With the prices growers can get for alfalfa, you'd think it wouldn't be considered as a potential biomass crop. Yet university and USDA researchers see the Queen of Forages as having a unique niche in the cellulosic market.
It's a crop that growers can harvest as two distinct products — right from the field.
“The idea with alfalfa for biomass is that stems would be used for feedstock and leaves would be a value-added product, either as animal feed or for extraction for proteins or other components,” says Michael Russelle, a USDA-ARS soil scientist. “So you're not just growing something that is used for ethanol or electricity production; it has a couple of streams of income.”
Minnesota and Wisconsin researchers are currently working on a biomass alfalfa, an alfalfa production system and a harvesting machine to help alfalfa adapt to the biomass market.
JoAnn Lamb, a USDA-ARS geneticist, is developing a thick-stemmed, winterhardy, disease-tolerant alfalfa that won't lodge when cutting intervals are longer than normal, says Russelle.
Lamb and Craig Sheaffer, University of Minnesota forage agronomist, have developed a production system in which this biomass alfalfa is seeded at a lower rate to allow for increased stem production. It's then harvested only two or three times a year vs. four or five, thereby reducing energy inputs, Russelle adds.
“Hans Jung, our ARS colleague, figures we can double the ethanol production that you would get from the normal forage harvest system — and still have a value-added stream using leaves as an animal protein supplement, for example,” he reports.
The third piece of the alfalfa-for-biomass puzzle is a leaf-stripping harvester designed by Kevin Shinners, University of Wisconsin ag engineer. He says it will work with other forage or biomass crops, too.
“The objective of the project was to create a valuable livestock feed while simultaneously creating a high-fiber feedstock that would be shipped off and be used for energy production,” Shinners says.
The machine can strip leaves off plants such as alfalfa, switchgrass or other grasses and legumes while cutting and laying stems in windrows. In a second pass, growers can chop or bale stems for delivery to a nearby biorefinery or electrical plant.
“If you're trying to make ethanol out of alfalfa, you don't need the protein — you need the fiber. So where is most of the protein in a plant? It's in the leaves. So let's keep those leaves on the farm and use the stems for energy production,” Shinners says.
He mounted a stripping reel from a snap bean harvester, in addition to other parts from other equipment, onto a forage harvester. “We had the first generation of this machine in the field during 2008, and we found plenty of new design challenges,” he says.
One such challenge: how to deal with leaves that are probably in the 70- to 80%-moisture range. “We have to figure out a way to safely store the leaves to use for animal feed.”
Grass leaves are easier to ensile because they're at the right moisture content, he says. “But grass leaves don't have the protein content that alfalfa leaves do. You're not producing as high a protein feed with grasses as you would like. They're going to have less value.”
Extension forage specialist Dan Undersander, also with the University of Wisconsin, says biomass may be profitable for growers if they produce two products from a crop like alfalfa.
“If you're taking $180/ton dairy feed off the top, then you can afford to sell the bottom half for $50/ton. Then you start to get economies to work.”
Alfalfa has other advantages, adds Pete Vadas, USDA-ARS dairy systems scientist. “It fixes its own nitrogen. If you follow with corn, the alfalfa supplies some nitrogen to the corn crop.”
Alfalfa is also a well-established crop growers know how to grow, with a large industry to support it, Vadas adds.