panicum virgatum , known as switchgrass , is a perennial warm season bunchgrass native to North America, where it occurs naturally from 55 ° N latitude in Canada southwards to theUnited States and Mexico . Switchgrass is one of the dominant species of the North American tallgrass prairie and can be found in prairie grasslands , in native grass pastures , and naturalized along roadsides. It is used primarily for soil conservation ,production drilling , game cover, as anornamental grass , in phytoremediation projects, fiber, electricity, heat production, for biosequestration of atmospheric carbon dioxide , and more recently for a biomass crop for ethanol and butanol .
Other common names for switchgrass include tall panic grass, Wobsqua grass, blackbent, tall prairiegrass, wild redtop , thatchgrass, and Virginia switchgrass.
Description
Switchgrass is a hardy, deep-rooted, perennial rhizomatous grass that begins growth in late spring . It can grow up to 2.7 m high, but is shorter than big bluestem grass or indiangrass . The leaves are 30-90 cm long, with a prominent midrib. Switchgrass uses C 4 carbon fixation , giving it an advantage in conditions of drought and high temperature. [1] 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 grown from a single-flowered spikelet . Both glumes are present and well developed. When ripe, the seeds sometimes take on a pink gold 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 grow and harvest after annual harvesting. Once established, a switchgrass can survive for ten years or longer. [2] Unlike corn, switchgrass can grow on marginal lands and requires relatively modest levels of chemical fertilizers . [2] Overall, it is considered a resource-efficient, low-input crop for producing bioenergy from farmland.
Habitat
Much of North America, especially the prairies of the Midwestern United States, was rich in native swards, including switchgrass, indiangrass ( Sorghastrum nutans ), eastern gamagrass ( Tripsacum dactyloides ), big bluestem ( Andropogon gerardi ), little bluestem ( Schizachyrium scoparium ), bluestem grassland ( Andropogon panicum sorghastrum ) [3] and others. As European settlers Began spreading west across the continent, the native fat Were plowed under and the land converted to crops Such as corn , wheat , and oats. Introduced grasses such as fescue , bluegrass , and orchardgrass [4] also replaced the native fats for use as hay and pasture for cattle. [3]
Distribution
Switchgrass is a 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 is south of latitude 55 ° N from Saskatchewan to Nova Scotia , south of most of the United States east of the Rocky Mountains , and further south into Mexico . [5] As a warm-season perennialgrass, most of its growth; it becomes available and unproductive during colder months. Thus, the region may be affected, but in the southern reaches of its habitat, around the Gulf Coast area. [6]
Switchgrass is a diverse species, with striking differences between plants. This diversity, which presumably reflects evolution and adaptation to newer environments, has 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 more of northern origin, more cold-tolerant, and therefore generally preferred in northern areas. Upland switchgrass types are shorter (≤ 2.4 m, tall) and less coarse than lowland types. Lowland cultivars may grow to ≥ 2.7 m, in favorable environments. Both upland and lowland cultivars are deeply rooted (> 1.8 m, in favor soils) and have short rhizomes. The upland types tend to have more vigorous rhizomes, so 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, produce larger plants if they grow in size, and they tend to be more sensitive to moisture stress than upland cultivars. [7]
In native meadows, switchgrass is historically found in association with several other important native tallgrass prairie plants, such as big bluestem, indiangrass, little bluestem, grama sideoats , eastern gamagrass, and various forbs ( sunflowers , gayfeather , prairie clover , and prairie coneflower) . These hectares of tallgrass species occupied millions of hectares. [8]
Switchgrass’ suitability for cultivation in the Gran Chaco is being studied by Argentina’s Instituto Nacional de Tecnología Agropecuaria (INTA). [9]
Establishment and management
Switchgrass can be grown is regarded Unsuitable land for row crop production Including That land is too erodible for corn production as well as sandy and gravelly soils in humid areas Typically That Produce low yields of other farm crops. No single method of establishing switchgrass can be suggested for all situations. The crop can be established both by no-till and conventional tillage. When seeded as part of a mixture, planting guidelines for warm-season crops should be followed. Regional guidelines for growing and managing switchgrass for bioenergy or conservation plantings are available. Several key factors can increase the likelihood of success for establishing switchgrass. These include: [10]
- Planting switchgrass after the soil is well warmed during the spring.
- These seeds are highly germinable and planting 0.6 – 1.2 cm deep, or up to 2 cm deep in sandy soils.
- Packing or firming the soil both before and after seeding.
- Providing no fertilization at planting to minimize competition.
- Controlling weeds with chemical and / or cultural control methods.
