Jonathan Daniel Richwine

Reduced floral resources and habitat fragmentation have led to pollinator decline. Increased diversity of native plants in pastures could support cattle and pollinators. However, the relationship between grazing and plant diversity needs to be investigated. We explored how grazing rest periods impacted persistence and forage characteristics of Andropogon gerardii (BB)/Sorghastrum nutans (IG; BBIG) and Panicum virgatum (SG) pastures interseeded with forbs and grazed over five years. ANOVA analysis was conducted using R with significance set at p ≤ 0.05. Forb species exhibited different establishment and flowering characteristics. Coreopsis tinctoria, Rudbeckia hirta (BESU), and Coreopsis lanceolata (LCOR) established early, while Helianthus maximiliani, Heliopsis helianthoides (OSUN), and Echinacea purpurea (PURC) established the second season. Rudbeckia hirta, LCOR, OSUN, and PURC flowered most frequently, and the grazing regimen did not influence the flowering frequency of any species. Desmodium tortuosum (TTFL) was one of the most selected by cattle. Total forage mass declined in 2022, but forb mass interacted with treatment and year where mass declined each year but varied among treatments annually. Based on persistence and forage characteristics, BESU, LCOR, OSUN, PURC, and TTFL could successfully provide forage in native pastures under a variety of grazing regimens.

Data are needed to identify optimum response to potassium (K) and phosphorus (P) amendment and associated mycorrhizal colonization for native warm-season grasses (NWSGs; big bluestem [BB; Andropogon gerardii Vitman] and switchgrass [SG; Panicum virgatum L.]). To evaluate these responses, experiments were conducted in Knoxville and Springfield, Tennessee, from 2013 to 2019. In twice-annual harvests, we assessed BB and SG dry matter (DM) yield, crude protein (CP), total digestible nutrients (TDNs), P and K removed by grasses (removal), and soil test P and K in response to P (29 to 88 kg ha⁻¹) and K (70 to 257 kg ha⁻¹) elemental rates, and rates of root colonization by mycorrhizal fungi in response to P. Amendments had no effect (p > 0.05) on DM yield, CP, or TDN for either species. Yield, CP, and TDN fluctuated among years (p < 0.001) for both species, but no consistent temporal trends were observed. Although removal exceeded inputs at the control (no input) for P and K, and at 70 kg K ha⁻¹, there was not an associated reduction in soil test K and P values. Phosphorus rate affected (p = 0.02) total mycorrhizal colonization, with an average of 62% colonization across both species and 70% at the highest P rates. Given the lack of response for yield, CP, TDN, or associated soil nutrient test levels, NWSGs appear to offer a low-input option for forage production.

Pollinator declines and expectations for more sustainable agriculture, including pasture-based enterprises, bring attention to strategies to enhance the habitat value of grazing lands. We evaluated native warm-season grass (NWSG) pastures with (FORB) and without (CONT) interseeded native forbs in 2021–2023. An analysis was conducted using R with the significance set at p ≤ 0.05. The grass appeared to be weakened predominantly by grazing management practices. Forb density and mass had an inverse relationship in seasons two and three. Total forage mass declined in response to increased grazing days and weakened stands. The forage nutritive compositions differed, with more stable, season-long crude protein and lower fiber concentrations in late-season FORB, which supported higher bodyweight gains and season-long average daily gain. Black-eyed Susan (Rudbeckia hirta; BESU), lanceleaf coreopsis (Coreopsis lanceolata; LCOR), and showy ticktrefoil (Desmodium canadensis; STTF) were the most abundant forbs, and BESU, LCOR, and purple coneflower (Echinacea purpurea; PURC) produced long flowering windows. Cattle grazed STTF, cup plant (Silphium perfoliatum; CUPP), and oxeye sunflower (Helopsis helianthoides) the most. Under continuous stocking, a blend of BESU, LCOR, PURC, STTF, and CUPP produced acceptable cattle gains and provided pollinator resources, suggesting that this model may be a viable means to enhance the sustainability of pastures.

