REGROWTH OF SMOOTH BROMEGRASS (BROMUS-INERMIS LEYSS) FOLLOWING DEFOLIATION

Regrowth and production of tillers in smooth bromegrass (Bromus inermi s Leyss.) following defoliation to a 5-cm stubble height were monitore d throughout the summer and in early spring the following year in cent ral Saskatchewan. After defoliation, while smooth bromegrass was veget ative, forage began accumulating in 45-75 growing degree-days (GDD) wh en moisture was favorable. Regrowth ranged from 34 to 84 g m(-2). Plan ts also produced less than or equal to 51 g m(-2) of regrowth when def oliated at or before culm elongation in a year with above-average prec ipitation. In two dry years, regrowth was minimal and plants did not r egrow after defoliation in the later vegetative growth stages; however , new leaves were produced within 110-140 GDD. Following defoliation a t early vegetative growth stages, 1030-1180 GDD were needed to reach m aximum regrowth Total annual. production was either unaffected or redu ced 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 (871-9 51 m(-2)) was not significantly different among treatments. Regrowth f ollowing defoliation cannot be related to a particular growth stage, b ut rather it depends on growing conditions. If smooth bromegrass is de foliated once and rested until the next year, it should be recovered b y early spring and its productivity should be unaffected.