Switchgrass facts for kids
Quick facts for kids Switchgrass |
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| Conservation status | |
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| Genus: |
Panicum
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| Species: |
virgatum
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Switchgrass (scientific name: Panicum virgatum) is a type of grass that grows year after year, meaning it's a perennial plant. It's a "warm season" grass, which means it grows best when the weather is warm. Switchgrass is native to North America, growing naturally from Canada all the way down to the United States and Mexico.
This grass is a very important part of the tallgrass prairie in central North America. You can find it in leftover prairie areas, in fields where animals graze, and even growing naturally along roadsides. People use switchgrass for many things, like protecting soil, feeding animals, providing cover for wildlife, and as a pretty plant in gardens. It's also used in projects to clean up polluted soil and to make things like ethanol and butanol for energy.
Other common names for switchgrass include tall panic grass, Wobsqua grass, blackbent, tall prairiegrass, wild redtop, thatchgrass, and Virginia switchgrass.
Contents
What is Switchgrass?
Switchgrass is a strong grass with deep roots that grows back every year. It starts growing in late spring. This grass can grow quite tall, sometimes up to 2.7 meters (about 9 feet) high, but it's usually shorter than other tall prairie grasses like big bluestem.
Its leaves are long, about 30 to 90 centimeters (1 to 3 feet), and have a clear line down the middle. Switchgrass uses a special way to make its food called C4 carbon fixation. This helps it grow well even when it's dry and hot.
The flowers of switchgrass grow in a large cluster called a panicle, which can be up to 60 cm (2 feet) long. It produces many seeds, which are small (3–6 mm long). When the seeds are ready, they might look pink or dull purple, and in the fall, the whole plant turns a golden brown color.
One great thing about switchgrass is that it's a perennial and can reseed itself. This means farmers don't have to plant new seeds every year after harvesting. Once it's growing well, a switchgrass field can last for ten years or more! Unlike corn, switchgrass can grow on land that isn't perfect for other crops and doesn't need a lot of chemical fertilizers. It's considered a good plant for producing energy from farms because it doesn't need much care.
Where Does Switchgrass Grow?
Much of North America, especially the prairies in the central United States, used to be covered with huge areas of native grasses. This included switchgrass, indiangrass, eastern gamagrass, big bluestem, and little bluestem.
When European settlers moved west, they plowed up these native grasses. They turned the land into farms for crops like corn, wheat, and oats. Other grasses like fescue and bluegrass were also brought in to replace the native grasses for hay and cattle feed.
Switchgrass Across North America
Switchgrass is a very flexible plant that can grow in many different conditions. It can handle various weather types, different lengths of growing seasons, and many kinds of soil. Its natural range stretches from Saskatchewan to Nova Scotia in Canada, across most of the United States east of the Rocky Mountains, and south into Mexico.
Since it's a warm-season grass, most of its growth happens from late spring to early fall. It becomes sleepy and doesn't grow much during colder months. So, in the northern parts, it might only grow for three months. But in warmer southern areas, like near the Gulf Coast, it can grow for up to eight months!
Different Types of Switchgrass
Switchgrass is a diverse species, meaning there are noticeable differences between individual plants. This diversity helps the plant adapt to new places as it spreads. There are two main types:
- Lowland cultivars: These types usually produce more plant material (biomass). They can grow very tall, often over 2.7 meters (9 feet) in good conditions.
- Upland cultivars: These are usually from northern areas and can handle cold better. They are generally shorter (up to 2.4 meters or 8 feet) and less rough.
Both types have deep roots, often going more than 1.8 meters (6 feet) into the soil. They also have short underground stems called rhizomes. Upland types tend to have stronger rhizomes, which helps them spread more like a lawn. Lowland types might look more like they grow in clumps.
In its natural prairie home, switchgrass often grows with other important tallgrass prairie plants. These include big bluestem, indiangrass, little bluestem, sideoats grama, and various wildflowers like sunflowers and prairie clover. These tough prairie plants once covered millions of acres.
Scientists in Argentina are also studying if switchgrass can grow well in the Gran Chaco region.
Growing and Managing Switchgrass
Switchgrass can grow on land that isn't good for other crops. This includes land that easily washes away (erodes) or sandy and gravelly soils in humid areas. These types of land usually produce low amounts of other farm crops.
