Switchgrass is a giant, warm-season perennial grass native to North America that is high in cellulose, making it a potential candidate as a biomass crop for cellulosic ethanol production in North Carolina. It is a hardy, warm-season perennial that can grow 6 to 7 feet in height.

Research shows that switchgrass improves soil quality, provides habitat for native species, limits soil erosion and filters nutrients and contaminants. It can also serve as a buffer to existing annual crops—such as corn, soybeans and wheat—by reducing pest invasion and agricultural run-off, and limiting the need for chemical applications.

Researchers at the Ecological Society of America estimate there are approximately 51 to 67 million hectares of available U.S. land that could be used for native perennial crops; those areas could produce as much as 321 million tons of biomass per year².

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. As a consequence, switchgrass yields are negligible in the first year. In subsequent years, 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 8 tons per acre. "Back-of-the-napkin" calculations show that a 50 million GPY ethanol facility would need about 15 football fields of baled switchgrass daily to meet production requirements.

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 of North Carolina has planted four varieties on the Biofuels Campus in Oxford.

With a life span of 10 to 20 years, an average yield of 6 to 8 tons per acre, low management costs, and low maintenance inputs, the economics of switchgrass production appear competitive with other energy crops. With varietal improvement, switchgrass yields might approach 10 to 12 tons per acre per year. Also, this feedstock is inedible; thereby, posing no threat to food supplies.

Quick Facts
* The net energy output of switchgrass is about 20 times better than corn's.^citation?
* Results of a recent USDA-ARS study showed that the average overall production cost across 5 production years was about $68.56 per metric ton. The researchers concluded that “substantial quantities of switchgrass could have been produced in the region at about $50 per metric ton." This would translate to about 0.13 cents per liter of ethanol.^citation?
* Switchgrass is native to North America, and estimated yields vary from 500 to 1,000 gallons of ethanol per acre. ^citation?
* Test plots of switchgrass at Auburn University have produced up to 15 tons of dry biomass per acre, and five-year yields average 11.5 tons—enough to make 1,150 gallons of ethanol per acre each year¹.
* Switchgrass can be cut and baled? with conventional mowers and balers.
* Because switchgrass removes carbon dioxide from the air as it grows, it has the potential to slow the buildup of greenhouse gas in Earth's atmosphere.
* Drawbacks include the lack of breeding history compared to crops like corn, a year to establish the field, the need for nitrogen fertilizers? - although lower requirement for fertilizers than corn - and the current lack of a switchgrass infrastructure.

Researchers across the U.S. are working to solve the technical issues associated with rendering cellulosic biomass? into biofuels at scale. Until this occurs, switchgrass will remain only a potential useful source of biomass for biofuel production. Perhaps the project furthest along is the DuPont Danisco? plant in Tennessee, which will start operations using corn cobs and then change to switchgrass once its process is refined and switchgrass is available from local farmers.

External links:

NC State Clayton Research Station

References:

¹ Auburn University

² ESA Report "Biofuels: Implications for Land Use and Biodiversity"