Mowing and properly labeled herbicides are recommended for weed control . Chemical weed control can be used in the fall prior to establishment, or before or after planting. Weeds should be just growing up from the growing switchgrass. Hormone herbicides, such as 2,4-D , should be avoided as soon as possible. [11] Plantings that appear to be inferior in appearance are often incorrectly assessed. Switchgrass stands which are initially established in the future.[10] Once established, switchgrass can take up to three years to reach its full production potential. [12] Depending on the region, it is likely to produce 1/4 to 1/3 of its yield potential in its first year and 2/3 of its potential in the year after seeding. [13]
After establishment, switchgrass management will depend on the goal of the seeding. Historically, most switchgrass seedings have been managed for the Conservation Reserve Program in the US. Disturbance such as periodic mowing, burning, or disking is required to optimize the use of biodiversity . Increased attention is being placed on switchgrass management as an energy crop . Generally, the crop requires a modest application of nitrogen fertilizer, as it is not a heavy feeder. Typical nitrogen (N) glad of senescent material in the fall is 0.5% N Fertilizer nitrogen applications of about 5 kg N / hectare (ha) Applied For Each ton ofremoved biomass is a general guideline. More specific recommendations for fertilization are available regionally in North America . Herbicides are not often used on switchgrass after the seeding year, as the crop is very competitive with weeds. Most bioenergy conversion processes for switchgrass, including those for cellulosic ethanol and pellet fuel production, can generally be accepted as alternative species in the harvested biomass . Stands of switchgrass should be harnessed to more than one year, and one to one. Switchgrass can be harvested with la même field equipment used for hay production and it is well-suited tobaling or bulk field harvesting. If its biology is properly taken into consideration, switchgrass can offer great potential as an energy crop. [10] [14]
Uses
Switchgrass can be used as a feedstock for biomass energy production as ground cover for soil conservation , and to control erosion , for drilling and grazing , as game cover, and as feedstock for biodegradable plastics. It can be used by cattle farmers for hay and pasture and as a substitute for wheat straw in Many Applications, Including livestock bedding, straw bale housing, and as a substrate for growing mushrooms.
In addition, switchgrass is grown as a drought-resistant ornamental grass in average to wet soils and in full sun to part shade.
Bioenergy
Switchgrass has-been Researched have a renewable bioenergy crop since the mid-1980s, Because It is a native perennial warm season grass with the Ability to Produce moderate to high yields are marginal farmlands. It is now being considered for use in several bioenergy conversion processes, including cellulosic ethanol production, biogas , and direct combustion for thermal energy applications. The main agronomic advantages of switchgrass as a bioenergy crop are its stand longevity, drought and flooding tolerance, relatively low herbicide and fertilizerinput requirements, ease of management, hardiness in poor soil and climate conditions and adaptability Widespread in temperate climates. In some warm humid southern areas, such as Alabama , it has the ability to produce up to 25 oven-dry tons per hectare (ODT / ha). A summary of switchgrass yields across 13 research trial site in the United States found the top two cultivars in Each trial to yield 9.4 to 22.9 t / ha with an average yield of 14.6 ODT / ha. [15]However, these yields were recorded on small plot trials, and commercial field sites could be expected to be at least 20% lower than these results. In the United States, switchgrass yields appear to be highest in warm humid regions with the highest growth rates in the United States and the lowest in the Northern Great Plains . [15] The energy inputs required to grow switchgrass are favorable When Compared with annual seed bearing crops Such as corn , soybean , or canola , qui can require Relatively high energy inputs for field operations, crop drying, and fertilization. Whole plant herbaceous perennial C4grass feedstocks are desirable biomass energy feedstocks, as they require fewer fossils energy inputs to grow and effectively capture solar energy because of their photosynthetic system and perennial nature. One study quotes it takes from 0.97 to 1.34 GJ to produce 1 ton of switchgrass, compared with 1.99 to 2.66 GJ to produce 1 ton of corn. [16] Another study found that switchgrass uses 0.8 GJ / ODT of fossil energy compared to grain corn 2.9 GJ / ODT. [17] Given that switchgrass contains approximately 18.8 GJ / ODT of biomass, the energy output-to-input ratio for the crop can be up to 20: 1. [18] This highly favorable ratio is attributable to its relatively high energy output per hectare and low energy inputs for production.
Considerable effort is being expended in developing a variety of cellulosic ethanol crops in the USA. In George W. Bush’s 2006 State of the Union Address , he proposed using switchgrass for ethanol; [19] [20] [21] since then, over US $ 100 million has been invested in researching switchgrass as a potential biofuel source. [22] Switchgrass has the potential to produce up to 380 liters of ethanol per ton harvested. [23] However, current technology for herbaceous biomass conversion to ethanol is about 340 liters per ton. [24] In contrast, corn ethanol yields about 400 liters per tonne. [25]
The main advantage of using ethanol feedstock is that of grain corn, and more biomass energy per hectare can be captured in the field. [18] Thus, switchgrass cellulosic ethanol should give a higher yield of ethanol per hectare at lower cost. However, this will depend on the cost of constructing and operating cellulosic ethanol plants can be substantially reduced. The switchgrass ethanol industry energy balance is also substantially better than that of ethanol . During the bioconversion process, the lignin fraction of switchgrass can be burned to Provide Sufficient steamand electricity to operate the biorefinery . Studies have found that for each unit of energy input needed to create a biofuel from switchgrass, furnaces of energy are yielded. [26] In contrast, corn ethanol yields about 1.28 units of energy per unit of energy input. [27] A recent study from the Great Plains [28] indicates that for ethanol production from switchgrass, this figure is 6.4, or alternatively, that is more important in the ethanol production than in the switchgrass and converting it. to liquid fuel . However, there remain commercializationbarriers to the development of cellulosic ethanol technology. Projections in the early 1990s for the marketing of cellulosic ethanol by the year 2000 [29] have not been met. The commercialization of cellulosic ethanol is thus proving a significant challenge, despite noteworthy research efforts.
