When forage agronomist Steve Fransen began looking at growing switchgrass for cellulosic ethanol production, he quickly concluded that much of the research from the central and eastern U.S. wasn't going to apply to Washington State.
“I said to myself, what they're doing back East is never going to work here,” recalls Fransen, of Washington State University (WSU). “Our growing conditions are entirely different.”
That doesn't mean growing switchgrass for biofuel won't flourish in his state, he adds. On the contrary, he's confident that Washington will be a national leader in the number of dry tons produced per acre.
“It just won't be dryland production,” he says. “What we're looking at is switchgrass under pivot.”
What Fransen envisions is already happening on a smaller scale in central Washington's Columbia Basin.
“Rainier Seeds, Inc. has been growing irrigated switchgrass for seed for over 20 years,” he says, adding that the grass has always been in demand for conservation projects. “I first saw circles of switchgrass in the Columbia Basin in 2001, when agronomists from Rainier toured me around switchgrass seed fields they had been growing.”
Some of the fundamentals of growing switchgrass for seed could be applied to his work. Yet Fransen discovered in his own research trials at WSU's Prosser Center that growing the grass for biofuel would require serious tweaking.
“First, for seed production there is only one cutting,” he says. “We soon learned that when you're growing for biofuel production in this region, it makes sense to take two cuttings — one early to mid-July when the grass is fully headed and a second in September or October.”
He notes that Washington's two-cutting scenario may be a major departure from areas of the country where one cutting a year is usually the norm.
“The advantage we gain from cutting twice is increased yield. Our research has shown that, under normal conditions, we constantly average over 10 tons of dry matter per acre.”
WSU researchers have found that when they take two cuttings, it's absolutely essential to leave at least 6” of stubble after each harvest.
“If you cheat and leave less, you'll get little if any regrowth after the first cutting and stand losses will greatly increase due to plant death over the winter,” says Fransen. “The plants need those carbohydrate reserves after the first and second cuttings.”
Because of the amount of biomass being removed, he points out that WSU's system requires more nitrogen. His research group has been applying up to 100 lbs/acre of N in spring and another 100 lbs after the first cutting. Phosphorus and potassium applications are based on soil tests and can run around 100 lbs of P and up to 200 lbs of K.
“We don't fertilize the first year because weeds are enough of a problem already.”
Like in the rest of the country, the biggest issue facing stand establishment is weed control. To deal with the problem, Fransen and his research team treat their new sites with pre-emergent atrazine herbicide.
“This helps suppress weeds for one to two months, allowing the switchgrass to reach a height of around 4”,” he says. At that point, any weeds taller than the grass are topped mechanically. “This prevents the weeds from going to seed and opens up the canopy to the switchgrass.”
The following March, while the switchgrass is still dormant, Fransen's team checks for early emerging winter weeds. If they find weeds, they apply glyphosate before switchgrass breaks dormancy.
“This check should be repeated every year followed by a treatment when necessary,” says Fransen. “That way you're always ahead of any potential weed infestation.”