Biomass Feedstocks

Biofuel Feedstock – Switchgrass

There is an increasing interest in sustainable biomass feedstock production worldwide due to the high cost and diminishing availability of petroleum-based fuels. Additionally, the concern over global warming caused by fossil fuels has quickened the pace of research into low cost biofuels that have significantly reduced greenhouse gas emissions and can compete with fossil fuels. The dedicated crop production of biomass feedstocks is becoming a new and fast-paced, agricultural industry.

Switchgrass Cellulosic Ethanol

Switchgrass (Panicum virgatum) can be used as a biofuel feedstock in the production of cellulosic ethanol, but it has also been identified as a promising feedstock for pelletized biofuels. The direct combustion of these pellets provides energy for heating, and the pellets can be combusted with coal to reduce greenhouse gas emissions. Other high-fiber grasses such as Big Bluestem (Andropogon gerardii) and Indiangrass (Sorghastrum nutans) may also be promising biomass feedstocks for pelletized fuels.

Applewood Seed Company carries a number of different Switchgrass varieties that are suitable for biomass feedstock production. There are two ecological variants of Switchgrass: upland and lowland. The lowland types are robust, grow very tall and have more rapid growth whereas the upland types are more slender, shorter and slower growing. Our upland or intermediate varieties include Cave-in-Rock, Blackwell, Dacotah, NE 28, Sunburst, and Trailblazer. Our lowland varieties are Alamo and Kanlow. See Table 1 and the planting range maps below for more information about these varieties.

Comparative Advantages of Switchgrass As a Biomass Feedstock

Switchgrass Photo 1

Switchgrass

  • Switchgrass is a perennial, herbaceous crop and does not have to be replanted every year. This reduces the costs associated with annual cropping.
  • There is reduced carbon loss from the soil since it is not plowed annually. Every time a field is plowed, carbon is released to the atmosphere. Carbon stays sequestered in the soil for as long as 20 years in a field of switchgrass.
  • Switchgrass can be grown on marginal or degraded land which is not used for food production.
  • Switchgrass has a high pest resistance and is tolerant to flood and drought.
  • Switchgrass has low fertilizer and water requirements.
  • Switchgrass has numerous ecological benefits.

Switchgrass: Description and Uses

Switchgrass is a warm-season, perennial grass that is native to the United States. Its range covers the area from the eastern edge of the Rockies to the Atlantic coast, extending north into Canada. It was commonly found associated with other tallgrass prairie plants such as Big Bluestem, Indiangrass, Little Bluestem, Gayfeather and Prairie Coneflower. It is a bunchgrass, growing in clumps rather than spreading like a sod grass, and it tends to have very deep roots. Switchgrass has several ecological uses, which include prairie restoration, soil conservation, water quality improvement, and wildlife forage and habitat. It is also used in pastures and for hay crop production.

Biomass Switchgrass Cultural Information

Switchgrass is broadly adapted and can tolerate a wide range of soil types. Loam is ideal for biomass production, but Switchgrass is suitable for growing in marginal land because of its low moisture and fertilizer requirements. The soil pH should fall in the range of 5 to 8, with 6.5 being ideal. Because it is a warm-season grass, the air temperature must be 75-85°F (soil temp. at least 60°F) for germination to occur.

Moisture is essential for initial germination and establishment. The soil should remain moist for at least one month during this period. Once established, water is not so critical. In arid climates, upland varieties are more suitable because they can survive on less water than lowland varieties.

There are 3 methods for successfully establishing Switchgrass: Conventional tilling and drill planting, no-till planting, and frost seeding. Because Switchgrass seed is very small, the soil should be smooth and firm prior to sowing. For biomass energy crop production, use 4-10 pounds per acre, seeded at a depth of ¼ to ½ inch. If drilling in rows, consult your local county extension agent for recommendations on row width and planting rate for your region.

When using the no-till method, the drill should have a roller or press-wheel to insure that there is good seed to soil contact. This method works best when seeding into crop stubble or an area that previously had existing vegetation that has been sprayed with a general herbicide and mowed or scalped. The bed should be very smooth and have at least 50% bare soil showing.

Frost-seeding involves broadcasting seeds in the early spring freeze-thaw period. The action of freezing and thawing of the soil helps to work the seed down into the soil. This method is useful if the seed has high dormancy because the seed is cold stratified and has better germination. This method works best when the field is bare or at least has some exposed soil. It is not recommended if there is the potential for competition from perennial, cool-season grasses or weeds.

The establishment of warm-season Switchgrass can be difficult because of competition from weeds. Weeds can be controlled during the first season by the use of nurse crops or mowing 2-3 times during the growing season. Typical nurse crops include sorghum-sudangrass, spring planted wheat and triticale. Annual weeds grow much faster than the Switchgrass seedlings and can be removed easily by mowing. Be sure to mow prior to any weed seed set, and mow to just above the height of the Switchgrass. Perennial weeds can be reduced by mowing because it depletes the root reserves and significantly weakens these weeds.

