Survivor populations of S23 perennial ryegrass from zero‐grazed and set‐stocked swards

Abstract

AbstractPerennial ryegrass tillers were collected from intensively used set‐stocked and zero‐grazed leys and from an old permanent pasture, grown on and compared at 30 cm spacing. All swards except the permanent pasture had been sown with cv. S23 and were of known age, ranging from 6 months to 11 years from sowing.Each genotype was scored for date of inflorescence emergence, and subsequently in vitro dry matter digestibility (DMD), D‐value of green leaf and the ratio of leaf dry weight: stem dry weight were determined.Both DMD and D‐value declined significantly in green leaf samples of populations from the older zero‐grazed swards but no significant changes were detected in populations from set‐stocked swards. In set‐stocked populations there was a shift towards later flowering.In zero‐grazed populations there was a consistent increase in the amount of leaf relative to stem with the age of the sward from which the plants were sampled. The survivor plants were more prostrate and leafier and it is suggested that under zero grazing, where cutting was to a uniform height, plants of this form were less severely defoliated and thus at a selective advantage.