Motivations for restoring tallgrass prairie in the Upper Midwest range from natural resource conservation to developing new forage and cropping systems. Cropping systems based on the tallgrass prairie may be well-suited to meeting several needs on and off farms, including: reliable summer forage for livestock; biomass feedstocks for producing home heating fuels, electricity, and ethanol; and wildlife habitat and ecosystem services such as reducing nutrient flows to water and sequestering carbon in healthy soils. The primary objective of this project is to evaluate the potential for restored prairies to provide summer forage under rotational grazing management.
Non-native cool-season (C3) grasses and legumes have been the preferred forage system for grass-based livestock systems in the north central United States, but these pastures can suffer from a slump in productivity and quality during warm, dry summers. Incorporating pastures dominated by native, warm-season (C4) grasses has been proposed as a means to compensate for the short-term and long-term effects of summer slumps, but basic research and farmer adoption remains limited. This study compared switchgrass monocultures and prairies planted with native C4 grasses, native legumes, and native forbs to investigate relationships between plant diversity and forage availability and nutritive value. In addition, we interseeded a suite of native legumes into these existing grasslands. We hypothesized that: increased native legume abundance would be correlated to higher forage yield and nutritive value; and disturbance during the growing season (managed grazing or mowing) would increase native legume recruitment. However, we observed very poor legume recruitment across all diversity levels and disturbance treatments.
Overall, nutritive value of forage harvested from reconstructed native grasslands was suitable to meet the dietary needs of non-lactating cattle across the diversity treatments. Cattle tended to avoid consuming native forbs and avoided foraging for palatable species interspersed within dense patches of native forbs, which significantly reduced forage availability in diverse prairies relative to switchgrass stands. Mean forage yield at the paddock scale was twice as high for switchgrass than for diverse prairies. Across diversity levels, mowed and undefoliated control plots differed significantly in plant community composition during both years, but grazed and control plots did not differ. Native grasslands with high abundance of tall-statured native forbs may be less suitable for adoption in production systems due to impacts on forage availability, but vulnerability of C4 grass monocultures to weed invasion following defoliation suggests that functional group diversity may be useful for limiting shifts in community composition to support high forage yields over longer time periods.
The potential benefits and tradeoffs of high biodiversity in grazing lands have been explored for cool-season grass-legume pastures of the temperate United States, but it is unknown if the positive relationship between diversity and productivity found in tallgrass prairies in the North Central U.S. is maintained when herbivores are added to the system.
In humid to sub-humid environments, cool-season (C3) grasses are very productive, but season-long carrying capacity can be reduced when peak growth occurs by mid-June. An important component of this region’s natural history is the tallgrass prairie ecosystem, a mid-continent grassland in which warm-season (C4) grasses produce the majority of above- and belowground biomass. Dominant species include Andropogon gerardii Vitman (big bluestem), Panicum virgatum L. (switchgrass), and Sorghastrum nutans (L.) Nash (Indiangrass).
The advantages of C3 and C4 grasses can be captured when managers plan to graze non-native and native pastures in sequence: at the beginning of the grazing season, animals are stocked on C3 pastures; then, in early summer, animals are stocked on pastures dominated by C4 grasses to utilize rapid vegetative growth (allowing C3 pastures longer rest periods), and, finally, animals remain on C3 pastures from late summer through fall after C4 grass productivity and quality have declined. In the North Central U.S., sequential grazing with C3 and C4 pastures has previously been evaluated in Iowa, central Wisconsin, and southwestern Michigan.
C4 grasses utilize the C4 photosynthetic pathway, generally resulting in inherently lower forage quality due to low digestibility of leaf structure and reduced levels of nitrogen-rich photosynthetic enzymes compared to the C3 pathway used by cool-season. Growing a mix of native forbs and legumes with C4 grasses may improve productivity and N concentrations compared to growing C4 grasses alone. Pairings of C4 grasses and native legumes in small plot studies demonstrated improved forage quality and production for some pairings, and several native legume species have been evaluated for forage quality and productivity. However, no published research exists that documents the effect of these species in pastures, or their persistence in a rotational grazing system in the upper Midwest.
Identify scientifically sound pasture management techniques to promote establishment of native legumes within warm-season grass stands.
