Prairie Restoration: Effects of Burning, Herbicide, and Nitrogen Manipulation to Reduce Invasive Cool-Season Grasses

Final Report for GNC10-130

Project Type: Graduate Student
Funds awarded in 2010: $9,978.00
Projected End Date: 12/31/2010
Grant Recipient: SDSU
Region: North Central
State: South Dakota
Graduate Student:
Faculty Advisor:
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Project Information

Project Completed!

Native tall-grass prairies in the United States were once found on about 400 million acres. Now, less than 3% of their original expanse exists. Farming, loss of natural disturbances (fire and grazing), and introduced exotic plant species have contributed to this reduction. Invasive exotic plants, which have often been introduced purposefully, out-compete native species and reduce native diversity and productivity. Native species abundance and productivity can be increased when released from competition by human intervention and/or if natural processes, such as fire, are reintroduced to the ecosystem.

In this study, two South Dakota field locations containing mixed native and non-native aggressive species will be treated with fire, chemical, and/or nitrogen applications at various times during critical growth stages of the species of interest in order to reduce the presence and productivity of invasive species and stimulate native species. Native species in field plots include big bluestem (Andropogon gerardii), sideoats and blue grama (Bouteloua curtipendula and B. gracilis) whereas the predominant invasive species includes smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis). A greenhouse project that complements the field study examines the influence of shoot and root competition on establishment and growth among these native and invasive species. Leaf area, root and shoot biomass, and perennating structure formation will be evaluated by species.

For land managers and producers, relatively inexpensive steps can be taken to enhance the native species component of pasturelands with the use of prescribed burns, appropriate timing of herbicide application, and modest applications of fertilizer. These steps would sustain and increase native grass species biomass, increase forage production, improve wildlife habitat, and decrease the need for weed management in surrounding croplands. The objective of this study was to evaluate the use of fire, herbicide and nitrogen applications to reduce non-native cool-season grass species competition and biomass while increasing native warm-season grass species biomass at a low cost and straightforward for land managers and producers as a step towards restoration of pasture or infested grasslands.

Project Objectives:

Short term outcomes: Identify and quantify grass species located at two sites prior to application of treatments, apply spring and fall treatments and follow the outcomes of the treatments through the following growing season(s), determine vegetative growth rates of native vs invasive species alone and in combination in field and in greenhouse studies, and compare root and shoot growth rates of species of interest alone and in combination in the greenhouse under warm and cool temperatures.

Intermediate outcomes: Examine the treatment effects on competition and determine treatments or treatment combinations that would be effective management tools to reduce invasive cool-season grasses, and improve native grass composition. Inform producers about the effective treatments through meetings, field days, and publications.

Long term outcome: Producers and land managers have affordable management methods other than large scale herbicide applications to improve pasture conditions by reducing introduced invasive grass and encourage more native grass populations for improved forage and aesthetic quality.


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  • Dr. Sharon Clay


Materials and methods:

Two sites, Artesian and Volga, were selected for this experiment. Eastern South Dakota is characterized by periodic droughts and wind advisories during the hot summers and cold snowy winters. Summers experience occasional high temperatures at 32.2 oC and winter temperature extremes can dip below -17.7oC without the addition of a wind chill. Average annual precipitation range from 63.5-76.2cm. In the year 2010, precipitation was 54% above the 30 year average.

This site is located near Artesian (N 44° 5.80', W 97° 54.56') in Sanborn County. It is used for haying and pasture. The pastureland has had no prescribed burning, herbicide, or fertilizer application over the past 25 years. The soil type is predominantly Houdek-Dudley complex (fine-loamy, mixed Typic Argiustolls and fine, mixed Typic Natrustolls) with a 0-9 percent slope (NRCS 2010). The ecological site description is glacial till loamy claypan with thin uplands and wet meadows. The dominant species include big bluestem (Andropogon gerardii Vitman), sideoats grama (Bouteloua curtipendula (Michx.)(Torr.)), little bluestem (Schizachyrium scoparium (Michx.) Nash), Kentucky bluegrass (Poa pratensis L.), and smooth brome (Bromus inermis Leyss.).

The Volga site (N 44°23'1.53", W 96°57'29.39") is rangeland owned by South Dakota State University in Brookings County. This acreage has not been harvested, burned, or extensively treated with herbicide. Spot spraying to control musk thistle (Carduus nutans L.) was observed in 2009, no other treatments had been observed. The dominant soil type is Buse-Poinsett complex (fine-loamy, mixed Typic Calciudolls and fine-silty, Calcic Hapludolls) with 2-10 percent slope (NRCS 2010). Site ecological description is thin loamy with shallow marshes and wet meadows. Dominant grass species includes smooth brome, Kentucky bluegrass, big bluestem, and sideoats grama.
Treatments were applied as a randomized split-block split-plot design with four replications. The main effect plots measured 6m by 12m and were split into four subplots (6m by 3m). Main effect treatments included prescribed fire, herbicide application , and nitrogen application. Fire main effect subplots had N timings of April, June, October, or no N. Nitrogen main effect subplots had timings of April, June, October followed by April (double application), and the control. Herbicide main effect was applied in October with no N, May herbicide with no N, April N followed by May herbicide or May herbicide followed by June N.

