Reducing Nitrogen Fertilizer Inputs to Irrigated Pastures and Hayfields by Interseeding Legumes

2011 Annual Report for OW10-309

Project Type: Professional + Producer
Funds awarded in 2010: $49,849.00
Projected End Date: 12/31/2012
Region: Western
State: Colorado
Principal Investigator:
Joe Brummer
Colorado State University

Reducing Nitrogen Fertilizer Inputs to Irrigated Pastures and Hayfields by Interseeding Legumes


Suppressing grasses with glyphosate prior to interseeding resulted in the most consistent legume establishment. Close mowing to simulate heavy grazing generally did not result in improved establishment. Of the five legumes evaluated, alfalfa established the best in the glyphosate treatment in Colorado, increasing yield by over a ton per acre. In Idaho, establishment was more variable, with red clover establishing well regardless of suppression treatment. No legumes established in Oregon due to heavy rodent activity. This study highlighted the importance of suppressing the existing grasses and choosing a vigorous legume species for interseeding to reduce the risk of seeding failure.

Objectives/Performance Targets

The overall objective of this project is to demonstrate to producers how legumes can be interseeded into existing grass-dominated pastures and hayfields, thereby increasing the quantity and quality of forage produced, while reducing nitrogen fertilizer inputs. Both on-farm demonstration and small plot trials will be used to achieve the following specific objectives:

Objective 1 – Evaluate the establishment success of various legume species, including alfalfa, birdsfoot trefoil, red clover, white clover and sainfoin, interseeded into grass-dominated pastures and hayfields, with and without mechanical, herbicidal and/or animal suppression of the existing vegetation.

Objective 2 – Evaluate the effects of introducing legumes into grass-dominated pastures and hayfields on forage yield and quality compared to fertilizing the existing grass-dominated stand with nitrogen.

Objective 3 – Using inputs of seed, herbicide, fertilizer, labor, machinery, etc. associated with objective 1 and yield and quality outputs from objective 2, conduct a basic economic analysis comparing pastures or hayfields that have adequate (>20% by weight) legume composition to straight grass stands fertilized with nitrogen.

Objective 4 – Disseminate results of this project to other producers through such means as field days, workshops, conferences, on-line reports and other media and the production of a how-to manual.


In spring 2011, frequency of legume occurrence was sampled at all sites. No legumes were found in the small plots at the Oregon site due to heavy rodent activity the previous year. Suppression of the existing grasses with glyphosate was the only treatment that allowed for establishment of all five legume species at the Colorado site (Table 1). Alfalfa was the most successful with a frequency of 73% in the glyphosate treatment. Birdsfoot trefoil, red clover and sainfoin were intermediate with an average frequency of 33%. Even though white clover had the lowest frequency of occurrence, it will be able to spread over time due to its stoloniferous growth habit.

Unlike the Colorado site, results from Idaho were more variable (Table 1). Glyphosate did not stand out as the best suppression treatment. Averaged across legume species, frequency of occurrence was essentially the same between direct interseeding and suppression with glyphosate. Red clover and birdsfoot trefoil established well in the direct seeded plots with an average frequency of 33%. In the mowed plots, red and white clover established well. Alfalfa and red clover performed the best in the glyphosate treated plots. Red clover was definitely the most vigorous of the legumes seeded at the Idaho site, establishing well in all three suppression treatments with an overall average frequency of 39%.

A possible reason for the differential response among suppression treatments at Idaho compared to Colorado was that a different type of interseeding drill was used. Although the John Deere Powr-till drill does not disturb a lot of the existing vegetation, it does remove some of the roots in a narrow band (~3/4 of an inch) that the seed is dropped into. A double-disk opener drill with leading coulters like the Great Plains only slices the sod, which has little effect on suppressing the existing vegetation.

