Despite reductions in yield after five years of growth, miscanthus consistently produced double the yields of switchgrass, according to a 10-year study of the two perennial crops grown to be used as bioenergy feedstocks.
The average annual yield of miscanthus during that period was 10.5 tons/acre vs. 4.5 tons/acre for switchgrass grown in side-by-side trials in Illinois, say University of Illinois researchers.
In the study, yield differences that were the result of annual weather changes – primarily heat and precipitation, both of which increased growth – were taken into account.
Miscanthus does almost as well in poor soils as in fertile cropland, adds Stephen Long, the plant biologist who led the study.
“It takes a little bit longer to establish miscanthus in poorer soils, but once it’s established the yields seem to be almost as good as in the very best soils.” Yield differences between richer and poorer soils were less than 10%.
Like what you're reading? Subscribe to eHay Weekly and get the latest news right to your inbox.
Several U.S. growers pelletize miscanthus for use as a renewable, carbon-neutral energy source. Pellets are burned to produce electricity or heat, and there’s a growing market for pelletized miscanthus in the U.S. and in Europe, Long says.
“However, the expected long-term and larger market for miscanthus is in digesting the celluloses in the biomass to sugars for fermentation to ethanol and other liquid fuels. This would complement corn ethanol, since it would allow the use of land unsuited or marginal to corn and other row crops.”
Using miscanthus to meet the current U.S. Renewable Fuel Standard mandate of 16 million gallons of cellulosic ethanol production by 2022 would require 17 million acres vs. 39 million acres of switchgrass, Long says.
“That 39 million acres sounds like a lot and is a lot, but keep in mind that the 48 contiguous states are almost 2,000 million acres,” he says.
“We use only about a fifth of that in our row-crop agriculture – cotton, corn, soybean, wheat, etc. And we actually have at least 550 million acres that have been abandoned from agriculture in the last 150 years. This is not land that has been lost to urban sprawl.”
Long believes miscanthus could be grown on former ag lands left unused after the Dust Bowl to prevent soil erosion. Or it could be grown on Conservation Reserve Program lands.
“We have 40 million acres in the Conservation Reserve Program. “A crop like miscanthus would be suitable for that land because it doesn’t have the same erosion problems of an annual crop. You’re not plowing the land every year, and you have a dense perennial root system that binds the soil.”
The crop accumulated more roots over a five-year period than did plants on fallow land or even native prairie. Miscanthus can be grown with little or no added fertilizer, he adds.
In another study, Long and colleagues added nitrogen to miscanthus and switchgrass, significantly improving yields over time (by 25% and 32%, respectively). This eliminated age-related declines in yield seen in switchgrass and about 40% of the loss found in miscanthus. But the increases are probably not large enough to justify the added cost of fertilizer, the team reports.
“The bottom line is, if we simply plant miscanthus and leave it, we don’t see the same yield at year eight and year 10 that we saw in years three and five,” Long says. “But we’re still seeing a very high yield.”
You might also like: