Regrowth of smooth bromegrass (Bromus inermis Leyss.) following defoliation

Regrowth and production of tillers in smooth bromegrass (Bromus inermis Leyss.) following defoliation to a 5-cm stubble height were monitored throughout the summer and in early spring the following year in central Saskatchewan. After defoliation, while smooth bromegrass was vegetative, forage began accumulating in 45–75 growingdegree-days (GDD) when moisture was favorable. Regrowth ranged from 34 to 84 g m−2. Plants also produced ≤ 51 g m−2 of regrowth when defoliated at or before culm elongation in a year with above-average precipitation. In two dry years, regrowth was minimal and plants did not regrow after defoliation in the later vegetative growth stages; however, new leaves were produced within 110–140 GDD. Following defoliation at early vegetative growth stages, 1030–1180 GDD were needed to reach maximum regrowth. Total annual production was either unaffected or reduced by defoliation. Total annual production ranged from 35 to 139 g m−2, with yields lowest when defoliated in early May or early June and highest when herbage was removed in mid-May or near flowering and seed production. When plants were defoliated during vegetative growth most tillers were produced the following spring, whereas when plants were defoliated during reproductive phases the majority of tillers emerged in the fall. The year after defoliation, the density of tillers (871–951 m−2) was not significantly different among treatments. Regrowth following defoliation cannot be related to a particular growth stage, but rather it depends on growing conditions. If smooth bromegrass is defoliated once and rested until the next year, it should be recovered by early spring and its productivity should be unaffected. Key words: Etiolated growth, forage production, grazing management, regrowth, rest requirement, tillering