Evaluation for grazing tolerance in alfalfa
Bruce, David R. A.
Knowledge of plant characteristics that are associated with grazing tolerance of alfalfa (Medicago sativa L.) would help in the development of cultivars that are tolerant of close continuous grazing. The objectives of this study were to characterize a broad range of cultivars for tolerance to grazing and evaluate these cultivars for traits that have been associated with grazing tolerance within one grazing season. A series of 10 experiments were established from seed (Glenlea, MB; Brandon, MB) or from transplants (Portage la Prairie, MB) and were subjected to either close continuous grazing or rotational grazing with beef cattle. Cultivars were evaluated ground cover, stand density, stem production and decumbency, crown area, crown bud production, secondary root number, crown depth, nitrogen concentration and total nonstructural carbohydrates (TNC) during each grazing season. There were few differences between cultivars for stand persistence after one season of grazing at all locations. There was no ground cover correlation between continuous and rotational grazing in microplots (r = 0.03, p $<$ 0.82) and a low correlation for large plots (r = 0.36, p $<$ 0.0003). Cultivar differences were present for some plant traits (e.g. decumbency, crown bud production), but there was no consistent trend across traits or between experiments. The results suggest that in the short growing season that occurs in western Canada, more than one season of grazing is necessary for the evaluation of alfalfa persistence and plant traits using either seeded stands or transplants.