Energy grasses as feedstock crops
Energy grass research
Energy grasses promise to be one of North Carolina's primary feedstocks for the state's biofuels industry sector. The Biofuels Center is trialling a number of energy grasses across the state in various soil types and with differing inputs to determine optimum practices and likely tonnages that can be obtained per acre. Additionally, the Center is working with industry to assist them in determining yields and tonnages on proprietary grasses. Some of the more promising energy grasses currently under consideration are listed below.
- Giant Miscanthus
- Arundo donax
- Sweet and biomass sorghums
A unique aspect of North Carolina's agricultural landscape is its hog sprayfield acreage. This irrigated, fertile land is largely contiguous and is currently being utilized by the hog industry for waste mitigation and presents an opportunity for biofuels producers to convert to energy grassland with very high yields. For more on this project, click on the Submenu top right.
Eastern North Carolina hog sprayfield acreage
North Carolina has one of the most densely farmed hog industries in the U.S., producing significant quantities of hog waste effluent in lagoons that is disposed of by spraying on grassland. The grassland, typically Coastal Bermuda, remediates the effluent and produces little value to the hog integrator. Uniquely, eastern North Carolina presents an opportunity for biofuels producers on these sprayfield acres in the pork-producing counties. Duplin, Sampson, and Wayne counties - all contiguous - retain nearly 100,000 acres of grassland to remediate nitrogen and phosphorous. The Biofuels Center is currently actively engaged in verifying the value for farmers and biofuels producers if new energy grasses were grown instead of Coastal Bermuda. With increased tonnages per acre, landowners can be profitable while still providing low-cost feedstocks to biofuels producers.
Giant Miscanthus is a perennial warm season grass in the sugarcane complex that has considerable potential as a biomass crop in North Carolina. Giant Miscanthus has been bred to be sexually sterile and propagates via asexual rhizomes.
Rhizomes are used to establish new stands and are planted in early spring. Some production will be realized the first growing season, but the main objective is to get the plants established for many years of production. During the second year, the plants will be in large clumps, and the canes grow to 12-15 feet in height. As temperatures cool in the fall, the dark green foliage fades to buff and drops, leaving the stems for harvest. Harvest is accomplished using commercially available hay harvesting equipment.
Giant Miscanthus is characterized as having broad adaptability, high water and fertilizer use efficiency, excellent pest resistance, and tremendous biomass production. Research by N.C. State University in partnership with the Center is underway to evaluate the performance of these crops across North Carolina, develop production practices and recommendations, breed and develop improved varieties, and improve efficiency of bio-processing and cellulosic ethanol conversion.
Tonnages of between 6-20 tons/acre are anticipated from miscanthus - or possibly more from sprayfield acreages - making it one of the highest yielding energy grasses tested in North Carolina so far.
Arundo donax is a tall perennial cane that is being researched as a potential biomass crop for cellulosic ethanol production in North Carolina. Literature indicates that Arundo donax can produce 20 dry tons per acre annually, making it one of the most productive of all energy biomass crops.
Arundo donax generally grows to 20 feet in height, with hollow stems 2 to 3 centimeters in diameter. It is an asexually reproducing species due to seed sterility. Stems and rhizomes are used to establish new strands and are planted in late winter/early spring, preferably in March. Arundo donax can also be propagated through the vegetative process of cutting mature canes in the fall and burying them in the ground.
Research is being conducted through the Biofuels Center of North Carolina to address concerns about the possible invasiveness of Arundo donax, in order to establish protocols to control and responsibly grow the crop.
To help determine the viability of Arundo donax as a potential energy crop that can replace Coastal Bermuda grass in the sprayfields of North Carolina, research is currently being conducted that examines the nitrogen intake levels of the plant. Other key questions being addressed concern large-scale production, processing, and profitability. The Biofuels Wiki has a video clip of Arundo donax having been used pre-World War II at industrial scale in Italy for fiber for the production of viscose, a fabric similar to polyester.
Switchgrass is a giant, warm-season perennial grass native to North America, that is high in cellulose, making it attractive as a biomass crop for cellulosic ethanol production in North Carolina. The tiny seeds are planted from late April to early June. Most of the first year’s photosynthate goes into root development in preparation for a long life span. Therefore, very little production should be expected the first year. In subsequent years, the switchgrass is harvested after the plants go dormant, usually after the first killing frost. Yield during the second year should be about 4 to 6 tons per acre and then averages 6 to possibly 10 tons per acre in subsequent years.
Adequate phosphorus and potassium levels in the soil are important for establishing switchgrass. However, annual maintenance application of fertilizer should be low to moderate. It is thought that since switchgrass is a perennial species, much of the nutrients in the foliage is translocated into the crown root system.
NC State University is conducting research on the agronomics of switchgrass at the Clayton research station and on the Williamsdale Farm near Wallace, North Carolina. The Biofuels Center has planted four varieties on the Oxford campus.
With a life span of 10 to 20 years, an average yield of 6 to 8 tons per acre, and low maintenance inputs, the economics of switchgrass production may be competitive with other crops in certain regions. With varietal improvement, switchgrass yields might approach 10 to 12 tons per acre per year.
Sweet and biomass sorghums
Sweet sorghum is a summer annual grass crop that has been grown in limited amounts in North Carolina for local molasses production. Sweet sorghum appears to present some opportunities for biofuels production:
- The aqueous sugar juice should be more easily converted into ethanol than cellulose
- Production inputs are thought to be less than that for corn
- Tonnages per acre are high
- North Carolina has grown sorghum in the past
- Sweet sorghum is drought-tolerant
To help determine the viability of sweet and biomass sorghum as an energy crop, the Biofuels Center has funded research at the Biofuels Campus and at other locations statewide. This research is focused on developing cost-effective methods to produce fermentable sugars from sorghums by addressing questions concerning large-scale production, processing, and storage.
One key question that needs to be addressed is the difference in the cost of growing sorghums, which are annual crops, relative to perennial energy grasses.