Determine whether incorporating native legumes into an existing prairie will provide a significant forage production benefit.
This study was conducted at the Wisconsin Integrated Cropping Systems Trial (wicst.wisc.edu/) located at the UW-Madison Arlington Agricultural Research Station in southern Wisconsin. Native grassland reconstruction at WICST began in 1999. The primary goal was to restore native plants and a natural process (fire) to restore ecosystem function and provide baseline conditions for comparison with crop and forage systems. The 1999 prairie restoration (WICST Prairie) was implemented as a randomized complete block design with three diversity treatments randomly assigned within each of three blocks: 1) a low diversity (LD) prairie seed mix including six native species, 2) a high diversity (HD) prairie seed mix including 26 species (the LD complement and an additional 19 species), and 3) a control, continuous corn (CC) planted and harvested annually. The species sown in these treatments are native species found in mesic tallgrass prairie communities and represent several functional groups (Table 1). The prairie seed was hand broadcast and cultipacked in June 1999, and subsequent management included periodic clipping for weed control from 1999-2002. The CC treatment concluded in 2006; in June 2007 the CC plots were planted with switchgrass (cultivar: Forestburg) to include a native C4 monoculture (SW) treatment. The grasslands were burned in 2003, 2005, and 2008. During this study, the grasslands were burned again in 2009 and 2010. Canada thistle has been treated with spot application of herbicide during the growing season.
Plant community diversity, management, and legume interseeding treatments were were applied in a hierarchical split-split plot design. Diversity treatments served as whole plots in the nomenclature of split plot design. Each whole plot was split into three subplots to apply management treatments: grazing, mowing, and control. Due to requirements of the grazing treatment (fencing and supplying water), this split was applied at the block level, with control subplots located in the southern position, and grazing and mowing subplots randomly assigned to the northern or central positions. To account for this spatial arrangement, we also included these management blocks as a random factor in statistical analyses. Management treatments subplots were split into sub-subplots for native legume interseeding. Sub-subplots were randomly assigned interseeding or no interseeding treatments. This experimental design resulted in 54 experimental units, with 18 experimental units in each block and six experimental units in each diversity treatment (Fig. 1). Each experimental unit measures 55 ft by 45 ft m, covering approximately 0.1 acre. All experimental units were burned annually in the spring from 2008-2010.
Rotational grazing: Six Holstein heifers were used in the managed grazing treatment. In June, each animal weighed approximately 500 pounds, and the animal unit equivalents (AUE) for the herd were estimated at 3.0 and 3.6 for June and July grazing periods, respectively. Area of individual paddocks was 0.1 acres. Animals were moved to a new paddock when herd managers observed that the majority of C4 grasses were grazed to a residual height of approximately 6 inches, and we recorded time spent on each paddock.
Mowing: Mowing was completed using a rear-mounted, PTO-driven, rotary deck mower, an implement used by a wide range of land managers. The mower deck was adjusted to leave a residual vegetation height of 15-20 cm, which was similar to the residual height of grazed C4 grasses observed in this study’s grazing treatment and the typical height selected for weed control in establishing prairies. Mowing could not be completed at the same time as grazing due to possible disturbance to the cattle and was carried out following the completion of grazing treatments.
Five legumes were selected for their potential utility to grazing farmers in the Upper Midwest: Amorpha canescens Pursh. (lead-plant), Desmanthus illinoensis Michx.) MacMill. ex B.L.Rob. & Fernald (Illinois bundle-flower), Desmodium canadense (L.) DC. (showy tick trefoil), Lespedeza capitata Michx. (round-headed bush-clover), and Dalea purpurea Vent. (purple prairie-clover). Interseeding occurred on June 26, 2009, following completion of the June grazing and mowing treatments. Five native legume species were incorporated into a mixture and seeded at a rate of 100 seeds per square meter (20 seeds per species). Prior to planting, each species was inoculated with appropriate Rhizobium bacteria to promote healthy growth of legume seedlings. Interseeding was accomplished using a Great Plains no-till drill, an implement designed for interseeding in grasslands with minimal soil disturbance.
