Growers can’t expect to make money selling alfalfa for biomass right now, said Michael Russelle, USDA-ARS soil scientist based in St. Paul, MN. “But many people would argue that it is not sustainable to grow corn only for this market, and we’ve got to be willing to develop other options.”
Alfalfa should be looked at as a potential biomass crop, along with switchgrass, corn grain and stover, fast-growing trees and Miscanthus – a large semi-tropical grass, he told the National Alfalfa Symposium audience in early February.
“Right now, you grow alfalfa and you’ve got essentially one market, right?” he asked. But as a biomass crop, it can be used for feed and fuel. If the alfalfa is gasified, the resulting ash could be used as a potassium fertilizer. Alfalfa adds soil organic matter, fixes nitrogen for future crops, improves water quality, supports wildlife habitat and is aesthetically pleasing if grown near urban areas.
The use of alfalfa as a biomass crop “has potential to expand acreage, raise the profile of agriculture to 98% of our population and improve the environment. Plus it will save you some money in the long run and it’s a highly energy-efficient idea.”
Unlike some of the other potential biofuel crops, alfalfa has a strong infrastructure, Russelle said. “We’ve got private and public plant improvement organizations; private seed production and marketing companies; and variety testing, so we can have a good evaluation for an area of what variety would do the best. We’ve got the extension service and private crop consultants … machinery manufacturers and a transportation system that works very well. And we can grow alfalfa in most places in the U.S.”
Yet, since the 1950s, U.S. alfalfa acreage has declined by an average of 136,000 acres/year, in part because of changes in livestock rations to include more corn silage and soybean meal. Unlike the costs of growing corn and soybeans, however, alfalfa costs have changed little. “The prices of soybean and corn seed have gone up about 30% over the past five years.” Nitrogen fertilizer has gone up dramatically, he said. “So why aren’t we growing more alfalfa? Its seed cost is the same, you don’t have to use any nitrogen on it, you have to use some diesel, but it’s not a whole lot more than you use on the other crops.”
The answer, Russelle explained, has to do with market demand. “There just aren’t enough people wanting to buy alfalfa. What’s the price of good alfalfa now? About $150-170/ton? If there were a lot of alfalfa around, the price would be a lot lower.”
One reason to grow more alfalfa: its nitrogen-fixing capabilities, he pointed out. “It really works well with corn. That first year after alfalfa, you don’t have to apply nitrogen to corn, except maybe as starter.” The second year growers usually can apply half of what they normally would without an alfalfa rotation, although that depends on the alfalfa stand’s shape when it was plowed under.
Alfalfa also builds soil organic matter in the soil, which is important in biomass production. As more corn residue is taken off the land, soil organic matter amounts need adjusting. “Research done in the Upper Midwest suggests that if you’re growing corn after corn, maybe you can take half the stover off one year out of two and still maintain the soil organic matter. But if you’re growing corn after beans, you shouldn’t take any residue off because when you’re growing soybeans, you’re losing carbon from the soil. If we go to a biomass removal system like this, suddenly removing this ‘free’ resource, our ‘waste’, becomes a real detriment for soil quality.”
He suggests growers consider shorter alfalfa rotations to add soil carbon and nitrogen. Research has shown, he added, that two- or three-year alfalfa rotations capture more nitrates and are more productive than alfalfa grown in four-year or longer rotations. The cropping system becomes more flexible, too, he said.
Alfalfa also improves water quality because of its nitrate-capturing abilities, and it’s been used to clean up nitrate contamination of abandoned barnyards. It’s also good wildlife feed and is more aesthetically pleasing than corn when planted near urban areas.
“I told you all the good reasons to grow alfalfa. Now, could we grow alfalfa and harvest the stems and leaves separately?” he asked. Russelle answered his own question by telling how, years ago, he worked on a Minnesota alfalfa gasification project that fell through for a number of reasons. One good result, however, was the development of a method to separate leaves from stems. Newer work in Wisconsin showed that a bean stripper that takes 90% of leaves from stems could also be used, he said.
Stems could be used for biomass at about $40/ton and the leaves for meal. Russelle said estimates from years ago put leaf-meal prices at about $70/ton.
“So you put those two together and it’s still not what you get for prices now. But it’s a market. You know how fast the fuel markets are growing. It’s phenomenal.”
“We think alfalfa’s a crucial crop. It’s not going to be for everyone. Neither is Miscanthus and neither is corn. But we still have a lot of needs and these are being addressed, not only by public researchers, but also private researchers,” Russelle said. One such need: more rapid stand establishment to make shorter rotations more economical.