Putting Alfalfa to Work in the Environment
Written by Daniel Ungier, MISA intern, December 2002
Can alfalfa save the world? Maybe not quite, but a growing number of people believe it can be used for far more than livestock feed. Alfalfa is the most widely grown legume in the U.S, with estimated sales of $6 billion a year, and it is now gaining new recognition for its environmental qualities as well.
"We want to find new ways to use alfalfa because it's such an amazing plant for the ecosystem and for farm systems," says JoAnn Lamb, who is leading a team of researchers breeding alfalfa for new uses. "We want to expand it beyond its role for livestock [and] put more alfalfa on the landscape." Already, alfalfa is credited with reducing the need for nitrogen fertilizer, improving soil organic matter, and preventing soil erosion. When used in rotation with other crops, it increases species diversity and interrupts pathogen and pest cycles that affect crop yields. Lamb hopes that alfalfa's many benefits can be harnessed so that it can provide a positive long-term effect on the farm environment.
Most importantly, by exploring new uses of alfalfa, Lamb hopes to increase the demand for the product. "The low economic return of alfalfa hay makes rotations with alfalfa unattractive to many growers," explains Lamb. "New uses of alfalfa will help maintain a quality environment and sustain rural agricultural economies."
Alfalfa for energy
One innovative possibility being researched by Lamb's team is using alfalfa for producing biofuel. "Developing alternative energy systems such as biofuels from crops will create jobs and economic opportunites," says Lamb. In such a system, alfalfa would be left to mature in the field, and the stems would be processed to generate biofuel, while the leaves would continue to serve their role as livestock feed.
This double harvest, argues Lamb, makes the idea of using alfalfa for energy more realistic, as well as more economically feasible for farmers. "The key to success for an alfalfa biofuel production system would be to develop a system that would maximize both leaf and stem yield," she says. Since historically, alfalfa breeders have concentrated on minimizing stem production, that's where her work as a plant breeder has begun.
"We need to put biomass into the stems," says Lamb. "We've always taken it at immature stages. After forty years of being bred to be thin, when they mature, they fall over and the stem and leaves rot. For the first time, stems are valuable to us."
Lamb has found a European variety of alfalfa with large stems; but not surprisingly, it isn't adapted for the Midwest's climate or its local diseases. By crossbreeding the European variety with a standard Midwestern winter-hardy variety, Lamb hopes to create an alfalfa variety well-suited for the production of biofuel.
The process, Lamb acknowledges, could be a long one. After all, there is very little information about what sort of plant traits would be most desirable for biofuel. Consequently, Lamb's project is researching what would at first glance seem to be an entirely unrelated subject: the digestibility of alfalfa stems by livestock. But as it turns out, the process of digesting stems is quite similar to fermenting them for biofuel. "Rumen digestibility will give us a clue as to which alfalfa ferments well [for fuel]," Lamb explains.
A major challenge in this area is that there is no information about whether an alfalfa plant's digestibility, determined primarily by fiber content, is a genetically inherited trait, or a factor that is determined by the environment. Her project has focused on determining whether digestibility is genetic or not, information which will prove crucial before she can begin breeding the plant for increased digestibility.
Alfalfa for pollution control
A second major property of alfalfa being explored by Lamb's project has been using alfalfa to eliminate toxins from contaminated water and land. In particular, they are exploring alfalfa's ability to prevent the leaching of nitrates from the soil to the groundwater supply. Nitrate pollution often results from heavy fertilizers. Nitrates have contributed to the pollution of drinking water sources, natural habitats, and the Gulf of Mexico, which is the end destination for agricultural run-off along the entire length of the Mississippi River.
Lamb's team believes that planting alfalfa can actually help improve water quality in contaminated areas. Like all other plants, alfalfa absorbs nitrate from the soil for growth; but because of its exceptionally long taproot, alfalfa can reach deep groundwater not accessible by annual crops, at levels where concentrated amounts of nitrate often accumulate. In addition, because alfalfa is a perennial crop, it can uptake nitrate runoff as early as April; two months before annual crops even begin to grow and get their roots established.
The process, termed phytoremediation (literally, plant remedy), will require an alfalfa with "tolerance to environmental conditions, long root growth, and extensive root biomass," Lamb says. "To optimize alfalfa's potential to capture and remove nitrate at deep soil depths, alfalfa cultivars with rapid root elongation rates and extensive root densities are needed."
Lamb is planting alfalfa in soils where a bleaching agent has been placed at a predetermined depth underground. By observing when the leaves of each alfalfa plant begin to bleach, she can discover which plants have the fastest growing roots. She is also experimenting with developing root systems that include not only taproots, but smaller branching roots and fibrous roots, which increase the overall area of soil in direct contact with the plant. "When it comes to phytoremediation, you want a root system that will spread out and reach all the contaminants in the soil," Lamb says.
In a similar project, Lamb's team is looking at improving alfalfa's ability to take up metals such as aluminum from the soil. All plants are endowed with the natural ability to do so to some degree; Lamb would like alfalfa to take up enough metal to positively affect soil quality. "We want the plant to be able to uptake those metals and put them into the leaves where we can harvest them out," she says. "It all depends on getting the plant to where it's adapted to the chemistry of toxic soils."
And finally, Lamb would like to see alfalfa tolerant to manure application by farmers. Spreading manure on land is an age-old practice because manure serves as a natural fertilizer. However, manure's high levels of ammonium and salt often kill the plants directly underneath the application. "In the spring and fall, it's not a problem," says Lamb, since there aren't any crops growing at those times. "But in the growing season, the grower doesn't have a place to put the manure." If alfalfa crops can be bred to be tolerant to the ammonium and salt in manure, she thinks, then they can become an environmentally safe destination for manure in the summer season.
Thinking long-term
The goals for alfalfa's uses may be ambitious, but Lamb is realistic about her team's work. "The next ten to fifteen years are going to see a lot in the way of new knowledge," she says, speaking of the growth of biotechnology. "But whether or not that will succeed in reaching the field and then the consumer remains to be seen." She cautions that it is very difficult to trace a gene's effect all the way through a plant and modify it effectively for the desired result - "to find the tweak that works." "We're very little babies at this," she says. "It's going to be slow, but I think that's okay. We're learning all the time."
JoAnn Lamb: lambx002@umn.edu
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