Two years of alfalfa rotated with corn could provide cellulosic biomass, high-protein feed for livestock, higher corn yields and additional soil nitrogen — among other benefits, says Hans Jung, USDA-ARS researcher.
He spoke at a late-June workshop called “Alfalfa-Corn Rotations for Sustainable Cellulosic Biofuels Production.” It was hosted by the National Alfalfa & Forage Alliance and National Corn Growers Association and sponsored by alfalfa seed companies and seed producer organizations.
“Why are we interested in alfalfa-corn rotations?” Jung asked the university experts, growers and seed and biotech company representatives who attended. “National bioenergy goals require that we produce vast amounts of biomass. Here in the Midwest, we are standing on some of the best farmland in the country. So it's our opinion that the Corn Belt can't be excluded from this need to produce biomass.”
That doesn't have to mean a reduction in the food and feed supply, he stressed. “We think one of the most unique things about alfalfa-corn rotations is that they maintain food and feed production, while providing us with a sustainable cellulosic biomass supply. And all that can be done without plowing additional acres.”
Corn grain yields will increase by 5-15% following two years of alfalfa as compared to corn following soybeans, according to studies Jung cited. Alfalfa also produces its own nitrogen and leaves enough residual N to supply 75% of what's needed in the following two years of corn.
While alternative cellulosic biomass crops such as switchgrass have yet to build infrastructure, alfalfa already has one, he added.
“The fact that we are an established crop is one of our biggest advantages. We harvested 21 million alfalfa acres worth $8 billion in terms of product (in 2009). We have varieties, seed companies, equipment and, most of all, we have experience.”
Environmental advantages include fewer greenhouse gas emissions plus reduced nutrient runoff — because less nitrogen fertilizer is being made and used. Reduced soil erosion is another; the perennial provides ground cover and requires less tillage.
“Finally, alfalfa is a very deep-rooted crop that puts a lot of biomass below the plow layer, so we should see an increase in carbon sequestration.”
Considering alfalfa as an energy source isn't new, Jung said. In 1993, work was done to develop a facility utilizing alfalfa stems to produce electricity and leaf-meal protein. But for funding and other reasons, the Minnesota Valley Alfalfa Producers' project collapsed.
“We learned some lessons from that project; corn and soybean farmers were very willing to entertain the notion of adding alfalfa to their crop rotations. In some cases, it was because they had experience … in using alfalfa. They saw the advantages of an N-fixing perennial for a lot of reasons, including breaking up pest cycles.”
The project also showed that alfalfa could be separated into two products and that alfalfa-leaf meal could replace soybean meal as a protein feed for dairy and beef cattle.
Jung and others envision two years of alfalfa — seeding year and one full production year — harvested as two products at least two and up to four times each of those years. The alfalfa is then plowed down and followed by two years of corn with reduced fertilization. Corn grain is harvested for food and feed and stover is used as biomass.
Making some assumptions, Jung compared three cropping systems' viability for ethanol and protein yield. A corn-on-corn rotation can produce the most ethanol — 618 gallons/acre, and the least protein, at 0.40 ton/acre. A corn-soybean rotation can provide 373 gallons/acre of ethanol (including biodiesel on an ethanol energy equivalent basis) and 0.46 ton/acre of protein and an alfalfa-corn rotation, slightly more ethanol, 399 gallons/acre, and slightly less protein — 0.44 ton/acre.
“How do you choose between these systems? If you just want total ethanol production, continuous corn would seem to be your choice. If you're worried about maintaining a protein supply, then you have a choice between corn-alfalfa and corn-soybeans without a real good reason to choose one or another. So a lot of other things, such as environmental impacts and net energy, are going to have to play into that decision.”
An alfalfa-corn rotation offers growers and bioenergy companies a wider window for biomass harvests. Corn stover is fall-harvested over a two-month period and would require storage over 10 months. Alfalfa, harvested during the summer, would reduce storage capacity needs by 30%, Jung said.
But there are challenges. The process and equipment that separate alfalfa leaves from stems need research. Kevin Shinners, the University of Wisconsin ag engineer who discussed several fractionation possibilities, has developed a harvest-fractionation machine that strips alfalfa leaves from stems at harvest. (Read “Alfalfa: Queen Of Biomass, Too?” in our March 2009 issue or online at bit.ly/9hqq8V.)
“Our prototype machine needs considerable additional development work before it would be considered for the marketplace,” Shinners said at the workshop. He also suggested that now may be the time to refocus development work on fast-drying maceration technology.
A tall, thick-stemmed, non-lodging alfalfa has been developed, as well as a biomass management system that, combined, can produce a total biomass yield that is 40% higher than a traditional hay system's yield, according to University of Minnesota and USDA-ARS researchers. But growers and biofuel companies need more data and a game plan, workshop speakers agreed.
One speaker didn't like pairing corn with alfalfa. With corn yields increasing, there may be a better crop for alfalfa to join forces with, said Jeffrey Steiner, the USDA-ARS national program leader for biomass production systems and an agronomist.
“We have to think about what grows where and what comes from where. And we have to set our minds as to what is already being used from those lands,” he said.
Research funding is needed and agronomic, environmental, logistical, conversion, economic and policy issues all need further study, workshop hosts concluded. A committee to develop an action plan was formed.