Although there were no legumes that survived at the Oregon site in the replicated small plot trial, there were some that did survive in an adjacent larger-scale demonstration area. In the glyphosate treated area, birdsfoot trefoil stood out as the best with a frequency of occurrence of 30%. Only minor amounts of alfalfa (2%) and white clover (3.5%) were present. Red clover was present but did not show up in any of the frames. In the mowed area, only minor amounts of white clover (2%) and birdsfoot trefoil (4%) were present. Unlike the small plot area, this area was exposed to grazing during the establishment year. Although grazing with its associated hoof action can lead to injury and death of seedlings, it also keeps the overstory shorter, which reduces light competition. Legume seedlings become spindly and yellow if they are under light stress for too long. Seedlings in this condition are very tender and often die once the overstory is removed, and they are exposed to harsher environmental conditions.

The main benefits of interseeding legumes into grass-dominated stands are increased forage yield and quality and a reduced need to apply nitrogen fertilizer. At the Colorado site, very few legumes established in the direct seeded or mowed treatments (Table 1), and this was reflected by no increase in yield (Table 2). Alfalfa established well in the glyphosate treatment and increased yield by over 2,000 lbs/ac compared to the unfertilized control. The grass-alfalfa mix even out yielded the control fertilized with 80 lbs N/ac by over 700 lbs/ac. Red and white clover and birdsfoot trefoil that established in the glyphosate treated plots had an intermediate effect on yield, falling between the unfertilized and fertilized controls. Even though sainfoin established well in the glyphosate plots (Table 1), the plants were small, did not compete well with the grasses and did not contribute to total yield.

As indicated above, establishment of the various legumes in relationship to the suppression treatments was quite variable at the Idaho site (Table 1). Red clover established well across all three suppression treatments, and this was reflected by increased yield in those plots. In the glyphosate treatment, the grass-red clover mix yielded over 1,600 lbs/ac more forage compared to the unfertilized control. Generally, the better a particular legume established, the greater the impact on total yield. Just like at the Colorado site, sainfoin did not perform well at the Idaho site.

Samples were collected to measure forage quality, but we are still in the process of completing those analyses at the time of this report. We anticipate a significant increase in quality in those treatments where the legumes established well.

In addition to the plots and demonstrations established in 2010, the small-plot trials were replicated in spring 2011 at each site. This will allow us to test the effects of environmental variability between years on legume establishment, as well as obtain data from Oregon due to complete failure of the seeding in 2010.

Data collection (frequency of legume occurrence, yield and forage quality) will be repeated at all sites in 2012 in both the small-plot and demonstration trials. Tentatively, a field tour is planned at each site during summer 2012 to view and discuss findings from the project. A fact sheet on interseeding legumes will be drafted in 2012.

Impacts and Contributions/Outcomes

Results from this study (first full year of production) were presented at the Western Alfalfa and Forage Conference held on December 11-13, 2011 in Las Vegas, Nevada. Approximately 700 people were in attendance at that meeting. In addition to the presentation given at the meeting, a paper summarizing the results was included in the proceedings.

For producers interested in interseeding legumes into their grass dominated hayfields and pastures, this study emphasized the need to suppress the existing vegetation prior to seeding. The use of glyphosate herbicide resulted in the most consistent establishment. In addition to suppressing the existing vegetation prior to seeding, it is also important to choose a vigorous legume like alfalfa or red clover to reduce the risk of seeding failure. Although establishment tends to be variable following interseeding, once legumes are established, they contribute significantly to both forage yield and quality, thereby reducing the need for nitrogen fertilization and improving the overall economics of forage production.


Dr. Glenn Shewmaker
University of Idaho
Twin Falls Research and Extension Center
P.O. Box 1827
Twin Falls, ID 83303
Office Phone: 2087363608
Mark Campell
Jeld-Wen Timber & Ranches
401 Harbor Isles Blvd.
Klamath Falls, OR 97601
Office Phone: 5418857466
Edwin Smith

44 Dry Gulch Road
Hansen, ID 83334
Office Phone: 2084239117
Dr. Chanda Engel
Oregon State University
Klamath Basin Research and Extension Center
3328 Vandenburg Rd.
Klamath Falls, OR 97603
Office Phone: 5418837131
Jack Whittier

4880 E County Road 64
Wellington, CO 80549
Office Phone: 9705687170
Laura Hooper
2225 South 1200 E
Bliss, ID 83314
Office Phone: 2088374950
Curtis Bridges

2364 County Road 62
Wellington, CO 80549
Office Phone: 9705687501