Tiller appearance and death of Lolium perenne in mixed swards grazed by dairy cattle at two stocking rates

Abstract

Ryegrass tiller appearance, death, and density were examined in perennial ryegrass — white clover pastures stocked with 2.77 (LSR) or 4.28 (HSR) dairy cows per hectare. Rates of tiller appearance and death were highest between November and January and were low and variable between February and October. Tillering in autumn was low and similar to that in winter (27.8 and 27.7 tillers/m² per day, respectively). The rate of tiller death (but not appearance) was influenced by stocking rate, and was greater (P<0.01) in LSR than HSR swards during spring (29.5 and 21.2 tillers/m² per day, respectively) and summer (61.3 and 39.9 tillers/m² per day, respectively). Higher tiller death rates in LSR swards resulted in lower (P<0.05) tiller density during summer and autumn and reduced heterogeneity of tiller age population. Herbage mass in autumn was composed of more (P<0.05) new tillers in LSR than HSR swards (61.1 and 46.4%, respectively). Herbage mass in winter and spring consisted of a variety of tiller age classes, whereas that in summer and autumn, particularly in LSR swards, was composed predominantly of new tillers and tillers from the previous season. The more severe grazing on HSR compared to LSR swards maintained sward density and increased tiller survival during spring and summer. The implications for grazing management are discussed.

Keywords:

• grassland management
• dairy cattle
• Lolium perenne
• grazing intensity
• perennial ryegrass
• white clover
• tiller appearance
• tiller death
• tiller dynamics