There isn't just one way to plant switchgrass. You can plant it without tilling the soil (no-till) or by using traditional tilling methods. If you plant it as part of a mix of grasses, follow the advice for planting warm-season grass mixes for conservation. Local guides are available for growing switchgrass for energy or conservation.
Here are some important tips for successfully planting switchgrass:
- Plant switchgrass in the spring after the soil has warmed up well.
- Use seeds that sprout easily. Plant them about 0.6 to 1.2 cm (0.25 to 0.5 inches) deep, or up to 2 cm (0.8 inches) deep in sandy soils.
- Press down or firm the soil both before and after planting the seeds.
- Don't use any fertilizer when planting. This helps reduce competition from weeds.
- Control weeds using chemicals or other methods.
Mowing and special weed killers (herbicides) are good for controlling weeds. You can use chemical weed control in the fall before planting, or before or after planting. When mowing weeds, cut them just above the height of the growing switchgrass. Avoid using certain hormone herbicides, like 2,4-D, early in the first year, as they can harm young switchgrass. Sometimes, a new switchgrass field might look like it's failing because of weeds, but it often gets established well in the next few years with proper care.
Once planted, switchgrass can take up to three years to grow to its full potential. In its first year, it might produce about a quarter to a third of what it eventually can. In the second year, it might produce two-thirds.
After it's established, how you manage switchgrass depends on why you planted it. For conservation, you might need to mow, burn, or disk the field sometimes. This helps keep the area good for different kinds of plants and animals.
When growing switchgrass for energy, it doesn't need a lot of nitrogen fertilizer. A general rule is to add about 5 kg of nitrogen for every tonne of plant material you remove. More specific advice for fertilizing is available in North America. Farmers usually don't use herbicides on switchgrass after the first year because the grass is very good at competing with weeds. Most ways of turning switchgrass into energy can handle a few other plant types mixed in with the harvested grass.
You should harvest switchgrass no more than twice a year. Often, one harvest gives as much plant material as two. You can harvest switchgrass using the same farm machines used for hay. It's easy to bale or collect in bulk. If managed correctly, switchgrass has great potential as an energy crop.
Uses of Switchgrass
Switchgrass is a very useful plant! It can be used as a raw material for making energy, as a ground cover to protect soil, and to stop soil from washing away. It's also used for animal feed, for animals to graze on, as cover for wildlife, and to make biodegradable plastics.
Cattle farmers can use it for hay and pasture. It can also replace wheat straw for things like animal bedding, building straw bale houses, and even for growing mushrooms.
Additionally, some types of switchgrass are grown as pretty plants in gardens. They are tough and can handle dry conditions, but they also grow well in average to wet soils and in sunny or partly shady spots.
Moth Host Plant
Switchgrass is a favorite plant for the caterpillars of the Dargida rubripennis moth. It's also a host plant for the caterpillars of the Delaware skipper and the Hobomok skipper butterflies.
Bioenergy
Scientists have been studying switchgrass as a renewable energy crop since the mid-1980s. This is because it's a native grass that grows year after year and can produce a lot of plant material on land that isn't good for other crops.
Now, people are looking at using switchgrass for several energy processes. These include making cellulosic ethanol, biogas, and burning it directly to create heat. The main benefits of switchgrass as an energy crop are that it lives a long time, can handle dry spells and floods, doesn't need many herbicides or fertilizers, is easy to manage, grows well in poor soil and climates, and can adapt to many temperate climates.
In some warm, humid southern areas, like Alabama, it can produce up to 25 dry tonnes of plant material per hectare. Studies in the United States show that the best types of switchgrass can yield 9.4 to 22.9 tonnes per hectare, with an average of 14.6 dry tonnes per hectare. However, these numbers come from small test plots, and larger farms might get about 20% less.
Switchgrass yields seem highest in warm, humid places with long growing seasons, like the southeastern U.S. They are lowest in dry, short-season areas of the Northern Great Plains. The energy needed to grow switchgrass is much less than for yearly crops like corn, soybeans, or canola. These other crops need a lot of energy for farm work, drying, and fertilizing.