Incorporating native forbs within native warm‐season grass (NWSG) pastures has the potential to benefit cattle, pollinators, and wildlife beyond that of NWSG monocultures. However, when grazing NWSG pastures, rotational stocking is recommended as opposed to continuous stocking. Therefore, to evaluate whether within‐season rest is needed for native pasture sustainability, two NWSG grazing experiments were conducted near Greeneville, TN, 2017–2020, to assess the persistence of native forbs when an 11‐species native forb blend was interseeded into established switchgrass (SG; Panicum virgatum L.) and big bluestem/indiangrass (BBIG; Andropogon gerardii Vitman and Sorghastrum nutans (L.) Nash) pastures. Each experiment was a completely randomized design with four replicates of each within‐season rest grazing treatment (no rest, early rest, middle rest, late rest, and no graze). Within‐season rest was not influential for NWSG tiller density or total forb plant density thus indicating persistence of forbs may not require rotational stocking. Purple prairie clover (Dalea purpurea Vent.) did not establish while Illinois bundleflower (Desmanthus illinoensis (Michx.) MacMill. ex B.L. Rob. & Fernald) was only observed flowering once despite having the greatest seeding rate among forbs. Based on establishment and flowering of the 11 species in the current mixture, interseeding a 6‐species polyculture of black‐eyed Susan (Rudbeckia hirta L.), dixie ticktrefoil (Desmodium tortuosum (Sw.) DC.), eastern purple coneflower (Echinacea purpurea (L.) Moench), lanceleaf coreopsis (Coreopsis lanceolata L.), Maximilian sunflower (Helianthus maximiliani Schrad.), and oxeye sunflower (Heliopsis helianthoides (L.) Sweet) could allow for plant biodiversity while offering floral resources for pollinators during the NWSG grazing season.

The identification of appropriate nitrogen (N) rates for native warm-season grasses (NWSG) is needed to inform forage management in the southeastern United States. Experiments were conducted in Knoxville and Springfield, TN, from 2015 to 2019, to evaluate dry matter (DM) yield, forage nutritive value (FNV), the influence of temperature and precipitation on yield, and partial factor productivity (PFP) responses. Three NWSG species (big bluestem [BB; Andropogon gerardii Vitman], switchgrass [SG; Panicum virgatum L.], and eastern gamagrass [EG; Tripsacum dactyloides L.]) were grown at each location and harvested twice annually. Five N rates in the form of urea were applied annually in split applications. The yields for all species responded positively to nitrogen (p < 0.001) and the time of harvest (p < 0.001) at both sites, except for BB yield at Springfield; no consistent N effects were observed over years. Nitrogen affected the FNV (p < 0.001) of all species, increasing CP by three to five percentage points (p < 0.001). Yields across all species and locations responded positively to precipitation (p < 0.001) and temperature (p < 0.001). A moderate N amendment (−1 yr⁻¹, based on PFP) can enhance the productivity of NWSG, but responses were site-dependent and influenced by temperature and precipitation.

Insect pollinators are in population decline due to environmental and chemical stressors. Including native forbs in pastures could benefit grazers and pollinators; however, their forage and flowering characteristics are not fully documented. The objectives of our research were to evaluate 12 native forbs for persistence, forage mass, nutrient composition, and flowering patterns under repeated defoliation. Twelve species were planted in a small-plot experiment in 2018. Response variables were measured from 2020 to 2022. Annual (partridge pea, PPEA, Chamaecrista fasciculata) and biennial (black-eyed Susan, BESU, Rudbeckia hirta) species established high (p < 0.05) plant populations during the first season; however, the PPEA declined (p < 0.05) in forage mass during 2021. Tall species (Maximilian sunflower, MSUN, Helianthus maximiliani; cup plant, CUPP, Silphium perfoliatum) increased in forage mass, produced high-quality forage, and flowered during early fall. Lanceleaf coreopsis (LCOR, Coreopsis lanceolata) produced consistent (p > 0.05) forage mass and flowered in spring. The purple coneflower (PURC, Echinacea purpurea), Illinois bundleflower (ILBF, Desmanthus illinoensis), and oxeye sunflower (OSUN, Helopsis helianthoides) produced high-quality, consistent (p > 0.05) forage mass and flowered mid-season. Interseeding the BESU, ILBF, PPEA, LCOR, PURC, OSUN, and MSUN or CUPP would produce high-quality forage and floral resources throughout summer.