Abstract
Effects of transplanted seedling density and species on sward structure of native warm-season grass (NWSG) stands were compared in a randomized complete block design. About 6-week-old NWSG (big bluestem (BB, Andropogon gerardii Vitman), eastern gamagrass (GG, Tripsacum dactyloides L.), indiangrass [IG, Sorghastrum nutans (L.) Nash] and switchgrass (SG, Panicum virgatum) seedlings were transplanted in 45-cm wide rows on clean-tilled seedbeds. Within-row spacing was 30, 25, or, 20 cm giving 10, 12, and 15 plants m-2 as low, medium, and high seedling density, respectively. During establishment, the stands were allowed uninterrupted first year growth without fertilizers or irrigation but when necessary, tall-growing broadleaf weeds were mechanically removed. In the following spring, all dead standing biomass was mowed down to allow emerging tillers access to sunlight. During the second year after planting, early-spring basal diameters, row-length intercepted by the NWSG crowns, mid-summer sward heights, and percentage bare ground were determined. From the second June after planting, and for two consecutive years, plots were harvested twice year-1 to assess forage biomass. Data showed that, unlike species, seedling density had no effect on the assessed parameters. Cumulative forage biomass, in kg DM ha-1, was the least for GG (4901) at low and the most (18,245) for SG at high seedling density during the second year. Corresponding values for the third year were 4500 and 7799 kg DM ha-1. Basal diameters ranged from 18 cm (BB) to 24 cm (IG) while percent row intercepts were from 6 (GG) to 46 (IG) with sward heights measuring 41 cm (IG) to 54 cm (GG). In each stand, percent ground cover by the NWSGs, and at every seedling density, averaged 60.5. Transplanting at ≥10 plant m-2 resulted in harvest-ready stands by the second year of establishment. And while close spacing favored the NWSGs against weeds, data showed that an initial plant density of >10 plants m-2 may not result in increased forage production worthy the additional establishment cost. Data on response to fertility management and forage quality attributes are necessary for more reliable practical recommendations.
Highlights
In the Southeast United States, frequent mid-summer forage shortages, have made livestock producers more interested in the potential ability of native warm-season grasses (NWSGs) to increase forage productivity of their pasture systems
Wildlife feed availability may vary with the actual litter biomass present due to its effects on soil moisture retention and invertebrate populations as previously reported [16] [17]. These results show that transplanting BB, GG, IG or SG, reducing the plant density from 15 to 10 seedlings m−2 does not have significant effect on the early-stand forage biomass production
In year 2, the forage biomass for SG was similar to IG and consistently greater than BB and GG, yields in year 3 remained more or less stable for the latter pair but decreased notably for the other
Summary
In the Southeast United States, frequent mid-summer forage shortages (summer slump), have made livestock producers more interested in the potential ability of native warm-season grasses (NWSGs) to increase forage productivity of their pasture systems. Despite the unique abilities of NWSGs to remain productive during extended hot dry summers, most livestock producers are yet to confidently incorporate them into their forage systems due to uncertainties associated with their establishment. This is so because NWSG establishment is difficult, costly in both time and resources, and initial stands often exhibit poor performance. Factors like low germination percentage and/or emergence, seed dormancy, low seedling vigor and survival, and severe weed competition, negatively impact the success of NWSG establishment These factors necessitate research to seek faster establishment methods for NWSGs and avail information for their early integration into summer forage systems
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