SELECTION WITHIN ALFALFA CULTIVARS FOR PERSISTENCE UNDER CONTINUOUS STOCKING

Alfalfa (Medicago sativa L.) has been predominately used as a hay crop in North America and most cultivars do not persist under grazing. The objectives of this research were to determine if grazing tolerance could be improved within alfalfa cultivars and to determine population shifts that occurred during selection. The original and selected populations of 'Apollo', 'Florida 77', 'Alfagraze', 'Spredor II', and 'Travois' were evaluated in central Georgia under 17 to 22 wk of continuous close grazing by beef cattle for 2 yr. Experiments I and II were comprised of two seasons of continuous close grazing and Exp. III was comprised of two seasons management for hay production. In addition, eight released, multiple-pest-resistant cultivars were also evaluated in Exp. II and III. Stand persistence was measured with plant density measurements and forage production was measured under exclosures. All selected populations, with the exception of Alfa graze, had better stand persistence and yield than their original populations when grazed, but yield and persistence were similar when managed for hay production. Although several fungal pathogens influenced plant mortality there was an inconsistent relationship between disease resistance and stand persistence under grazing. This research indicated that at least two seasons of continuous grazing are required to achieve a consistent ranking for grazing tolerance. In conclusion, this study suggests that grazing tolerance can be improved within existing cultivars without sacrificing forage yield.