Management Effects on Productivity of Alfagraze Alfalfa-Tall Fescue Mixtures

Persistence and productivity of grazing-tolerant ‘Alfagraze’ alfalfa (Medicago sativa L.) grown with endophyte-free tall fescue (Festuca arundinacea Schreb.) is not well known. Our primary objectives were to determine yield and persistence of the grass and legume in mixture and monoculture with and without N fertilizer at three Georgia locations over 3 yr. Small-plot field experiments with four replications harvested at 4-wk intervals were conducted at Blairsville in the mountains on a Clifton clay loam (clayey, mixed, mesic Typic Hapludults) and at Eatonton in the lower Piedmont on a Davidson loam (clayey, kaolinitic, thermic, Humic Paleudult). The five treatments were ‘AU Triumph’ tall fescue with 0 N; tall fescue with 50 lb N/acre in September, February, and April; tall fescue and Alfagraze alfalfa with 0 N; tall fescue + alfalfa with 50 lb N/acre in February; and alfalfa alone, all harvested at 4-wk intervals. At Athens in the Piedmont on Cecil sandy clay loam (clayey, thermic, kaolinitic Typic Hapludult) the same treatments were harvested at 3-, 4-, and 6-wk intervals. Alfagraze alfalfa persisted well and was productive in mixture with AU Triumph tall fescue with 0 N, averaging about 8000 lb/acre dry forage at the three locations when cut at 4-wk intervals over 3 yr. During the third year, alfalfa constituted 50% or more of the mixture by estimate at 4- and 6-wk cutting invervals and greater than 25% at the 3-wk interval with no additional N fertilizer. Alfalfa monoculture and tall fescue-alfalfa mixtures without N fertilization had similar annual yields, which were superior to grass monoculture with 150 lb N/acre except at Athens where unfavorable soil conditions hindered alfalfa growth. Nitrogen fertilization (50 lb N/acre) of mixtures increased total yield but did not affect percentage alfalfa in the forage. Summer production of alfalfa was superior to tall fescue. Results suggest that Alfagraze alfalfa adequately fertilized with P and K can be successfully grown with endotype-free tall fescue when harvested at 3- to 4-wk intervals, suggesting good persistence under rotational stocking with livestock. Research QuestionMajor advantages of a grass-alfalfa mixture are reduced bloat potential, fewer weed problems, and a more uniform seasonal distribution of yield. A major problem of alfalfa in grass mixtures is stability of stand and production, especially with frequent defoliation or N fertilization. The present study evaluated persistence and productivity of grazing-tolerant alfalfa and endophyte-free tall fescue in mixture and monoculture with and without N fertilizer at three Georgia locations. Literature SummaryFrequent cutting or grazing of hay-type alfalfa cultivars consistently reduces stand, but the Alfagraze cultivar is tolerant of this treatment in monocultures. In mixtures with hay-type cultivars, infrequent cutting favors alfalfa domination while more frequent defoliation favors grass. Information on persistence and productivity of Alfagraze in grass mixtures is very limited, especially when N fertilizer is applied to improve grass production in late winter. Study DescriptionYield and persistence of ‘AU Triumph’ tall fescue and Alfagraze alfalfa treatments (Table 1) were evaluated at three locations over 3 yr. Experiments were harvested at 4-wk intervals at Blairsville (2300 ft elevation) and Eatonton (490 ft). The same treatments were harvested at 3-, 4-, and 6-wk intervals at Athens (980 ft). Harvesting was done from late March to November. How did N fertilization affect the mixtures? Application of 50 lb N/acre in February to mixtures increased total yields about 1990 lb/acre as compared with 0 N but had little consistent effect on alfalfa content of the sward and no effect on stand persistence. RecommendationAlfagraze alfalfa can be grown with endophyte-free tall fescue if adequately fertilized and cut at 4- to 6-wk intervals. The relatively good alfalfa persistence when cut at 3-wk intervals indicates that the mixtures can be rotationally stocked with cattle using a 3-wk rest period between grazings although alfalfa yield will be less than rotation with longer rest intervals. Applied QuestionDid Alfagraze alfalfa stands persist and remain productive in mixtures with AU Triumph tall fescue? Alfalfa maintained excellent stands in tall fescue when harvested at 6-wk intervals but declined when cut at 4- or 3-wk intervals (Table 2). Cutting at 3- or 4-wk intervals also decreased the percentage of alfalfa in the sward. When cut at 6-wk intervals, alfalfa constituted over 90% of the mixture during the third year. In contrast, alfalfa in the mixture cut every 3 wk declined from 50% the first year to 33% the third year. Alfalfa alone or in mixture supplied a greater percentage of total production during summer than did tall fescue alone. Tall fescue-alfalfa and alfalfa alone had yields which were superior to, or similar to, tall fescue fertilized with 150 lb N/acre. Table 1Nitrogen fertilization of tall fescue and mixtures. SpeciesNlb/acreAlfalfa alone0Fescue-alfalfa0Fescue-alfalfa50 in FebruaryFescue alone0Fescue alone50 in September, February, April Table 2Stand persistence and Alfagraze alfalfa composition of forage in mixtures with tall fescue when harvested at 3-, 4-, and 6-wk intervals, third year, Athens. AlfalfaAlfalfa-fescue + 50 lb N/acreAlfalfa-fescue 0 NShoots/square foot 3 wk cut 321512 4 wk cut 292011 6 wk cut 453330Percentage alfalfa in forage 3 wk cut1002233 4 wk cut1005537 6 wk cut1007292