Symbiotic Nitrogen Fixation and Establishment of Six Montana Montana Native Legume Species

Plant Materials Technical Note Number MT-54

If you encounter any problems with the file provided on this page, please contact Technical Resources at 406-587-6822.

A printer-friendly version of this technical note is available in Adobe Reader format.

Plant Materials Technical Note Number MT-54 (PDF; 99 KB)

February 2006.
By Sarah Metcalf, Master of Science Graduate in Land Rehabilitation, Montana State University; Clain Jones, Assistant Research Professor, Department of Land Resources and Environmental Sciences, Montana State University; and Larry Holzworth, NRCS Plant Materials Specialist, Bozeman, Montana.

Abstract

Legume species have been known to affect soil nitrogen content and are incorporated into land restoration seed mixes to improve degraded soils and vegetative communities. The goals of this project were to improve native legume establishment methods as well as to determine the overall soil benefits from six individual native legume species: Astragalus canadensis, Dalea candida, Dalea purpurea, Hedysarum boreale, Lupinus argenteus, and Vicia Americana. Seeds planted into three soils without inoculant in the greenhouse, indicated that field soils contained Rhizobia spp. specific to most of the species, due to evidence of nodulation. In a follow-up field experiment, plants were harvested after two growing seasons at three sites. Shoot biomass at each field site varied significantly; in general, A. canadensis had the highest biomass, while D. purpurea and D. candida had the lowest biomasses. This research showed that native legume inoculum may be present in the soil for establishing these six species and that seed treatment fungicides were generally detrimental to legume seedling establishment.

Management Conclusions

In order to better utilize soil resources and minimize weed competition, plant species within a community should be selected for habitat adaptation and diversity. Species with different growth and root morphologies will improve the structure and function of a plant community. Diversity not only reduces species competition and optimizes resource utilization, it can also reduce the risk of large population losses due to pests or disease.

Long-term survival is improved with a mosaic seeding pattern rather than rows, to create patches and give each species space to obtain natural growth forms. Broadcasting seed over stubble rows at Moccasin, Montana was highly effective in reducing weed invasion and may have increased seedling emergence by providing protection against environmental elements.

Successful establishment of native legume and grass mixtures requires special cultural techniques. Species with faster more aggressive growth habits, such as grasses, should be seeded at a lower rate and in a different or alternative row, a minimum of 12 inches from the slower growing species. Seeding and inoculation is best in the early spring and will increase seedling survival and decrease the time for nodulation, as compared to a fall seeding. Inoculation can be beneficial in some cases; however, in most of the soils tested, inoculation was not necessary for nodulation to occur.

Elevated levels of N in the soil have been shown to repress nodulation, but it has also been shown that fertilizers can increase overall legume production. Grass legume mixture compositions can be maintained by a proper nutrient balance of nitrogen and phosphorus. Phosphorus favors legume vigor whereas nitrogen stimulates grass growth. The first few seasons of growth are critical to establishing a sustainable plant community. Amendments such as fungicides, fertilizer and inocula may benefit seedlings in establishment and should be considered based on site conditions and soil tests. However, beneficial soil biota such as rhizobia and mycorrhizal fungi can be harmed by fungicides. Controlling weeds and invasive species is important during the two growing seasons due to the slow establishment of native legumes. Proper timing for planting and establishment is crucial to long-term success of a plant community.

There is a large degree of variability in establishment success even within a species, because each plant can respond differently to a given environment (see Table 7, Native Legume Characteristics). Overall, these species are hardy and often fairly tolerant of drought and grazing. Once established, native legumes require little maintenance and are capable of re-seeding themselves, persisting, and complementing a plant community.

The following pictures show alternate row legume grass plantings establish full complements of each species within a mixture.

Utah sweetvetch (Hedysarum boreale)	Alfalfa (Medicago sativa)

* Data from USDA NRCS National Plant Database
** From study data
*** I = indeterminate, D = determinate

< Back to Plant Materials Technical Notes

Last Modified: 08/21/2008