Exploring an Explorer's Old Idea; Improve Semiarid Grasslands with Yellow-Flowered Alfalfa

Specifically, SDSU scientists are exploring whether yellow-flowered alfalfa can improve the quality of grazing in pastures of crested wheatgrass. Crested wheatgrass is a non-native, cool season grass that offers livestock good nutrition early in the year but isn’t as nutritious or palatable as temperatures warm during the summer.

Niels Ebbesen Hansen, a longtime botanist at what is now South Dakota State University as well as a self-styled “plant explorer” for the U.S. Department of Agriculture, first introduced yellow-flowered alfalfa to North America. He made eight journeys through Europe and Asia to search for plant material and is famous for finding or developing some 350 varieties of fruits, vegetables, trees and other crops.

Hansen collected seed of yellow-flowered alfalfa, Medicago falcata, already during his first expedition in 1897-98. He gathered large amounts of the seed during later expeditions in 1906, 1908-09 and 1913. He found yellow-flowered alfalfa that was adapted as far as northeastern Siberia, where it was able to endure temperatures in the range of 85 degrees below zero. That suggested to Hansen it would probably thrive on the dry, cold northern Plains — “my American Siberia,” as Hansen called it.

As early as 1909, in an inventory of plants he had recently brought back from abroad, Hansen suggested yellow-flowered alfalfa could be introduced into native pastures.

More than a century later, SDSU graduate student Chris Misar said a variation of that idea is the crux of his research. He and his professors want to know whether interseeding hardy, yellow-flowered alfalfa into crested wheatgrass pastures can allow the alfalfa to get established and bolster the nutrition available to livestock.

Ironically, crested wheatgrass is another plant introduced to North America by N.E. Hansen after he saw it at the Valuiki Experiment Station on the Volga River in Russia on a journey for the U.S. Department of Agriculture in 1897-98. But it would be decades before the grass came into wide use.

“Crested wheatgrass was not widely utilized until the 1930s and later,” Misar explained. “Crested wheatgrass was planted on many acres of abandoned cropland and degraded rangeland in the west and Great Plains for revegetation purposes. The grass saved a lot of soil from wind erosion due to its ability to grow and protect soil when environmental conditions were poor.”

Funding for SDSU’s yellow-flowered alfalfa research has come through sources such as the South Dakota Agricultural Experiment Station, the Five-State Ruminant Consortium and USFS Grand River National Grassland.

In addition, Misar was awarded a $9,060 grant from the North Central Region Sustainable Agriculture Research and Education Program for the interseeding project earlier this year as part of NCR-SARE's Grad Student Grant Program. Misar is carrying out his study in plots near Fruitdale and Buffalo in South Dakota, as well as Hettinger, N.D., and Newcastle, Wyo. He’s evaluating seeding date, seeding rate and sod suppression using herbicide as factors that all can influence the success of interseeding yellow-flowered alfalfa into crested wheatgrass.

Because it’s a legume, yellow-flowered alfalfa is able to fix nitrogen through nodules in its root system, enriching the soil for the crested wheatgrass. It also sequesters some carbon and provides additional habitat. And it’s able to flourish in locations that, in Misar’s study, receive an average 13 to 15 inches of annual precipitation. However, the challenge is getting alfalfa seedlings successfully established in crested wheatgrass stands.

Associate professor Lan Xu in SDSU’s Department of Biology and Microbiology, one of Misar’s advisers, said because both yellow-flowered alfalfa and crested wheatgrass have been established on the Northern Plains for a century now, there’s no question that both plants can survive dry, cold conditions. For example, it’s known that N.E. Hansen provided seed to Lodgepole, S.D., rancher Charles Smith in 1915, and the plant has been established in northwestern South Dakota since then.

“He introduced it nearly 100 years ago and it’s never disappeared,” Misar said. “That’s our motivation to study it — it’s been so persistent. Alfalfa that can survive in Siberia can survive here.”

SDSU range scientists also know, from studying yellow-flowered alfalfa on the Grand River National Grassland, that yellow-flowered alfalfa won’t spread wildly — it prefers fine-textured soils and moist conditions such as the low ground in swales.

“What we have learned is that yellow-flowered alfalfa has not become naturalized to the extent sweetclover and leafy spurge have on rangelands. Its distribution, including soil seed bank, is very confined,” Lan Xu said. “Plus it has incredible value as an agricultural crop.”

Lan Xu noted that naturalized yellow-flowered alfalfa found on the Grand River National Grassland is not pure Medicago falcata. It probably hybridized with purple alfalfa, Medicago sativa, in nature through pollination.

SDSU researchers also have studied the volume of seed that yellow-flowered alfalfa produces under natural conditions and have explored why its seed doesn’t germinate uniformly and readily. Lan Xu said the simple explanation is probably that it is a survival mechanism — a built-in means of staggering germination so that at least some plants are likely to encounter the conditions that allow them to come to maturity.

Diane Narem received an $1,800 Schultz-Werth Award for the outstanding research paper she wrote at SDSU as a student of Lan Xu studying that topic. Narem also was the recipient of Joseph F. Nelson Undergraduate Research Mentorship to conduct the seed germination research project. Her study probed the effects of stratification, warm treatment, and mechanical and acid scarification on the emergence of yellow-flowered alfalfa. Greater than 99 percent of yellow-flowered alfalfa seeds from the soil were viable but less than 4 percent germinated under standard laboratory conditions. The objective of the research was to determine if low germination rate was due to physical or physiological seed dormancy.

“What we have learnt from Diane’s study is the emergence rate of yellow-flowered alfalfa seeds can be significantly improved by scarification treatments, particularly sandpaper treatments. It indicated the low germination rate is most likely due to physical dormancy,” Lan Xu said. “This plant comes from Siberia. It has adapted to that very harsh and unpredictable environment so that it doesn’t all germinate at once.”

Yet another study is exploring how various alfalfa populations transplanted to the Antelope Range Research Station near Buffalo, S.D., stand up to cattle grazing over multiple growing seasons.

As Misar wraps up his master’s degree study, and as some other SDSU research continues, producers will get a better picture of what is necessary to get yellow-flowered alfalfa established in crested wheatgrass pastures, and how to include the forage in their grazing programs.