Growth and senescence of the successive leaves on a cocksfoot tiller. Effect of nitrogen and cutting regime

The effects of nitrogen supply and cutting regime on the morphological characteristics (leaf appearance and expansion rates, leaf growth duration, leaf lifespan) of a cocksfoot sward were studied over three growing seasons to gain a better understanding of the changes in tiller characteristics (length and age of laminae, number of leaves per tiller) over time and in different seasons. We show that, for a given regrowth, the lamina expansion rate at the tiller level depended on herbage nitrogen status, but the time course of its components differed according to nitrogen supply. When nitrogen was supplied, leaf appearance was faster but also decreased faster. In other words, the length of successive laminae increased faster when nitrogen was supplied. The same was true for the growth duration of the laminae and their lifespan. These changes resulted from the length of the sheaths from which the successive laminae emerged. As nitrogen increased cell number, it changed the ratio of lamina length(n+1)/sheath length, more than the ratio lamina length(n)/sheath length, at the same insertion level. Therefore sheath length increased faster and leaf appearance decreased faster when nitrogen was supplied. This finding helps to explain the effects of different heights and frequencies of cutting in terms of their effects on sheath length. (C) 2000 Annals of Botany Company.