EFFECT OF DIFFERENT GRAZING PERIODS ON YIELD AND PERSISTENCE OF ALFALFA CULTIVARS FROM DIFFERENT FALL DORMANCY GROUPS
R. Rossanigo
EEA Marcos Juarez-INTA, Argentina
The ideal management for alfalfa must combine high dry matter production with high quality and good persistence. Several studies have demonstrated that this could be feasible under grazing conditions. However, the negative effect of continuos grazing over vigor and persistence of alfalfa plants is well documented. On the other hand, the effect of appropriate rotational grazing systems in increasing forage yield, beef production ha-1, and persistence, and in decreasing weed invasion, is also well known. The specific needs for dairy or beef operations may introduce changes in the appropriate number of paddocks to use, affecting the frequency and intensity of grazing in each system. Assuming an adequate stocking rate, the number of paddocks directly affects the length of the grazing period, the length of the resting period, and the productivity of the alfalfa pasture. All these three aspects may also be influenced by fall dormancy.
The objective of this study was to determine, in a rotational system, the effect of grazing frequency on yield and persistence of alfalfa cultivars belonging to four different fall dormancy (FD) groups. The experiment was conducted at INTA’s Marcos Juarez Exp. Stn., Cdba., Argentina during three growing seasons. The treatments were evaluated in a factorial experiment with a split-plot design. Four cultivars, belonging to FD classes 3, 5, 7 and 9, were used as main plots. Four grazing periods of 2, 6, 12 and 18 days were used as subplots. A uniform resting period of 36 days was used for all treatments. As a result, four rotational grazing systems having 19, 7, 4 and 3 paddocks, respectively, were developed. Forage yield was estimated by cutting and weighting 1-m2 subsamples within each treatment. In the same way, persistence was estimated by counting the number of empty spaces in several 1-m2 subsamples. It was concluded that: a) Grazing periods for nondormant cultivars (FD 7-9) must be no longer than 7 days; b) The more dormant cultivars (FD 3 to 5) can tolerate longer grazing periods (or fewer number of paddocks) than nondormant cultivars; and c) A resting period of 36 days was appropriate for all tested cultivars.