Quantifying regrowth characteristics of three bromegrass (Bromus) species in response to defoliation at different developmental stages

Bromegrasses (Bromus) are widely cultivated for pasture and hay in temperate areas of the world. The objective of the present study was to determine above-and below-ground biomass, tiller density, and leaf area index (LAI) of meadow bromegrass (Bromus riparius Rehm.), smooth bromegrass (Bromus inermis Leyss.) and hybrid bromegrass (B. riparius × B. inermis) after defoliation. The study was conducted in 2006 and 2007 in Saskatoon (52°07′N, 106°38′W), Canada. Plants were clipped to a 5 cm height at the vegetative and stem elongation stages of growth, and an undefoliated control was included. Regrowth was similar (521 g m−2) among the three species when defoliated at the vegetative stage, but meadow and hybrid bromegrass produced 49% and 36% greater regrowth than smooth bromegrass following defoliation at the stem elongation stage. Compared with undefoliated plants, below-ground biomass was reduced 38% following defoliation. Meadow and hybrid bromegrass produced similar (4863 g m−3) below-ground biomass after defoliation, which was 66% greater than smooth bromegrass (2923 g m−3). LAI of all three bromegrasses increased linearly with days of regrowth (r2 ≥ 0.88, P < 0.05), and LAI was greatest in meadow bromegrass (4.0, 3.3), intermediate in hybrid bromegrass (3.6, 2.7), and least in smooth bromegrass (3.1, 2.2) following defoliation at the vegetative and stem elongation stages, respectively. Tiller density was also greatest in meadow bromegrass (2107, 1320 tillers m−2), intermediate in hybrid bromegrass (1547, 840 tillers m−2) and least in smooth bromegrass (1093, 520 tillers m−2) following defoliation at the vegetative and stem elongation stages, respectively. In the undefoliated control, 15% fewer tillers of meadow bromegrass reached the reproductive stage compared with the other two bromegrasses. The rapid regrowth of meadow bromegrass appears to be associated with more tillers, more rapid LAI development, and maintenance of greater below-ground biomass following defoliation.