Grasses like switchgrass are good for biomass energy because they need less fossil fuel energy to grow. They are also very good at capturing solar energy because of their special way of making food (C4 photosynthesis) and because they grow back every year. One study found it takes about 0.97 to 1.34 gigajoules (GJ) of energy to produce 1 tonne of switchgrass. This is much less than the 1.99 to 2.66 GJ needed for 1 tonne of corn. Another study found switchgrass uses 0.8 GJ of fossil energy per dry tonne, compared to corn's 2.9 GJ per dry tonne. Since switchgrass contains about 18.8 GJ of energy per dry tonne, the energy you get out compared to the energy you put in can be as high as 20 to 1! This great ratio is because it produces a lot of energy per hectare and doesn't need much energy to grow.
A lot of effort is going into making switchgrass a crop for cellulosic ethanol in the USA. In 2006, President George W. Bush suggested using switchgrass for ethanol. Since then, over US$100 million has been spent researching switchgrass as a possible biofuel source. Switchgrass has the potential to produce up to 380 liters of ethanol per tonne harvested. However, current technology gets about 340 liters per tonne. For comparison, corn ethanol yields about 400 liters per tonne.
The main benefit of using switchgrass instead of corn for ethanol is that it costs about half as much to produce. Also, more biomass energy can be collected from a hectare of switchgrass. So, switchgrass cellulosic ethanol should give more ethanol per hectare at a lower cost. But this depends on whether the cost of building and running cellulosic ethanol plants can be lowered a lot. The energy balance for switchgrass ethanol is also thought to be much better than for corn ethanol. During the process of turning switchgrass into biofuel, the woody part of the grass (lignin) can be burned. This creates enough steam and electricity to run the biofuel factory.
Studies have found that for every unit of energy put into making biofuel from switchgrass, four units of energy are produced. Corn ethanol, however, only yields about 1.28 units of energy for every unit put in. A recent study in the Great Plains showed that for switchgrass ethanol, this number is 6.4. This means the ethanol produced contained 540% more energy than was used to grow the switchgrass and turn it into liquid fuel.
However, there are still challenges to making cellulosic ethanol widely available. Predictions in the early 1990s that it would be ready by 2000 haven't come true. Making cellulosic ethanol a commercial success is proving to be a big challenge, even with a lot of research.
Using switchgrass for heat energy seems closer to becoming widespread than cellulosic ethanol. For example, switchgrass can be pressed into fuel pellets. These pellets can then be burned in special stoves that heat homes, similar to how corn or wood pellets are used. Switchgrass has also been tested a lot as a replacement for coal in power plants that make electricity. The Chariton Valley Project in Iowa is one of the most studied examples. The Show-Me-Energy Cooperative in Missouri uses switchgrass and other warm-season grasses, along with wood waste, to make pellets for a coal-fired power plant. In Eastern Canada, switchgrass is being tested on a small scale for commercial heating. Studies show it works well as a fuel for commercial boilers. Research is also being done to make switchgrass into pellet fuel because there isn't enough leftover wood in eastern Canada.
Generally, burning switchgrass directly for heat can give the most net energy and the best energy output-to-input ratio compared to other ways of turning switchgrass into energy. Research has found that switchgrass, when made into pellets and used as a solid fuel, is a good way to replace fossil fuels. Switchgrass pellets had an energy output-to-input ratio of 14.6 to 1. This is much better than for liquid biofuels made from farmland. As a way to reduce greenhouse gases, switchgrass pellets were found to be an effective way to use farmland to reduce greenhouse gases by about 7.6 to 13 tonnes of CO2 per hectare. In comparison, switchgrass cellulosic ethanol and corn ethanol reduced CO2 by 5.2 and 1.5 tonnes per hectare, respectively.
In the past, a big problem with using grasses for heat was that they were hard to burn in regular boilers. This was because of issues with the quality of the biomass. However, these technical problems seem to be mostly solved now. Farmers can manage the crop by harvesting it in the fall or spring. This allows certain compounds (like potassium and chlorine) and nitrogen to wash out of the grass. This reduces the formation of hard clumps (clinker) and corrosion, making switchgrass a clean fuel for smaller heaters. Fall-harvested grasses are probably better for larger commercial and industrial boilers. Switchgrass is also being used to heat small industrial and farm buildings in Germany and China. This is done through a process that makes a low-quality substitute for natural gas.
