Effect of early spring grazing frequency on the reproductive growth and development of a perennial ryegrass tiller population

Abstract

A population (1188) of vegetative perennial ryegrass tillers was identified at random in nine paddocks of an existing farmlet experiment. Groups of three paddocks (396 of identified tillers) were grazed every 8, 16, and 32 days from mid August until early November 1984, after which all paddocks were grazed every 32 days until the end of the experiment in May 1985. The physiological status (vegetative or reproductive) of live marked tillers and their orientation in the sward were determined at 7–12-day intervals during the experiment. Paddock botanical composition and tiller density were recorded in October, December, February, and May. Fifty percent of marked tillers became reproductive during the experiment. Reproductive development was concentrated in late October/early November. Different spring grazing frequencies did not affect reproductive development but frequent grazing resulted in tillers that were more prostrate than when grazing was less frequent. Reproductive tillers had a higher overall probability (P = 0.24 per week) of dying than did vegetative tillers (P = 0.09 per week), regardless of grazing treatment. Defoliation during summer/autumn significantly increased the probability of vegetative tiller death. A fast spring rotation increased ryegrass and Poa tiller densities in October after which the effects disappeared.

Keywords:

• spring grazing rotation
• reproductive development
• Lolium perenne
• seasonal effects
• tiller deaths
• tiller losses
• tiller orientation
• dairy cattle grazing
• perennial ryegrass