Bale of switchgrass, courtesy of U of Wisconsin
This bale of switchgrass probably weights around 260kg (573 lbs.) and represents approximately 22 gallons of cellulosic ethanol. Unlike fossil fuel biomass that accumulated over millions of years and gradually turned into coal, oil and natural gas, we are being asked to trust our transportation future to the year-to-year vagaries of climate, rainfall, plant diseases and pests. Photo courtesy of University of Wisconsin.

Is Switchgrass Viable?

Can America depend on a humble bunch grass for its transportation fuels future?

By Bill Moore

"That's a good question."

Have you ever noticed that when someone isn't sure how to answer a question they always seem to start with, "That's a good question"? Well, that's the situation here, folks, but before I start waltzing around the issue, let me share with you a bit of trivia Professor Vogel shared with a group of us who attended his lecture in Lincoln, Nebraska in late March to help set the stage.

The mechanization of American agriculture prior to and after the Second World War did two things: it sent vast numbers of displaced farmers into the cities to look for work and it sent equally large numbers of horses and mules to the proverbial "glue factory."

In 1920, 27 million mules and horses worked the fields of America. By 1954 there were less than 5 million. The displacement of draft animals in America not only made it possible to farm more acres with fewer people -- today less than 2 percent of the work force is employed in agriculture -- but it also freed up some 80 million acres of land that had once been required to provide feed and fodder for all those mules and horses.

All that extra farm land now became available for food production, but according to Professor Kenneth Vogel of the University of Nebraska at Lincoln, that caused another problem, too much corn and wheat drove down commodity prices to unsupportable levels for farmers. The government eventually responded with the creation of the Conservation Reserve Program that took some 35 million acres out of production, converting more marginal lands back to grassland habitat, which also had the added benefit of slowing top soil erosion, at least on CRP lands. Soil erosion elsewhere continues to occur at a rate of 11,000 pounds per acre according to a 2006 NCRS study; the natural rate of erosion is a mere 400 pounds per acre.

Now that acreage is being eyed for possible cellulosic ethanol production and the current mixture of grasses and wild flowers could be supplanted by prairie switchgrass, a deep-rooted, summer perennial that would serve as the low maintenance feedstock for regional ethanol plants. While corn stover and wheat straw will be the initial source of cellulose in some of the half-dozen experimental processing plants being built under DoE demonstration programs from Idaho to Iowa to Florida, because switchgrass requires fewer inputs -- from nitrogen fertilizers to diesel fuel to irrigation water -- and renews itself annually, it is seen as one of the preferred sources of biomass, especially across the prairie states stretching from Texas to the Dakotas.

Depending on a variety of factors from weather to soil fertility to genome type, Vogel estimates that current varieties of switchgrass yield between 6.3 and 7.4 tons of biomass per acre; and each ton should produce around 80 gallons of ethanol. Corn-based ethanol, by contrast, yields somewhere between 2.5 (Pimental) and 2.7 (USDA) gallons of ethanol per bushel. Assuming a yield of 175 bushels per dryland acre, the same field would produce 437-472 gallons of ethanol, but at significantly higher production costs. Brazilian sugarcane ethanol, for comparison, yields approximately 750 gallons per acre, and they can grow up to three crops a year.

Vogel estimates that a 50 million gallon cellulosic ethanol plant will require 17,000 tons of biomass a day produced from 125,000 acres of land. Getting the biomass to the plant would require 85 20-ton trucks, all requiring fuel, likely diesel fuel. He calculates that because of the logistical issues, the maximum radius a plant could economically support is between 25 and 50 miles. As a result, the process will require thousands of small plants instead of a few hundred large scale ones. This means that the economics of scale is limited; operating costs will be higher because the increased capital investment and lower operating efficiency. It does, however, promise more jobs for rural communities.

Of course, switchgrass is only one of a number of biomass sources being investigated. One of the more obvious is corn stover, the residue of stalks, cobs and leaves left in the field after harvest of the corn kernels. Here the logistics are just as daunting as that for switchgrass.

In an article in the Omaha World-Hearld, reporter Bill Hord, talked to various midwest experts about the economics of using corn residue for cellulosic ethanol production. He reported that it would take 67,000 semitraller loads of chopped and bailed stover to supply 1 million tons of feedstock for a 80,000 gallon refinery. That's 187 truck loads a day or one every eight minutes; and what fuels those trucks?

The World-Herald article cites a three-year study out of Chase County, Nebraska that "indicates that an 80-million-gallon ethanol plant would require corn stover from 500,000 acres of corn within a 50-mile radius of the plant and 500 acres to store it after harvest."

How to keep the material dry enough to prevent rot and wet enough to prevent spontaneous combustion is still being investigated.

Hord also notes that collecting the stover would come at the busiest time of the harvest season in terms of manpower and equipment and that given corn prices are likely to be much higher than the price for stover -- or switchgrass -- many farmers are questioning the economic rationale for bothering, especially since leaving the residue in field helps slow erosion and preserves the friability of the soil.

Author Alice Friedermann points out in her critical review of the impact of energy crop farming on the soil that "energy crops are subject to Liebig's law of the minimum too. Switchgrass may grow on marginal land, but it hasn't escaped the need for minerals and water. Studies have shown the more rainfall, the more switchgrass you get, and if you remove switchgrass, you're going to need to fertilize the land to replace the lost biomass, or you'll get continually lower yields of switchgrass every time you harvest the crop." Her source for this conclusion? Professor Kenneth Vogel.

So ultimately, even switchgrass will have to have nutrients added back to the soil. It would seem there is no free lunch even with this promising cultivar. In his presentation in Lincoln earlier this Spring, Vogel concluded that not only will farmers need to be educated on why and how to cultivate and manage switchgrass, but that new, improved varieties will be needed and even then, the economics will be challenging.

He pointed out that it takes 1000-1200 lbs of biomass like switchgrass to produce a 50 gallon drum of ethanol and we American's consume 384.7 million gallons of gasoline a day! Even vocal proponents of cellulosic ethanol like Jim Woolsey, the one-time head of the CIA, admit that, at best, it could only supply 30% of America's current gasoline consumption, which is why he has become such a strong proponent of plug-in hybrids.

Biofuels offer a promising pathway, but not based on our current consumption practices. We're going to have to do much better with a lot less. Maybe we need to start thinking about feeding mules that switchgrass instead of our cars.

Times Article Viewed: 8021
Published: 06-May-2007


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