Native legume recruitment was estimated in August-September 2009, June 2010, and August 2010 using seedling counts. Five 0.5 square meter quadrats (a 1 m by 0.5 m frame) were located in each experimental unit. The frame was wider than five rows of the no-till interseeding implement. In each quadrat, native legume seedlings rooted inside the quadrat were identified to species and species counts were recorded. In June 2010, quadrats were again randomly located, and the northwest corner of each quadrat was marked with a large plastic stake. The same quadrat locations were revisited in August 2010. The Central Region Seedling Identification Guide for Native Prairie Plants (Missouri NRCS, 2005) provided adequate information to identify native legume seedlings used in this study to species.
Vegetation was harvested to estimate standing biomass and available forage quantity and quality. In June 2009, we estimated standing biomass and available forage using five 0.1 square meter quadrats randomly located in each experimental unit. Within each quadrat biomass was clipped to ground level. Spring prescribed fire removed the previous year’s standing stems and litter. Biomass was sorted into palatable and unpalatable fractions, based on observations of which species cattle were selecting while grazing in switchgrass and prairie stands in the acclimation paddocks. Forage yield and nutritive value were estimated using the palatable fraction of subsamples.
In 2009, we found that high dispersion of unpalatable species caused cattle to avoid selecting sparse, short-statured palatable plants located within stands of tall-statured native forbs. For 2010, biomass and forage sampling methods were altered to reflect cattle behavior. Forage availability and nutritive value was estimated using clippings obtained from feeding stations–patches of palatable vegetation which cattle selected for grazing from the heterogeneous sward.
Forage yield at the paddock-level scale was estimated for each experimental unit by multiplying the mean forage yield at the feeding station scale by the mean frequency of feeding stations. The frequency of feeding stations in each experimental unit was estimated using stratified random sampling. Five subsamples were located approximately 2 meters apart along 5 transects spaced 3 meters apart (25 subsamples per experimental unit). At each subsample location, a 0.25 square-meter quadrat was placed at canopy level and the cover of palatable species was visually estimated. Each subsample with greater than 50 percent cover of palatable species was counted as a feeding station. Frequency was calculated by dividing the number of feeding stations counted in each experimental unit by the total number of samples taken.
All biomass was dried at 60°C to constant weight. Forage samples were ground in a mill until dry matter passed through a 2 mm screen. Samples were analyzed for forage quality by near infrared reflectance spectroscopy (NIRS). Crude protein (CP), neutral detergent fiber (NDF), and relative forage quality (RFQ) were estimated using the mixed grass equation from the NIRS Forage and Feed Testing Consortium and WinISI II Version 1.50 software (Infrasoft International, LLC, Port Matilda, PA).
Differences in recruitment to seedling stage were not ecologically significant because few seedlings were observed surviving to maturity. Mean recruitment to the seedling stage was highly variable among species (Table 1).
Due to the lack of native legume seedling recruitment, data from paired interseeded and not-interseeded plots was combined and averaged. Due to the change in methods used, here we present results from 2010 only.
In 2010, crude protein levels were lower for switchgrass than diverse prairies in both June and July (Fig. 4), reflecting more advanced development in switchgrass in 2010. Neutral detergent fiber was higher in switchgrass than prairies across both months. Relative forage quality was similar across diversity treatments in June, and dropped for both prairies and switchgrass in July. In July, relative forage quality was lower in switchgrass than prairies, reflecting minimal switchgrass defoliation by June grazing and advanced developmental stage in mid-summer (Table 2).
Due to the lack of native legume seedling recruitment, data from paired interseeded and not-interseeded plots was combined and averaged. Due to the change in methods used, here we present results from 2010 only.
Feeding stations were observed more frequently in switchgrass than diverse prairies. At the feeding station scale (0.25 square-meter), forage yield was significantly higher in switchgrass than diverse prairies. Results were similar at the paddock scale: forage yield was significantly higher in switchgrass than diverse prairies. However, mean standing biomass—the total aboveground biomass of the grasslands—was similar across switchgrass and the diverse prairies (Figure 2), indicating that productivity of diverse prairies and switchgrass monocultures was similar.
