Incorporating native C4 grasses into pastures dominated by C3 grasses can augment tallgrass prairie restoration efforts while improving pasture production. We examined grazing and burning disturbances to promote the establishment of native C4 grasses sown in fall and spring into existing C3 pastures. A second objective was to test the role of resource availability on C4 grass establishment by manipulating inorganic nitrogen (N) availability within each seeding time and management treatment combination. We drill seeded three C4 native prairie grasses (Andropogon gerardii Vitman [big bluestem], Panicum virgatum L. [switchgrass], and Sorghastrum nutans (L.) Nash [Indiangrass]) into an existing C3 grass pasture and applied combinations of disturbance (grazed or burned) and soil amendments (carbon [+C], ambient [N0], nitrogen [+N]) treatments. We monitored native grass recruitment within these treatments over a 3-year period (2005 through 2007). Whereasnative grasses established under rotational grazing, higher recruitment was observed with annual burning. There were periods of N immobilization with C addition, but we observed no benefit to native grass recruitment. Native grasses did not establish under N addition, irrespective of disturbance and seeding, and were not affected by seeding time. Regression tree analyses showed that the best predictor of native grass density in 2006 and 2007 was belowground net primary production in 2006, which was greater under burned plots in 2006 but did not differ between C addition and ambient soil N treatments. This research demonstrates that burning facilitates and nutrient enrichment inhibits native warm-season grass reintroduction and establishment into non-native cool-season grass dominated pastures.
We combined burning and rotational grazing in an effort to promote persistence of recently established native grasses. The experiment took place on a farm in south-central Wisconsin on a cool-season grass pasture that was drill seeded with native warm-season grasses: big bluestem (Andropogon gerardii), Indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum). We used a split-plot experimental design to assess native grass persistence under varying disturbance treatments (burned, burned-grazed, and grazed). We used a paired t-test to determine if the difference between 2006 and 2007 native grass density was significantly different from zero. Native grass tiller density increased under the burned (202%) and grazed (186%) treatments, but not the burned-grazed (29%) treatment. However, the actual native grass tiller numbers in 2007 were much higher in the burned-only than the grazed-only treatment (80 ± 10 tillers/m 2 and 2 ± 1 tillers/m 2 , respectively). We found no loss to native grass tiller density when rotational grazing was applied to plots in the first year after two years of grazing exclusion with burning. In addition, we found that native grass cover was greatest in the burned treatment but not significantly different in the burned-grazed and grazed treatments. Our results suggest that the combined use of burning and grazing as a management tool for native grass persistence in pastures may be possible with deferred grazing during the establishment phase, but alternative timing, intensity, and types of grazing animals should be tested.
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