USDA study: Grass more efficient for ethanol than corn

William Atkins
Wednesday, 09 January 2008 20:05

Science - Energy

The United States Department of Agriculture (USDA) has shown that switchgrass can be grown without replacing existing crop lands, can produce five times more energy than what it takes to grow it, and can be environmentally friendly.               

A USDA study co-conducted by plant scientist Ken Vogel (a geneticist with the USDA’s Agricultural Research Service based out of the University of Nebraska, Lincoln) studied switchgrass—a native North American perennial herbaceous plant with the scientific name Panicum virgatum.

Switchgrass, also commonly called tall prairie grass, Wobsqua grass, lowland switchgrass, and other such names, is a warm season grass that is commonly found in the central North American tall-grass prairie.

The USDA team studied farmers in Nebraska, North Dakota, and South Dakota as they farmed switchgrass as a possible cellulosic bioenergy crop.

The farmers kept records on the amount and kinds of seeds, fertilizer, and fuel used to plant and harvest their crops of switchgrass. They kept records of the amount of rainfall on their crops for five years on fields of switchgrass that ranged in size from 7 to 23 acres (3 to 9 hectares).

Vogel stated that once the fields matured the farmers harvested between 5.7 and 12.2 U.S. short tons (5.2 and 11.1 metric tons) of grass bales per hectare (with one hectare equaling about 2.5 acres). The range of harvest depended primarily on the amount of rainfall.

According to the latest studies, the use of switchgrass for the production of ethanol would deliver 540 percent of the energy used to produce it. Vogal says, in comparison, using corn for the manufacture of ethanol produces only about 25 percent more energy.

In other words, for the amount of energy input to produce ethanol (in the form of fertilizers and fuel), corn only produces 25% more energy while switchgrass produces 540%, over five times the amount.

One of the reasons why switchgrass produces so much more ethanol is that the entire plant is used, whereas only the kernel is used in corn-based production of ethanol.

Vogel contends, however, that the five times amount is only an estimate right now because there are no factories (what are called biorefineries) in existence that produce switchgrass ethanol. However, Vogel states, “We’re pretty confident the ethanol yield [with switchgrass] is pretty close.” [Scientific American: "Grass Makes Better Ethanol than Corn"]

According to the U.S. Department of Energy, six cellulosic biorefineries are being partially funded by the government, with the first one (Range Fuels Biorefinery) being built in Soperton, Georgia. [DOE: http://www.doe.gov/news/4828.htm]

A cellulosic biorefinery will be able to take any wood product, such as sawdust, wood chips, and switchgrass, and make it into biofuel. (A list of biorefinery locations in the United States is found at: http://www.ethanolrfa.org/industry/locations/.)