Grazing tolerance of cool-season grasses planted as seeded sward plots and spaced plants

Improved grazing tolerance is often an important goal in grass breeding programs. The objective of this research was to compare grazing tolerance of several cool-season perennial grasses planted as seeded sward plots and spaced plants. Cultivars or populations of smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), wheatgrass species (Thinopyrum spp.; Pascopyrum smithii (Rydb.) A. Love), tall fescue (Festuca arundinacea Schreb.), and hardinggrass (Phalaris aquatica L.), were evaluated at Burneyville and Ardmore, OK, for 2 and 4 yr, respectively, as seeded sward plots and spaced plants. Following establishment, plots were grazed heavily (average of 6400 kg live weight ha(-1)) by cattle (Bos spp.) during spring and summer. Grazing tolerance was estimated each fall using survival as well as recovery scores for spaced plants and stand for seeded sward plots. Genotype x environment (G x E) interactions were prevalent, with the Burneyville site being more stressful for grass growth. Within an environment, recovery scores and survival of spaced plants were very similar, with rank correlations exceeding 0.81 (P < 0.05). As plantings became older, entries responded more similarly to heavy grazing across planting arrangements, with rank correlations between stand and survival exceeding 0.70 (P < 0.01) in some cases. 'Barton' western wheatgrass and 'Paiute' orchardgrass were consistently among the most and least grazing tolerant entries, respectively, regardless of planting arrangement. Thus, where seed supplies are limited, initial screening of accessions as spaced plants for 2 to 4 yr should allow breeders to identify cool-season grass germplasm that is potentially grazing tolerant. Subsequent evaluations in sward plots at multiple locations would be helpful in determining which populations to incorporate into a breeding program.