Persistence and Yield among Nondormant Alfalfas Selected for Grazing Tolerance

Perennial, warm season grasses are the predominant pasture species in the Coastal Plain of the southern USA. These grasses have two major limitations: (i) an off‐season (normally winter) when they have either limited or no production and (ii) low nutritional value during most of their main growing season. Using nondormant alfalfa (Medicago sativa L.) as supplemental grazing for grass pastures may overcome these limitations because it has a long growing season in areas with mild winters and also has high nutritional quality. However, alfalfa is generally not grazed due to poor stand persistence and grazing‐tolerant cultivars are currently dormant types. Therefore, we used selection for survival after heavy grazing pressure with continuous stocking by beef cattle (Bos sp.) to develop two nondormant, grazing tolerant alfalfa germplasms. These were then tested for survival and forage yield in four experiments of 1 to 2 yr duration under heavy grazing pressure with continuous stocking by beef cattle at Tifton, GA. The selected, nondormant alfalfa germplasms persisted under heavy grazing pressure as well as the grazing tolerant, dormant cultivar, Alfagraze, but were better in respect to plant survival than other nondormant cultivar checks. All entries survived in control areas that were clipped at an early flowering stage. The yield of nondormant cultivars was better from late autumn through early spring than Alfagraze. Some winter damage occurred in 1 of the 4 yr for the nondormant germplasms and cultivars, which did not occur with Alfagraze. Research Question Because of their long growing season and high nutritional quality, nondormant alfalfa scultivars have potential for use as supplemental grazing in the Coastal Plain of the southeastern USA. In this paper, we report the results of breeding and grazing experiments to develop grazing tolerant, nondormant alfalfas for pasture use in this region. Literature Summary Beef cattle are a major agricultural enterprise in the southern Coastal Plain and perennial, warm season grasses such as bermudagrass and bahiagrass are the predominant pasture species used. These grasses have two major limitations: (i) growth ceases in the winter resulting in an “off‐season” lasting up to 120 d and (ii) low nutritional value during most of their growing season. Using alfalfa as supplemental grazing may overcome the limitations of warm season grass pastures. Alfalfa has a long growing season and high nutritional quality. However, alfalfa, whether dormant or nondormant, is typically not used for grazing due to rapid stand loss. The recent development of ‘Alfagraze’ alfalfa, a grazing tolerant cultivar, showed that grazing tolerance could be added as a primary trait to dormant alfalfa. The widespread interest in and use of Alfagraze throughout many parts of the USA showed the importance producers have placed on the grazing tolerance trait. A grazing tolerant, nondormant alfalfa with a capacity for fall and winter production would be desirable in the southeastern Coastal Plain. Study Description We used a selection procedure similar to that used for Alfagraze to develop two nondormant, grazing tolerant germplasms, GA‐FL77‐S2 and GA‐MX. These germplasms were tested for stand survival and yield at Tifton, GA, during four separate experiments using either intensive grazing with continuous stocking by beef cattle or hay clipping management. Applied Questions How did the grazing survival of the nondormant, grazing tolerant alfalfas compare with Alfagraze and other nondormant cultivars? GA‐FL77‐S2 and GA‐MX demonstrated plant survival under grazing equal to Alfagraze but better than the best adapted nondormant cultivar, Florida 77. Their yield and survival under hay clipping management were also similar to the best nondormant checks. What advantage do these nondormant alfalfas have over Alfagraze? Because survival under grazing was similar to Alfagraze, the main advantage of nondormant, grazing tolerant alfalfas was found in their seasonal yield distribution. In areas of mild winters, nondormant cultivars showed higher yield during the late fall through early spring. Improved seasonal distribution of high quality forage suggests the possibility of using these grazing tolerant, nondormant cultivars for year round supplemental grazing in the Coastal Plain. However, winter damage occurred in 1 of 4 yr in stands of nondormant cultivars, which was not seen in Alfagraze. Will seed of GA‐FL77‐S2 and GA‐MX be available to producers? GA‐FL77‐S2 and GA‐MX were released by the University of Georgia under the cultivar names of ABT 805 and AmeriGraze 702, respectively. Recommendation Whenever grazing will be part of a producer's program with alfalfa, it is important to use a proven grazing tolerant cultivar. However, due to the potential for winter damage, it would appear that the best recommendation would be to use grazing tolerant, dormant or semidormant cultivars in areas where winters may be harsh, but grazing tolerant, nondormants in areas of mild winters or where producers are willing to risk winter damage in order to achieve the better seasonal yield distribution advantage of the nondormant cultivars.