Quantifying different causes of leaf and tiller death in grazed perennial ryegrass swards

Abstract

Death of plant material in grazed perennial swards results from a number of processes, particularly leaf senescence, tiller death, and grazing. These processes must be understood in detail to manage supply of high quality pasture for, especially, dairy cattle through the reproductive season. Although measurements have been made under a variety of pasture conditions, a generalised model has not yet been established. This paper reviews experimental evidence for the rates of leaf and tiller death resulting from five independent physical and physiological mechanisms operating in a grazed ryegrass‐dominant pasture. First‐order (linear) models are formulated to predict the rates of leaf and stem death on vegetative and reproductive tillers in such a pasture. Leaf death rate accounts for 90% of dead matter production in the non‐reproductive season, and was found to be linearly correlated to soil temperature. During reproduction, decapitation of reproductive stems, usually prior to ear emergence, is the dominant source of dead material. These models provide an essential component of the detailed modelling of grazed pasture tissue dynamics.