The study was established in the summer of 2009. After one year of treatment (August 2009 to August 2010), a second location at the same site was established following the same procedure used at location 1. In the second year of treatment (August 2010 to August 2011) at location 1, each plot was halved allowing for a recovery plot. The recovery plots (3m by 3m) received no treatments while the other half continued to receive prescribed treatments.

Data Collected:
*vegetation sampling
*soil sampling
*light quality and quantity
*spring burn temperature

Statistical analysis processed through SAS using both PROC MIXED and PROC GLM.

Research results and discussion:

In tallgrss prairie, dominate species include big bluestem, little bluestem, and sideoats grama. These species are benefited by late spring burns (Towne and Owensby, 1984). Prescribed burns remove the litter layer, allowing light to reach the soil surface; this increases the amount of light newly emerged plants receive (Hulbert, 1988). At both Artesian and Volga, spring burns did increase warm-season species biomass. Volga benefited with two years of spring burns without N whereas warm-season species at Artesian responded immediately to fire treatments without N. Recovery plots had continued increased warm-season species biomass at both sites when a spring burn did not include N application. Fire reduced cool-season non-native species biomass after two years of spring burns without the addition of N at both sites. Artesian responded with decreased cool-season grass biomass after only one spring burn. Forbs were most increased with two years of spring burns at both sites.

Non-target species are of special concern when using herbicide to alter species composition within the tallgrass prairie. Previous studies sited reduced species composition, soil carryover causing damage months after application, and leaching as concerns with herbicide use (Tyser et al., 2004, Alister and Kogan, 2004, Kohl et al., 1994). However, studies have shown October herbicide application and low application rates will reduce cool-season species without harming native desired plants (Anderson, 1994 and Masters et al., 1996). During this experiment, one year of October applied glyphosate at 2.27 kg/ha after warm-season species senescence suppressed cool-season species at both sites. Forb biomass increased from the fall spraying as well.

Vinton and Goergen (2006) state that smooth brome may have a competitive advantage over native tallgrass species due to increased efficiency to cycle N. This may increase the persistence of smooth brome due to N deposition by anthropogenic land use. Results from Volga are similar to Vinton and Goerge (2006) findings. Cool-season grass biomass was increased compared to the control when no herbicide or fire. Nitrogen treatments alone increase cool-season presence. Prescribed burning has been shown to reduce plant available N (Risser and Parton 1982). Throughout this experiment, the application of N was not found to increase warm-season species of interest during the first or second year. Biomass of cool-season species at both sites was reduced by October applied N followed by a spring burn after two consecutive years. This may have been a consequence of N invigorated cool-season growth followed by nearly complete defoliation in the spring.

The results of this experiment suggest that late season herbicide applied after warm-season senescence is nearly as effective as spring burns to reduce cool-season non-native grass species. Additional study is needed to determine if the combination of herbicide and spring burns would ultimately increase the native component of prairie pasturelands in eastern South Dakota.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Poster presentations: WSSA Feb 2010, MNWIIS Nov 2010, WSSA Feb 2011
Oral Presentation: South Dakota Academy of South Dakota Spring 2011

Project Outcomes

Project outcomes:
  • The owner of the pasture at Artesian was pleased with the results.
    Poster presentations: WSSA Feb 2010, MNWIIS Nov 2010, WSSA Feb 2011
    Oral Presentation: South Dakota Academy of South Dakota Spring 2011
    Greenhouse competition study completed
    Multiple meetings with producers at Artesian (informal)
    Field day held in mid-Sept 2011
    Forage and aesthetic quality at both sites improved

Economic Analysis

The cost of treatments was not analyzed. The ammonium nitrate used requires special licensing. The herbicide (Round-up) is fairly inexpensive. Burning only requires fuel and fire so cost is low. Time involved for all treatments is fairly low. The fire treatment would require proper timing, good weather, and notifying the local fire department but a few helpful neighbors could potentially assist with the burn.

Farmer Adoption

The owner of the pasture at Artesian was pleased with the results. He has mentioned that he would like to use spring burns on his pasture to increase the big bluestem presence as he does not appreciate the smooth brome stands. The Volga site is owned by SDSU and further study has been planned. Currently, a study is being conducted to determine the amount of carbon that is being taken in by the prairie.

Educators involved with field day activities have suggested that spring burns and/or herbicide treatments would be excellent means to improve native prairie. I have suggested additional research is needed to combine fire and herbicide treatments. This may be continued at the Volga site.


Areas needing additional study

Additional study is needed to determine if the combination of herbicide and spring burns would ultimately increase the native component of prairie pasturelands in eastern South Dakota.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.