The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council.

Wednesday, January 30, 2008 - 9:20 AM

Evaluation of Conventional and RoundupReady® Grazing Tolerant Alfalfa Cultivars in the Deep South USA

Jimmy R. Parish1, Jane A. Parish2, Allen S. Hubbard2, Richard H. Watson3, Rocky Lemus1, and Joe H. Bouton4. (1) Plant and Soil Sciences, Mississippi State University, P. O. Box 9555, Mississippi State, MS 39762, (2) Animal and Dairy Sciences, Mississippi State University, P. O. Box 9815, Mississippi State, MS 39762, (3) Forage Improvement, AgResearch Limited, Cnr Springs Rd & Gerald St, Private Bag 4749, Christchurch, New Zealand, (4) Forage Improvement Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401

Use of alfalfa as a grazing crop has been limited in the Deep South USA by poor adaptation to predominantly acidic soils, disease and insect pressure, inadequate persistence under grazing, and weed competition. The advent of Southeastern adapted grazing tolerant alfalfa lines, combined with the insertion of RoundupReady® (RR) technology into these lines, could make alfalfa a widely used forage throughout the Southeast. The objective of the study was to compare the performance of RR grazing tolerant alfalfa cultivars with conventional cultivars under grazing pressure in the Southeastern environment. During the Autumn 2005, plots (1.8 x 4.5m) of seven cultivars of alfalfa (four conventional and three RR cultivars) were no-till drilled into dormant bermudagrass in a randomized complete block design with six replicates.  Pre-grazing and post-grazing samples were taken at each grazing to determine herbage mass production.  Weeds were controlled throughout the study in the RR and conventional cultivars with Roundup and recommended herbicides, respectively.  Alfalfa cultivars were well-established by the spring of 2006, however, due to the unusually arid Spring, grazing was delayed until June and three subsequent grazing periods were accomplished.  Alfalfa DM yields were affected by a grazing date x cultivar interaction (P < 0.0274).  Cultivar differences were observed in June and October 2006, with Alfagraze 600 RR the superior yielding cultivar.  RoundupReady® cultivars were superior (P = 0.0004) in yield to the conventional cultivars during the October harvest. Yield differences are likely related to weed competition in the conventional cultivars.  The conventional cultivar, Amerigraze 702, and the experimental conventional germplasm NF-OK, had comparable (P > 0.05) DM yields to the RR cultivars.  Alfagraze 600 RR was superior (P = 0.0013) to Alfagraze, which indicates RR technology may improve performance of the Alfagraze cultivar and may further broaden the use of alfalfa across the Deep South USA.