Sward management effects on forage component responses in a production system for early weaned calves
There has been limited research to define appropriate management practices for pastures grazed by early weaned calves. Experiments were conducted from January to April (cool season) and May to July (warm season) 2003 and 2004 to evaluate the effects of N fertilization and regrowth interval on herbage mass and nutritive value of rye (Secale cereale L.)-annual ryegrass (Lolium multiflorum Lam.) mixtures and ‘Tifton 85’ bermudagrass (Cynodon sp.). Treatments were the factorial combinations of three N fertilization rates (0, 40, and 80 kg ha–1 period–1, with two periods per season) and two regrowth intervals (3 and 6 wk for rye-ryegrass and 2 and 4 wk for bermudagrass). Rye-ryegrass herbage mass increased linearly from 0.9 to 1.8 Mg ha–1 period–1 as N fertilization increased. There was no effect of regrowth interval on rye-ryegrass herbage mass during the winter; but in the spring, herbage mass was greater for the 6-wk vs. the 3-wk interval (2.2 vs. 1.6 Mg ha–1). For bermudagrass, there was a linear increase in herbage mass (1.6 to 2.6 Mg ha–1 period–1) and in vitro digestible organic matter (IVDOM) (480 to 530 g kg–1) with increasing N fertilization. Regrowth interval effects on rye-ryegrass were more important in spring than winter in determining forage nutritive value and herbage mass; shorter regrowth intervals may be necessary in spring to maintain calf gains. During the warm season, shorter regrowth intervals for Tifton 85 resulted in forage with greater nutritive value, which is the key factor limiting growth of early weaned calves.