Performance of Switchgrass and Bluestem Cultivars Mixed with Cool‐Season Species1

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Abstract
Forage availability in summer is critical for sustaining high stocking densities of herbivores on pasture in the eastern U.S. The objective of this study was to determine forage productivity and quality of switchgrass (Panicum virgarumL.) and bluestems [Andropogon gerardiiVitman, Schizachyrium scoparium(Michx.) Nash, and Bothriochloa caucasica(Trin.) C.E. Hubb.] in summer. The experimental site was located in southwestern Pennsylvania on Guernsey silt loam (fine, mixed, mesic Aquic Hapludalf) soil. Two replicates, each containing eight warm‐season grasses with different proportions of volunteer cool‐season grasses and overseeded legumes were grazed from 1975 to 1977 and then harvested for hay in 1978 and 1979. Pastures were grazed each year in mid‐May, late July or early August, and early October. Nitrogen at 0, 45, and 90 kg ha−1and P at 0, 20,40 kg ha−1were applied to subplots. ‘Blackwell’ switchgrass and ‘Kaw’ big bluestem from the Great Plains readily established stands but did not persist as well as cultivars from the eastern USA. Total annual production from switchgrass‐dominated pastures was about 8.0 Mg ha−1and that from ‘NY 1145’ big bluestem was 6.0 Mg ha−1, Over a 4‐yr period, NY 1145 produced about 70% more forage in late July than did Kaw big bluestem. Mean yield distribution of the switchgrass and bluestem pastures was approximately 15% in May, 55% in July‐August, and 30% in October. July yield increased about 11 kg kg−1of N applied. Mean in vitro dry matter disappearance (IVDMD) values for switchgrass and bluestem ranged from 470 to 570 g kg−1,, but it was determined that IVDMD under‐estimated in vivo digestibility by 100 to 200 g kg −1, Crude protein concentration ranged from 70 to 120 g kg−1, Mean crude protein concentration of grass fertilized with 45 and 90 kg N ha−1over a 3‐yr period was 10 and 26% higher, respectively, than that for unfertilized grass. Overseeded legumes, especially red clover (Trifolium pratenseL.), established good stands in warm‐season grasses with < 75% stands. Mixed stands of warm‐ and cool‐season grasses and legumes can be maintained under grazing or hay production, with a substantial shift in seasonal yield distribution that can be very beneficial to beef (Bos taurus) producers.
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