Historically, the major constraint to the development of greases for thermal energy applications has been the difficulty associated with burning fat in conventional combustion , as biomass quality problems can be of particular concern in combustion applications. These technical problems-have-been now to APPEAR Largely resolved through crop management practices Such As fall mowing and spring harvesting That allow for leaching to Occur, qui Leads to Fewer aerosol -forming compounds (Such As K and Cl) and N in the grass. This reduces clinker formation and corrosion, and enables a clean combustion fuel source for use in smaller combustion appliances. Fall harvested grasses may have more application for larger commercial and industrial boilers. [34] [35] [36] Switchgrass est being white used to heat small industrial and farm buildings in Germany and China through a process used to make a low quality natural gas substitute. [37]
Bai et al. (2010) Conducted a study to analyze the environmental sustainability of a switchgrass plant material as a feedstock for ethanol production. [38] Life cycle analysis was used to make this assessment. They compared efficiency of E10 , E85 , and ethanol with gasoline . They took into account the effects of growing, managing, processing and storing the switchgrass crop. They also made the switch to the ethanol plant where they assumed the distance was 20 km. The reductions in global warmingpotential by using E10 and E85 were 5 and 65%, respectively. Their models also suggest that the “human toxicity potential” and “eco-toxicity potential” were substantially greater for ethanol fuels (ie, E85 and ethanol) than for gasoline and E10.
In 2014, a genetically modified form of the bacterium Caldicellulosiruptor bescii was created which can cheaply and efficiently turn switch into ethanol. [39] [40]
Biodegradable plastics production
In a novel application, US scientists have genetically modified switchgrass to enable it to produce polyhydroxybutyrate , which accumulates in beadlike granules within the plant’s cells. [41] In preliminary tests, the dry weight of a plant has been shown to include up to 3.7% of the polymer. [42] Such low accumulation rates do not, as of 2009, allow for the use of switchgrass as a biosource.
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 – almost 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 switchgrass habitat have been beneficial, lending to the fertile farmland that exists today. The deep fibrous root systems of a deep-layered organic matter in the midwest, making those mollisolsoils 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, due to the grass root system.
Soil erosion , both of wind and water, is of great concern in areas where switchgrass grows. Due to its height, switchgrass can form an effective wind erosion barrier. [43] 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 switchgrass in their seed mixes when re-establishing growth along roadways. [44] It can also be used on minesites, dikes, [43] and pond dams. Conservation districts in many parts of the United States uses it for control of erosion in grass waterways because it provides habitat for wildlife.
Drilling and grazing
Switchgrass is an excellent drilling for cattle; However, it has been shown in the literature, by sheep and goats [45] [46] [47] through chemical compounds known as saponins , which causes photosensitivity and liver damage in these animals. Researchers are continuing to learn more about the specific conditions under which switchgrass causes harm to these species, but until more is discovered, it is recommended. 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 when the plants are about 50 cm tall, and that grazing be discontinued when the plants have been cut down to about 25 cm, and to rest the 30-45 days between grazing periods. [48] Switchgrass becomes stemmy and unpalatable as it matures, but during the target grazing period, it is a favorable drilling with a relative feed value(RFV) of 90-104. [49]The grass’s upright growth places on its stubble is important for its stem, so leaving 25 cm of stubble is important for regrowth. When harvesting switchgrass for hay, the first action occurs at the late boot stage – around mid-June. This should allow for a second cut in mid-August, leaving enough regrowth to survive the winter. [50]
Game cover
Switchgrass is well-known as a species of wild birds , such as pheasant , quail , grouse , and wild turkey , and song birds , with its plentiful small seeds and tall cover. A study published in 2015 has shown that switchgrass, when grown in a traditional monoculture, has an adverse impact on some wildlife. [51]Depending on how thickly it is grown, and what it is partnered with, it also offers excellent drilling and cover for other wildlife across the country. For those producers who have switchgrass stands on their farm, it is considered an environmental and aesthetic benefit to the abundance of wildlife by the switchgrass stands. Some members of Prairie Lands Bio-Products, Inc. in Iowa have turned this benefit into a profitable business by leasing their switchgrass land for hunting during the proper seasons. [52] The benefits to wildlife can be extended in large-scale agriculture through the process of harvesting, as recommended by The Wildlife Society, which suggests that rather than harvesting an entire field at once, the harvesting process could be practiced so that the entire habitat is not removed, thus protecting the wildlife inhabiting the switchgrass. [53]