A study in 2010 looked at how environmentally friendly it is to use switchgrass for ethanol. They compared the efficiency of E10 fuel (10% ethanol), E85 (85% ethanol), and pure ethanol with gasoline. They considered air and water pollution from growing, managing, processing, and storing the switchgrass. They also included the transport of switchgrass to the ethanol plant. Using E10 and E85 reduced global warming potential by 5% and 65%, respectively. However, their models also suggested that the potential for "human toxicity" and "eco-toxicity" was much higher for fuels with a lot of ethanol (E85 and pure ethanol) compared to gasoline and E10.
In 2014, scientists created a special type of bacteria that can cheaply and efficiently turn switchgrass into ethanol.
Biodegradable Plastics
In a new use, US scientists have changed switchgrass genetically so it can produce a type of plastic called polyhydroxybutyrate. This plastic builds up in tiny beads inside the plant's cells. In early tests, up to 3.7% of the dry weight of the plant's leaves was this plastic. However, as of 2009, this amount was too low for switchgrass to be used commercially for plastic production.
Soil Conservation
Switchgrass is very helpful for protecting and improving soil, especially in the United States and Canada where it grows naturally. Switchgrass has a deep, strong root system, almost as deep as the plant is tall.
Since switchgrass and other native grasses once covered the plains of the United States (now the Corn Belt), they left behind a deep, rich layer of organic material in the soil. This made those soils some of the most fertile in the world today. By bringing back switchgrass and other perennial prairie grasses as farm crops, many poor soils can get more organic material, become more permeable, and gain fertility because of the grass's deep roots.
Soil erosion, caused by wind and water, is a big worry in areas where switchgrass grows. Because it's tall, switchgrass can form a good barrier against wind erosion. Its root system is also excellent at holding soil in place, which helps prevent erosion from floods and runoff.
Some highway departments, like the Kansas Department of Transportation, use switchgrass in their seed mixes when replanting along roads. It can also be used on old mining sites, dikes, and pond dams. Conservation groups in many parts of the United States use it to control erosion in grassy waterways. This is because it can anchor the soil while also providing a home for wildlife.
Forage and Grazing
Switchgrass is great food for cattle. However, it has been shown to be harmful to horses, sheep, and goats. It contains chemicals called saponins, which can cause skin sensitivity to sunlight and liver damage in these animals. Researchers are still learning more about the exact conditions under which switchgrass harms these species. Until more is known, it's best not to feed switchgrass to horses, sheep, or goats. For cattle, though, it can be fed as hay or grazed.
Grazing switchgrass needs careful management to make sure the grass field survives. It's suggested that grazing starts when the plants are about 50 cm (20 inches) tall. Grazing should stop when the plants have been eaten down to about 25 cm (10 inches). The pasture should then rest for 30 to 45 days between grazing periods. Switchgrass becomes tough and less tasty as it gets older. But during the right grazing time, it's good food for cattle.
When harvesting switchgrass for hay, the first cut happens in mid-June. This should allow for a second cut in mid-August, leaving enough grass to grow back and survive the winter.
Game Cover
Wildlife conservationists know that switchgrass is good food and a great home for upland game birds like pheasants, quail, grouse, and wild turkeys. It also helps songbirds, offering plenty of small seeds and tall cover. A study in 2015 showed that switchgrass, when grown alone in a large field, can sometimes negatively affect some wildlife. However, depending on how thickly it's planted and what other plants it's grown with, it can offer excellent food and cover for other wildlife across the country.
Farmers who have switchgrass fields on their land see it as a benefit for the environment and for its beauty. This is because many animals are attracted to switchgrass fields. Some farmers in Iowa have even made money by renting out their switchgrass land for hunting during the right seasons. The benefits for wildlife can even be extended in large-scale farming by using "strip harvesting." This means instead of harvesting an entire field at once, farmers harvest in strips. This way, the entire habitat isn't removed, which helps protect the wildlife living in the switchgrass.
Ornamental Cultivars
Different types of Panicum virgatum (switchgrass) are used as decorative plants in gardens and for landscaping. Some of these have won awards for their beauty, including:
- 'Dallas Blues'
- 'Heavy Metal'
- 'Hänse Harms'
- 'Northwind'
- 'Shenandoah'
Images for kids
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Panicum virgatum 'Heavy Metal', an ornamental switchgrass, in early summer
See also
In Spanish: Pasto varilla para niños