Given the forage quality of the native prairies and the minimal impact that grazing had on the plant community, the WICST manager continued to practice sequential grazing of these prairies, and the prairies were grazed in 2011-2012 following the completion of the research presented here. This site continues to serve as an example of managed grazing in prairies for grazing groups and other groups visiting WICST. The research conducted in 2009-2010 can serve as a baseline for long-term study of managed grazing in restored prairies.
In 2012, the project coordinator has received requests for data and project results from Organic Valley, which is considering the potential for using native warm-season grasses in mixed rations for grass-based dairy systems. In southwestern Wisconsin, the Wisconsin Department of Natural Resources (WiDNR) and the Wisconsin Department of Agriculture, Trade and Consumer Protection are working with several partners to develop a program to match owners of native grassland with graziers in search of additional pasture, and the qualitative and quantitative results of this project will be used by partners to inform both audiences.
Farmers who are interested in experimenting with establishing native legumes or prairies should remain flexible in their planting plans due to variation in supply and demand and may need to consider postponing establishment for another year or more. Prices of native legume seed can fluctuate widely. The price of one of the most promising native legumes identified for forage production and establishment (Canada tick-trefoil) was approximately $60 per pound in spring 2009; in fall of 2012, the price was approximately $300 per pound due to extreme drought and poor seed production. Consequently, the cost per acre for seeding would have increased from $15 per acre to $70 per acre at the seeding rate in this study (approximately 0.25 pounds per acre).
This project was first proposed in 2008, and over the life of the project, grass-based animal products have become more visible in the media and the marketplace due to consumer interest in perceived benefits to product quality, human health, farm viability, animal welfare, and natural resource conservation. However, if consumers are interested in further differentiation to identify grass-based products that sustainably use native grasslands, the level of demand remains small. At this time, there are no labels identifying products derived from native grasslands, and individual farmers/farm enterprises would be responsible for differentiating their product and educating consumers about the characteristics of native grasslands and the value of native grasslands for the farm and the landscape.
Given the lack of legume recruitment we observed, at this time farmers in the north central U.S. are unlikely to adopt native legume interseeding for native grasslands.
While this specific practice is unlikely to be adopted in the short-term, this project illuminates the potential of native grasslands to be utilized for summer forage for appropriate classes of livestock. Native grasslands established for wildlife conservation by public or non-governmental organizations have the potential to incorporate livestock grazing to meet management objectives, and native grasslands established on farmland (through the Conservation Reserve Program or other efforts) have the potential to be brought into production rather than converted to other crops.
In the short- to intermediate-term, farmer adoption of native grasslands for grazing in the north central region will likely be limited to utilization of grasslands originally protected or reconstructed for conservation goals. Conservation leaders are increasingly recognizing that private landowners and the sustainable use of working lands play a critical role in meeting goals for grassland conservation and restoration: the scale of most preserves is simply too small to protect viable populations of many native plants, insects, birds, and mammals. In turn, conservationists are increasingly reaching out to collaborate with farmers on grassland conservation.
We hypothesize that as farmers begin to gain experience with these plant communities via partnerships with prairie conservationists, they will develop new ideas and methods for utilizing native grasslands and begin to work more closely with neighbors who own such grasslands or begin to establish prairie pastures or hay plantings on their own farms.
