PESOTUM, Ill. — Eric Rund said recent rains will help the 35 acres of giant miscanthus (Miscanthus x giganteus) growing on his Pesotum farm. Still, he expects yields will still suffer from the drought.

“It’s still too early to tell how much yields will go down,” said Rund, who chopped 60 tons of miscanthus last year. “But I can say that miscanthus yields are not going to suffer like the corn.”

The drought tolerance of crops with bioenergy potential, like giant miscanthus and switchgrass, is well established. “These are both C4 grasses, warm-season grasses that have a good ability to tolerate heat and drought,” said Tom Voigt, University of Illinois extension specialist.

But exact yield losses from drought are difficult to predict.

“Yields can be affected by many factors, including the age of the stand, soil types and fertilization,” said Voigt. “There’s no way to get around some yield reduction from a drought.”

Both men are eager to observe yields from the 140 acres of miscanthus weathering this year’s Illinois drought. “We think that southern Illinois is a great spot for energy crops because of the rolling terrain,” said Voigt.

He said giant miscanthus can yield up to three times the amount of dry matter per acre as switchgrass. Yield impacts of drought on switchgrass are better documented than giant miscanthus because switchgrass has been long evaluated as a forage.

“In a drought year, switchgrass shines,” said Fred Allen, coordinator of Agronomic Variety Testing at the University of Tennessee. “During our most severe heat and drought in late June of this year, switchgrass was green and growing, whereas fescue was as brown as a biscuit.”

UT researchers recorded yields for established switchgrass during a four-year period, including a record-breaking drought year in 2007. Pat Keyser, director of the Center for Native Grasslands Management, said there was a 35 percent drop in yield compared to the four-year average in 2007.

But Keyser said switchgrass yields could vary widely between similar drought years. “As agricultural crops go, switchgrass is strikingly drought-tolerant,” he added.

Ken Goddard, UT extension specialist in switchgrass, agreed. He is involved with 5,100 acres of switchgrass planted on 61 farms in East Tennessee. “My guesstimate is an average 20 percent yield loss for switchgrass in dry years,” he said.

The secret to switchgrass drought tolerance is in its extensive root system, said Goddard. “We’ve repaired sinkholes in switchgrass fields and seen the roots as deep as the plant is tall.” Switchgrass reaches a height of eight feet in Tennessee.

The deep roots also give switchgrass an advantage when grazed or hayed in the spring before being stockpiled for biomass harvest. Keyser said based on preliminary analysis, early-season grazing or haying reduces biomass yields by a 1:1 ratio.

“So if you graze two tons, you see a two-ton reduction in biomass yield,” he said.

The grazing can have positive wildlife habitat benefits, he explained.

“Our research is indicating that grazing to a height of 12 inches, and then stockpiling for biomass, actually improves switchgrass habitat for grassland birds.”

But new switchgrass plantings are susceptible. “Here in eastern Tennessee, we haven’t had much drought to affect this (5,100 acres of) switchgrass,” said Hem Bhandari, a UT plant breeder working on improving it for biomass.

Drought can especially devastate new switchgrass plantings.

“Dry soils immediately following germination can totally destroy these young plants,” said Goddard.

The extensive Tennessee planting tested switchgrass on a variety of soil types and growing conditions, in an area extending from Knoxville to Chattanooga, for the UT Biofuels Initiative, a program started in 2007. Farmers contracted with UT to grow switchgrass for use in a pilot plant in Vonore. The plant is expected to go online with switchgrass next year, researchers said.

In Illinois, Rund, who farms 750 acres of row crops, said his giant miscanthus will grow more than nine feet tall. With stems similar to bamboo, it will be chopped with a self-propelled forage harvester this winter. Much of Rund’s crop is now used for animal bedding.

Rund, who became interested in miscanthus after seeing that the crop was used to heat homes in Germany and Austria, is cautiously optimistic about its future. He is shipping a semi load of giant miscanthus chips to be used in the development of a U.S.-built home heating unit.

“Right now, I could see the best use for miscanthus as a replacement for LP gas on rural farmsteads,” he said. He plans to install a miscanthus heating unit in his own home, for use in future winters long removed from this summer’s heat.