Benefits of increasing grazing height on weed suppression in grass based grazing systems

Final Report for GNC09-114

Project Type: Graduate Student
Funds awarded in 2009: $9,199.00
Projected End Date: 12/31/2010
Grant Recipient: University of Wisconsin
Region: North Central
State: Wisconsin
Graduate Student:
Faculty Advisor:
Dr. Mark Renz
University of Wisconsin
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Project Information

The benefits of increasing grazing height on weed suppression in management-intensive rotational grazing systems in Wisconsin

While the goal of Extension personnel is to ensure research findings are disseminated to the public, often obstacles that hinder adoption are not clearly understood. In pastures many factors limit adoption of new research including research conducted at research facilities exclusively. This often limits interaction and collaboration with private farmers and can reduce adoptability of new practices. We conducted weed suppression experiments on research farms and private farms to evaluate how similar the results would be. While private farms had a yield advantage when compared to research farms, differences between treatments were similar. Working with private and research farms in combination with electronic surveys and focus groups were found to be a sufficient tools to address both the awareness of research as well as obstacles that prevent adoption of new weed suppression methods in pastures.


Weedy pastures have been shown to have reduced forage quantity, quality, and utilization by animals (Seefeldt, Stephens, Verkaaik, & Rahman, 2005). Although herbicides exist to manage these weeds many land managers avoid applications due to cost of application, impact to desirable legumes in their pasture, and banned use in organic pastures. Increasing the residual grazing height is one management option that could become an effective option for weed management in pastures in the upper Midwest. Research has shown that increasing the residual grazing height from 5 cm to 15-20 cm can suppress common pasture weed seedling density by 61-67% (Schmidt & Renz, 2010a, 2010b) in management-intensive rotational grazing (MiRG) systems.

However, this prevention was associated with a significant loss in forage quantity, when compared to common grazing practices in pastures in the upper Midwest. A focus group was conducted in the fall of 2009 to address concerns over forage yield reductions with weed management methods. The group designed two additional treatments to test in 2010 to mitigate forage loss, while still obtaining adequate weed suppression (Schmidt & Renz, 2010a). As farmer adoption of agronomic practices is dependent on many factors (Doll & Jackson, 2009; Pannell et al., 2006) we wished to determine what threshold of yield loss would prevent adoption of weed management methods by surveying MiRG farmers. Others have shown that participatory on-farm research can yield different results compare to research farms (Bell, Lyon, Gratton, & Jackson, 2008; Jackson, Bell, & Gratton, 2007). We wanted to determine if these differences were evident with weed suppression methods in MiRG systems in the upper Midwest. Specifically, the objectives of this paper are to evaluate if weed suppression methods involving increasing residual grazing heights are practical to adopt on farm and if results were similar between research farms and private farms. Additionally, we wished to survey MiRG farmers about weed management methods currently utilized to direct future research.

Project Objectives:

Expected short-term outcomes will develop an understanding of how producers can balance suppression of weed seedling emergence with potential reductions in forage yield and quality by altering grazing heights. These outcomes will be directed towards the members of the focus group.

Intermediate outcomes will include the extension of this information to grazing networks and sustainable agriculture organizations as well as publication in peer reviewed journals. This information will include a discussion of the mechanisms we determined to suppress weed seedling emergence and how it can be applied to a range of grazing production systems (e.g. beef production, sheep production, dairy).

Long-term outcomes include a better understanding of how to use cultural practices to not only prevent weed emergence, but balance this prevention with forage quantity and quality. This research also has the potential to be useful in other areas where weed seedling suppression is desired, such as restorations in natural areas, or weed management for programs such as Conservation Reserve Program (CRP).


Click linked name(s) to expand/collapse or show everyone's info
  • Mark Renz
  • Marie Schmidt


Materials and methods:


In the summer of 2010 we conducted an electronic e-mail survey of MiRG farmers throughout Wisconsin and Minnesota to determine adoptability of our research regarding weed seedling suppression. We designed a questionnaire in conjunction with University of Wisconsin Cooperative Extension Information Technology. Information on weeds, weed management, pasture management and forage quantity were collected. Before distributing the survey, it was sent to 3 Wisconsin farmers to ensure clarity of questions. The survey was distributed via e-mail listserve in August 2010 to the Grassworks, Inc., a Wisconsin-based organization of MiRG farmers and the Center for Integrated Agriculture Systems at UW-Madison. Respondents were sent an e-mail containing a link to the survey and reminder e-mail was sent one week later.

Research vs Private Farm

Yield was measured at 2 research farms and 2 private farms in 2008-2009 and at 2 research farms and 3 private farms in 2009-2010. Forage biomass was measured at each grazing event by collecting forage from four randomly placed 0.125-m2 quadrats in each plot. Within each quadrat forages were harvested to the treatment height, collected, dried, and weighed to determine yield for various treatments and timings (Schmidt &amp; Renz, 2010a). We used this data to compare yields between research farms and private farms. Differences in productivity between research and private farms were detected using SAS ANOVA proc mixed, at a p-value <0.05. Weed suppression could not be compared between sites, as private farms did not want additional weed seed spread into active pastures.

