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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 (<135 kg N ha−1 yr−1, based on PFP) can enhance the productivity of NWSG, but responses were site-dependent and influenced by temperature and precipitation. [ABSTRACT FROM AUTHOR]

Heterosis plays an important role in switchgrass (Panicum virgatum L.) breeding. To identify superior clones for hybrid development through seasonal single cut, 10 crosses derived from 'Alamo' × 'Kanlow' and parents were evaluated. The experiment was planted in 2018 using a randomized complete block design with two replications at two locations in Tennessee: the East Tennessee Research and Education Center (ETREC), Knoxville, and the Plateau Research and Education Center (PREC), Crossville. The crosses and their parents were evaluated for biomass yield, plant height, and clonal mass in the fall of 2019 and 2020. The crosses were significantly different in biomass yield within and across locations (P = .05). Average biomass yield of the crosses ranged from 7.1 to 8.7 Mg ha-1 at ETREC and from 10.0 to 11.8 Mg ha-1 at PREC. The crosses demonstrated an average of 46% mid-parent heterosis (MPH) and 24% high-parent heterosis (HPH) for biomass yield across the two locations. The MPH and HPH were 3 and -1.3% for plant height and 12 and 1% for clonal mass, respectively. Moderate to strong positive association was found between clonal mass scores and biomass yield at individual locations across years and across locations and years (r = 0.37-0.79, P = .05). The association between biomass yield and plant height was inconsistent (r = -0.24 to 0.67, P = .05). The findings of biomass yield heterosis in these crosses suggested the potential of hybrid cultivars for biomass yield improvement in lowland switchgrass. [ABSTRACT FROM AUTHOR]

The lack of forage production during the seedling year is a barrier to wide‐scale adoption of native warm‐season grasses (NWSG). To address this, two NWSG establishment experiments were conducted in Knoxville, TN, 2016–2018, to determine the efficacy of big bluestem (BB; Andropogon gerardii Vitman) and switchgrass (SG; Panicum virgatum L.) establishment with browntop millet [BTM; Urochloa ramosa (L.) Nguyen] as a companion crop. Each experiment was a randomized complete block arranged as a 2 × 3 factorial. Two defoliation strategies [(1) harvests based on BTM maturity (boot to heading stage) for hay (HAY) or (2) clipping to control BTM competition by maintaining >50% sunlight reaching BB and SG seedlings (CLIP)] were coupled with three BTM seeding rates [0 (control), 11.2 (half‐recommended rate), and 22.4 (full‐recommended rate) kg pure live seed (PLS) ha−1]. Only BTM seeding rate affected BB and SG plant density at dormancy. In all cases, the control had greater BB and SG plant density than the full‐recommended rate, indicating that BTM impeded BB and SG establishment. All BTM seeding rates resulted in acceptable stands (≥5.4 plants m−2) of BB (both years) and SG (2017 only). Only the control allowed for acceptable stands of SG in 2016 (8.5 plants m−2). Managing BTM for HAY produced a mean cumulative dry matter (DM) yield of 3.15 and 2.68 Mg ha−1 in 2016 and 2017, respectively. These findings show that BTM can be a companion crop that helps offset production losses during BB and SG establishment. Core Ideas: Browntop millet nurse crop may offset lost forage production during big bluestem or switchgrass establishment.Recommended browntop millet seeding rate reduced big bluestem and switchgrass establishment.Half millet seeding rate had minimal effect on big bluestem and switchgrass establishment.Millet cutting regimes did not affect big bluestem or switchgrass establishment success. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a warm-season, perennial grass valued as a promising candidate species for bioenergy feedstock production. Biomass yield is the most important trait for any bioenergy feedstock. This study was focused on understanding the genetics underlying biomass yield and feedstock quality traits in a "Kanlow" population. The objectives of this study were to (i) assess genetic variation (ii) estimate the narrow sense heritability, and (iii) predict genetic gain per cycle of selection for biomass yield and the components of lignocelluloses. Fifty-four Kanlow half-sib (KHS) families along with Kanlow check were planted in a randomized complete block design with three replications at two locations in Tennessee: Knoxville and Crossville. The data were recorded for two consecutive years: 2013 and 2014. The result showed a significant genetic variation for biomass yield (p < 0.05), hemicellulose concentration (p < 0.05), and lignin concentration (p < 0.01). The narrow sense heritability estimates for biomass yield was very low (0.10), indicating a possible challenge to improve this trait. A genetic gain of 16.5% is predicted for biomass yield in each cycle of selection by recombining parental clones of 10% of superior progenies. [ABSTRACT FROM AUTHOR]