Educational & Outreach Activities
- Spring 2009 – poster at UW-Madison Spring Ecology Symposium
Fall 2009 – approximately 30 graziers and grazing specialists from southeastern Wisconsin attended a pasture walk discussing research goals and demonstrating initial response of native grasslands to grazing and mowing
Summer 2010 – approximately 30 graziers from south central Wisconsin attended a pasture walk; hosted evening pasture walk for 5 members of The Prairie Enthusiasts; reached out to the Wisconsin NRCS state grazing coordinator, Wisconsin DATCP organics/grazing coordinator, and ecological restoration interns at The Aldo Leopold Foundation for tours
Winter 2011 – approximately 30 graziers, grazing specialists and natural resource professionals from around Wisconsin attended a presentation on research objectives, methods, and results at GrassWorks annual conference
Summer 2011 – approximately 40 ecologists from across the U.S. attended a presentation on research objectives, methods, and results at the Ecological Society of America’s annual conference
Fall 2011 – reached a key audience of US Fish & Wildlife Service and Wisconsin Department of Natural Resources staff through seminar hosted by The Aldo Leopold Foundation; M.S. exit seminar reached an audience of UW-Madison faculty, staff and students representing the departments of agronomy, agroecology, and environmental studies as well as staff from the USDA Dairy Forage Research Center
Spring 2012 – approximately 20 conservationists from south central Wisconsin attended a presentation of research objectives, methods, and results at the annual board meeting of the Sauk Prairie Conservation Alliance (invited presentation)
- 2010: “Forage Production and Quality of Restored Prairie Interseeded with Native Legumes,” in 12th Technical Report (2007 & 2008). Available online at http://wicst.wisc.edu/
2012: “Managed Grazing in WICST prairies: Tradeoffs Between Plant Functional Diversity, Forage Availability, and Resistance to Weed Invasion,” in 13th Technical Report (2009 & 2010). Available online at http://wicst.wisc.edu/
Areas needing additional study
The trends in plant community composition observed in this study suggest that management of eastern tallgrass prairies can incorporate grazing by cattle without resulting in degradation—an important result that contradicts a deeply entrenched opinion among the conservation community (which holds that cattle destroy prairies). The widespread negative impacts of historic grazing regimes likely stemmed from high stocking rates, continuous stocking, and lack of fire.
At the same time, the results of this project demonstrate that we still lack important knowledge about how to manage prairies sustainably with grazing or other agricultural methods, particularly haying. While data was not collected in 2012, the extreme drought conditions demonstrated that native warm-season grasses do not produce abundant growth during severe droughts—these species are able to survive droughts, but like many traditional forage species, these native grasses have adapted to survive through slowed growth and dormancy. During years with slight to moderate reductions in summer precipitation, native warm-season grasses may provide an important summer forage source, but these species are not dependable under the most dire conditions. This experience calls into question our working hypothesis that restoring native warm-season grasses to farms in the north central U.S. will aid in resilience to periodic drought and changing climates.
- More than 200 species of forbs occur in prairie and savanna habitats in Wisconsin, but there has been little to no research to screen species for forage quality and productivity, anti-quality secondary chemicals, and re-growth following defoliation by grazing or haying. Our knowledge of herbivory tolerance is primarily inferred from observations of the frequency and abundance of forbs in historically-grazed prairies.
Given the documented forage quality of native legumes, researching methods for establishing native legumes in new or established warm-season grasslands deserves more attention, with methods that will support decision-making about the timing of interseeding and follow up management.
Farmers in the north-central region are experiencing a trend toward longer growing seasons and milder climates, and warm-season grass cultivars are adapted to similar conditions at lower latitudes; these cultivars should be evaluated for the upper Midwest because the adaptation to longer growing season could provide improved forage productivity and greater resistance to weed invasion.
Many restored prairies in the north-central region are threatened by invasion of native and non-native shrubs and trees; haying may be a useful tool for limiting shrub invasion, and research is needed to understand the potential for shrub control, return on investment for farmers, and effects on plant communities and grassland bird populations.
With few farmers integrating warm-season grasslands into their operations, we continue to lack knowledge about whole farm management and how warm-season grasslands impact the farm as a system. Having a small proportion of pasture land devoted to C4 grasses (10-25 percent) could make it easier to manage the rapid growth of cool-season pastures following spring emergence from dormancy. Reducing the proportion of cool-season pasture used by a grazing operation could facilitate increased utilization of rapid early growth rates and reduce the need for mechanical forage management such as haying or post-graze clipping. In addition to providing summer forage, incorporating prairie restorations into grazing operations may provide an additional benefit to farmers by reducing demands on C3 grasses during periods of water- and temperature-stress during mid-summer. Overall animal performance and farm profitability may be improved by providing opportunities to decrease the intensity of summer defoliation on cool-season stands to increase rest periods and ultimately support higher vigor of the cool-season stands—which graziers typically rely upon to provide high-quality forage in the spring for lactating animals as well as in the fall for finishing grass-fed beef.
Direct marketing and values-based value chains may provide opportunities for farmers who utilize diverse native grasslands to differentiate their products based on positive ecological attributes associated with their products.