Research results and discussion:


According to the survey (n=47), the dominant methods of weed management utilized in MIRG pastures in the upper Midwest are clipping and grazing with 89% and 70% of MiRG farmers using these methods, respectively. Herbicides were also used by 32% of farmers, but only by spot spraying, not broadcasting. Our study focused on utilizing grazing management that includes leaving residual grass in fall during the last grazing event of the year. When asked to what residual height farmers graze in the fall, 25% graze to 5 cm, 59% grazed to 10 cm and 16% leave greater than 15 cm of residual height. Although this response indicates typical residual heights are lower than those that suppress weed populations, 79% of those who responded would be willing to leave 15-20 cm of residual height in the fall to suppress 50% of weed seedlings the following year. This indicates that MiRG farmers would be willing to adopt practices that would increase weed suppression in certain situations.

Another concern about adoption of increased residual grazing heights for weed suppression is the reduction in forage. Previous research has indicated the loss in forage in the last grazing event in the fall can range from 0-70% (Schmidt &amp; Renz, 2010a, 2010b) In the survey we specifically asked respondents about residual grazing heights and potential forage loss in the last fall grazing event of the year. Survey data show that 45% of farmers would be willing to sacrifice 1-20% of forage, 34% of farmers would be willing to sacrifice 21-40% of forage and 14% of farmers would sacrifice 40+% during their last fall grazing event. This method appears to be best suited for pastures that experience high weed pressure as one farmer would be willing to graze, “a portion of the farm lower in the fall, but this could be altered year to year,” alleviating some concern over forage loss in the fall. Clearly increasing residual grazing heights will be of interest to MiRG farmers under some situations in the upper Midwest.

Total Yield Results Compared

Private farms were more productive than research farms studied between 2008-2010 (Table 1). The private farms yielded 42% and 58% more total biomass in 2008-2009 and 2009-2010, respectively. While differences in productivity existed between farms, differences between treatments were similar between farms and no interaction between farm and treatments were detected. While others have found differences between research farms and private farms and attributed the differences to historical management, farmer knowledge and environmental gradients (Chambers, 1994; Kloppenburg, 1991), benefits of controlled facilities can allow for research to be conducted that would not be allowed on private farms (e.g. addition of weed seeds). An additional benefit that we observed by conducting research on private farms was improved visibility of the experiment. This may result in improved adoption of practices as several pasture walks were conducted at experiment locations.

Participation Summary

Project Outcomes

Project outcomes:

This study demonstrates that holding focus groups and utilizing surveys can increase awareness of obstacles to adopting new weed management techniques such as increasing residual grazing heights. Also, making use of local stakeholders for research direction encourages participation in the research process and improves awareness of research methods. This study also demonstrated that data collected on research farms can differ, but differences between treatments were similar in this situation. Both research farms and private farms are valuable for research. For example, we could not have collected weed data without access to research facilities, while employing private farms to host university research we not only encouraged local participation, but also can resolve any yield discrepancies between farms. The survey permitted us to ask questions that will direct future weed science research as well as increase local farmer’s awareness of new weed management techniques. Finally, many comments in the survey emphasized the fact that management decisions are not always centered on maximum production, but can often be related to weather, economics, accessibility or seasonality.


Areas needing additional study

Future Research Needs

A pest management survey was conducted that asked crop consultants and farmer cooperatives to identify problem weeds in pastures (Renz, 2006). However, this survey was not inclusive of MiRG farmers who do not usually rely on these groups for weed management. In order for us to understand the management decisions of MiRG farmers, we asked if this group were concerned about the three most common weeds identified in the crop consultant survey. Respondents were most concerned about Canada thistle, with 75% reporting it as a problem, while only 43% and 30% considered plumeless thistle and burdock problem weeds in their pastures, respectively. Differences in concern may be associated with specific livestock, as some farmers mentioned that cows eat burdock when it is young, but sheep producers were especially concerned, as its fruit can attach to wool and reduce its value.

In addition to using the survey and focus group to compare research farms with private farms and reconcile any differences, we were interested in using the results to direct future research in weed management. The on-line survey was set up in such a way that there was an option of leaving a comment for questions. This allowed the respondents to clarify answers as well as pose questions about the research. For example, several farmers mentioned that Canada thistle is more often a problem in newly established pastures or pastures that are managed less intensively. Other farmers expressed a high level of interest in using this research in areas where livestock will be out-wintered as weed pressure the following year can increase due to the heavy disturbance and concentrated nutrients, “We've had increased thistle problems, the following year, where bales were set-out as an out-wintering area. I would need to have made that decision to leave those fields 15-20 cm tall, at the START of the grazing season.” Other methods of weed control that were mentioned included: biological control, manual digging of thistles and burdock, burning, crop rotation and high density stocking combined with long rest periods. Finally, whole farm management includes decisions based on many factors and a farmer’s goal may change depending on the requirements of the livestock. For example, it was mentioned that “15-20 cm height in spring would interfere with frost seeding,” or “sometimes mud and calving pressures overrule what is best for my grazing plan.” Directing research towards these specific situations in developing other weed management methods will be beneficial to MiRG farmers and likely increase adoption.

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.