Be realistic when projecting yields of biofuel crops
The high yield potential of energy crops like switchgrass and miscanthus, demonstrated in university and company research trials, generates plenty of buzz in the countryside. But farmers mulling over prospects for planting these crops need to scrutinize research results carefully before plunging into production, says Tom Keene, University of Kentucky hay marketing specialist.
“There certainly is fantastic potential,” says Keene. “However, farmers looking at the various trial results need to remember that most of these studies are done under very closely regulated conditions. They're done on the best of soils, they get great weed management and very exact fertility management. Everything is done absolutely perfectly.”
With switchgrass, for example, Keene notes that researchers have reported yields of 4-6 tons and as high as 18-19 tons of dry matter/acre.
“The numbers are certainly factual,” says Keene. “But when we get on farms in different areas of Kentucky, we're not going to be able to match those kinds of yields with our soils, our slopes, our rainfall and so forth.”
Some of the higher reported yield numbers are from plots that have been in production for three or more years, Keene says. In general, switchgrass yields lag in the first year or two while the stand is getting established.
“But in Kentucky, even once we get mature stands, we're not going to see those kinds of yields. We'll be able to get a good crop, but it won't be anywhere close to some of the higher yields projected.”
For miscanthus, Keene says he's seen reports of 14-17 tons/acre all the way up to 24-25 tons.
“Again, that research has been done on some very good soils, under some optimum growing conditions. But the jury is still out. My thinking is that 7-10 tons/acre might be more realistic. There might be some isolated instances on better river-bottom ground where we could get a little bit more than that. But it wouldn't be anywhere close to some of those higher numbers.”
In evaluating research results, Mike Casler, a forage geneticist at the U.S. Dairy Forage Research Center in Madison, WI, advises producers to ask detailed questions about how the research was conducted, starting with where the data was collected.
“You want to look at varieties that come from the same region you're in,” he says. “Miscanthus, for example, hasn't been tested extensively in many parts of the U.S. If you're in northern Wisconsin and the research was done in southern Illinois, the trial results may not tell you all that much.”
Often, results from research at one location within a state will hold up for the entire state.
“In Iowa, for example, if a switchgrass variety is adapted to one location in the state, it will generally be adapted to the entire state. On the other hand, that may not be true in a state like North Dakota, where you have major variations in climate and environmental conditions in the eastern or western areas of the state.”
You'll also want to know more about the intensity of the management in the research trials. Casler recommends asking about how much fertilization was needed and what other inputs went into growing the crop. “That will give you a better overall picture of the economics that might be involved,” he says.
Knowing about the soil type of the research plots may or may not be as important as some other factors.
“A lot of the test plots at experiment stations are on good land, but one of the things that has generated interest in perennial grasses is that they can often be grown successfully on marginal soils as long as there's adequate water available,” says Casler. “It can be tough to evaluate. We'll learn a lot more as we get more results from on-farm studies.”
Producers should scrutinize research results carefully when trying to estimate yield potential, encourages Tony Brannon, who has grown switchgrass on 15 acres of his family's 650-acre farm near Puryear, TN, for the past five years.
“The research is what it is,” says Brannon, who is also dean of the School of Agriculture at Murray State University near Murray, KY. “Typically, what you'll find is that yields on small plots (in research trials) will be higher just from the standpoint of things like micromanagement and field variations.”
The Brannons planted an Alamo variety as part of a University of Tennessee pilot project aimed at supplying biomass feedstock for a power plant. Discounting the first year, when yields are typically low due to establishment challenges, Brannon reports that yields averaged 6.5 tons/acre in years two through four. In two of those years, yields were likely held in check by severe drought conditions. Soybean yields during those two years, by comparison, were just 8 and 15 bu/acre.
In 2009, with a return to more normal weather, Brannon was expecting yields to improve to 7-8 tons/acre.
“I've seen figures of 6 or 7 tons up to 11 tons/acre for switchgrass. My thinking is that if you take out the extreme weather, our yields would have been right in the middle of that.”
Brannon's bottom line on evaluating research yield results: “It's kind of like when you go to buy a new car, and you've got a sticker on the window that tells you how many miles per gallon the car might get. Then you read down to the bottom, and it tells you that the actual mileage may vary according to use. It works the same way with these (energy) crops. Depending on soil, climatic, environmental, fertilization and any number of other factors, the results are likely to vary.”