After stand establishment, broadleaf weeds can be controlled with a broadleaf herbicide that has been approved for use on warm season grasses. Cool season grasses can also be sprayed with herbicide in the spring when the Switchgrass is dormant.

Little or no fertilization is recommended for Switchgrass feedstock production. High quality ethanol feedstock should have very low nitrogen content because nitrogen reduces the conversion efficiency and contributes to air pollution after combustion.

Switchgrass varieties should be chosen based upon the ecotype (upland or lowland) and the latitude of origin. Refer to Table 1 for general descriptions of Switchgrass varieties that we sell. The maps indicate the planting range for each variety. Please note where ranges overlap, the lowland varieties will generally out-yield the upland varieties.

Table 1 Switchgrass Varieties from Applewood Seed Company
Variety
Ecotype
Maximum
Height (In.)
Seed Origin Latitude Minimum Annual Precipitation Needed* Maturity
* For adequate biomass production, provide supplemental irrigation if natural precipitation is inadequate in your area
Alamo
Lowland
120″ (300 cm)
TX
29°
25″ (64 cm)
Late
Blackwell
Upland
50″ (125 cm)
OK
37°
20″ (50 cm)
Mid
Cave-In-Rock
Intermediate
60″ (150 cm)
IL
38°
25″ (64 cm)
Mid-late
Dacotah
Upland
60″ (150 cm)
ND
46°
20″ (50 cm)
Early
Kanlow
Lowland
100″ (250 cm)
OK
35°
30″ (76 cm)
Mid
NE 28
Upland
60″(150 cm)
NE
42°
20″ (50 cm)
Mid
Sunburst
Upland
75″ (188 cm)
SD
43°
20″ (50 cm)
Early
Trailblazer
Upland
60″ (150 cm)
NE
40°
20″ (50 cm)
Mid

Planting Ranges for Switchgrass Varieties

Switchgrass Fuel Pellets

Switchgrass can be densified into biomass pellets for use in coal fired electrical plants, industrial boilers, and cellulosic biomass pellet stoves. The greenhouse gas emissions from Switchgrass pellets are up to 90% lower than those from petroleum-based fuels, and the amount of carbon dioxide released into the air by the combustion of the pellets is reclaimed in the process of Switchgrass production.

To make the pellets, Switchgrass is first harvested in late fall with conventional haying equipment. The grass biomass is then chopped and ground by special equipment and run through a pellet press, which will remove air and tightly compress the grass particles. The extruded pellets are then cut into smaller pieces for easy handling. For home heating use, Switchgrass pellets require special grass pellet stoves because their burn qualities are different from wood and cannot be burned in conventional wood pellet stoves.

Biomass Ethanol Feedstock: Polycultures

A Switchgrass field is a monoculture because it is planted to one species of plant, and polycultures are fields with 2 or more species of plants. Biomass energy research is being done on diverse mixtures of grassland perennials as feedstocks for direct combustion. These low-input, high-diversity (LIHD) polycultures may be more efficient than Switchgrass alone and have certain ecological advantages over monocultures. There is continuing research on polyculture feedstocks as a direct combustion fuel. They may become very useful as a biofuel, especially if used to supply energy for cellulosic ethanol plants. There will be a growing market for this renewable form of energy as a replacement for fossil fuels.

LIHD Polycultures Versus Monocultures

Polycultures of Grasses and Forbers Photo

Polyculture of grasses and forbs.

  • Native hay meadows are already in existence and are good exambles of LIHD polycultures. They are a traditional form of land management.
  • LIHD mixtures have greater bioenergy yields than monocultures grown on fertile soils, including Switchgrass.
  • They have low water, pesticide and fertilizer requirements. In fact, soil fertility is built up with diverse native plant systems, especially if nitrogen-fixing legumes that contribute nitrogen to the soil are included in the mixture.
  • They help to maintain high biological diversity and provide a natural balance.
  • They provide food and habitat to wildlife, including pollinators such as native bees and butterflies. Pollinator conservation is a hot topic due to concern over diminishing native populations and the Colony Collapse Disorder that has devastated honey bees in recent years. Pollinators are essential to the agricultural industry and are vital components of a healthy ecosystem.
  • Native species are already adapted to the local environment and do not need further selection for adaptive traits.
  • Complete crop failures are less likely with mixtures of species, and they are less susceptible to disease and pest problems.
  • They can be produced on marginal or degraded land which is not used for food production.
  • They can provide hay for livestock.
  • LIHD biofuels are carbon negative.

Definitions, Background and Science

Cultural, Production and Management Information