A native grass that once fed buffalo herds on the prairie may someday feed power plants in the Wisconsin countryside. Switchgrass farming could produce a new cash crop for Wisconsin farmers, while improving wildlife habitat, reducing air and water pollution, and lessening soil erosion, say University of Wisconsin-Madison researchers.
A “biomass” crop that”s burned to generate energy must be practical and profitable for the farmer, and feasible for the power company. Switchgrass shows great potential many farmers already have the machinery to handle it, it burns well, and it”s environmentally friendly. Economically, biomass fuels can”t compete with coal right now, but government incentives and public support for renewable fuels could change that.
Switchgrass is a native prairie species that originally grew from the Gulf of Mexico to Canada. A bunchgrass, it grows in clumps and can reach more than 5 feet in height. Switchgrass doesn”t form a solid mat, but leaves litter-covered areas between clumps that can shelter wildlife; the litter also reduces erosion, explains Laura Paine, an agronomy research specialist at UW-Madison”s College of Agricultural and Life Sciences. Switchgrass plants can live more than 20 years, and will tolerate yearly cutting. Switchgrass is hardy and drought-tolerant, and with minimal fertilization can produce 2 to 6 tons of dry biomass per year. Some switchgrass varieties are now available for biomass production, and even better varieties are in the pipeline, according to Dan Undersander, CALS extension agronomist.
Alfalfa fields are usually cut three times a year, when the crop is most nutritious. Biomass producers aim for maximum tonnage per cut; nutritional quality doesn”t matter, Undersander explains. Taking a three-cut field and reducing it to one or two cuts saves labor, time, and machinery wear and tear. Many farmers already have seeding and harvesting equipment that can handle switchgrass, he notes.
Switchgrass and other perennial ground covers, once established, reduce both wind- and water-caused soil erosion, while adding organic matter to the soil. Switchgrass requires less fertilizer and pesticide than annual row crops, and the year-round ground cover reduces potential for runoff.
CALS researchers monitored vegetation and bird activity in switchgrass fields during May, June and early July. Using standard haying equipment, they mowed and baled the switchgrass in mid-August. This was late enough to spare ground-nesting birds, but early enough to allow some regrowth, which provides early season cover for birds returning to nest in the spring, according to Paine. The large round bales, weighing about 750 pounds each, were harvested from Conservation Reserve Program lands in Iowa and LaFayette County. Each bale contained the energy equivalent of 490 pounds of coal, or 41 gallons of gasoline or fuel oil.
A series of co-firing tests in Madison Gas and Electric Co.”s 50-megawatt boiler burned a mix of switchgrass and coal, containing up to 10 percent switchgrass. The switchgrass was chopped into bits and blown into the boiler with the coal, using the system originally developed to burn Madison”s waste paper.
The heat rate was 3 percent higher co-firing with switchgrass than burning coal only. Sulfur dioxide emissions were unchanged; visible smoke was cut in half and nitrogen oxides were reduced 20 percent compared with burning coal only, according to a report by Ken Ragland and Danny Aerts, UW-Madison Department of Mechanical Engineering. Co-firing didn”t affect the boiler, although some unburned switchgrass showed up in the bottom ash. About 180 tons of switchgrass were burned in the tests.
Burning fossil fuels releases fossil carbon, adding to the atmosphere”s carbon dioxide load. Biomass crops recycle carbon by absorbing atmospheric carbon dioxide while growing and releasing that carbon when burned. Some evidence shows that switchgrass and other native prairie species actually sequester more carbon in their root systems than they release when harvested and burned, Paine reports.
“Biomass crops can be a plus or minus for wildlife, depending on where and how you plant them,” says CALS wildlife ecologist Stan Temple. “If lands for biofuels come at the expense of natural habitats already occupied by wildlife, then there will be problems.” Raising energy crops on lands currently farmed conventionally can be a plus a switchgrass plantation, even if a monoculture, will be more useful to wildlife than a cornfield, Temple says.
Several types of agricultural lands would benefit from switchgrass production, according to Paine: highly erodible lands, wetlands that have been drained and farmed, and marginal agricultural land in certain areas. As contracts expire, Conservation Reserve Program acreage could be converted to switchgrass biomass production. This would let farmers bring CRP lands into production without breaking the sod or sacrificing the other environmental benefits of CRP, Paine points out.
Data from 1997 should reveal the effects that switchgrass harvest may have on the vegetation structure and bird communities in CRP fields, according to Paine and Undersander. They hypothesize that cutting may actually enhance the habitat for some declining species, such as grasshopper sparrows and dickcissels, which tend to avoid tall, dense vegetation.
Harvest timing is crucial for sparrows, bobolinks, dickcissels and other grassland birds, Temple points out. Warm-season grasses, including switchgrass, are cut in late summer or fall, after ground-nesting birds are finished nesting. Cool-season grasses are cut at the worst possible time for ground-nesters in late spring and early summer when the birds are on their nests.
The economics of switchgrass will depend largely on government actions. If Wisconsin mandates power production from renewable sources, as Minnesota and other states have done, switchgrass would be a very good choice, Undersander says. Coal now costs about $20 per ton; to grow, harvest and deliver switchgrass to a utility costs $40 to $50 per ton. However, states are beginning to put incentives on renewable fuels and disincentives on fossil fuels. These tax breaks could bring the costs of switchgrass and coal closer together, Paine notes. Surveys have also shown that many people are willing to pay extra for “green” electricity generated from renewable resources.
This research is part of an effort by the Agricultural Ecosystems Research Group, a group of scientists from the UW-Madison, the Wisconsin Department of Natural Resources, and Madison Gas and Electric Co. The researchers expect to report final results by the end of 1997.