- Agronomic: general hay and forage crops
- Animal Products: dairy
- Animal Production: grazing management, grazing - rotational
- Production Systems: agroecosystems
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.
Project objectives:div style="margin-left:1em;">
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.