Tiller weight versus tiller number in a perennial ryegrass population: a productivity index

摘要

In defining agronomic indicators of sward status, tiller population density is often intuitively linked with sward vigour and presumed to be indicative of productivity potential.However, grass swards are subject to tiller size‐density compensation and exhibit considerable plasticity, with shoot size and density subject to genetic variation, and varying with factors such as change in grazing height or seasonal light influx.A productivity index ( PI) representing combinations of tiller size and density predicted to result in higher (or lower) sward leaf area index ( LAI) and DM productivity ( Matthew et al., 1995) has been shown to be useful when comparing genetically similar swards under differing managements, but it is known that the cultivar Grasslands Ruanui has an anomalously high PI when compared with Grasslands Ellett (Bahmani et al.,1997).Here we report further investigation into factors affecting PI.