Making sense of the link between tiller density and pasture production.

摘要

An interpretation of tiller or shoot density data is presented, including the resolution of 2 independent, confounding effects, namely size/density compensation and the leaf area effect. The implications of size/density compensation (that at higherherbage mass individual tillers or shoots are larger but population density is correspondingly decreased) are presented and the leaf area effect, which represents the difference in sward leaf area for 2 tiller populations, are also detailed. The geneticand environmental determination of such leaf area differences and their expression through change in tiller size and/or tiller density as 'yield components' of leaf area, are described and the theoretical basis for distinguishing between size/density compensation and the leaf area effect (considering tiller or shoot density and herbage yield, respectively, as x and y co-ordinates in a size/density plot) is outlined. When such a plot is drawn on a logarithmic scale, points along a line of 11/2 slope showsize/density compensation with respect to each other. Movement of points to the right or left of the size/density compensation line is evidence of a leaf area effect. It is shown that when the size/density effects are removed from a data set in this way, rankings of experimental treatments for the leaf area effect can often be reversed compared with the ranking of uncorrected tiller density, and it is suggested that tiller density data corrected for size/density compensation in this way may be a usefulindicator of sward productivity. Below a certain threshold herbage mass at which tiller density begins to fall below the size/density compensation line, higher tiller densities associated with heavier defoliation pressure are insufficient to compensatefor associated loss of leaf area. It is suggested that swards maintained at lower tiller density and higher herbage mass would theoretically be more productive.