Seed Production Studies on Perennial Ryegrass, Timothy and Prairie Grass

Abstract

A study over two years involving tiller identification according to month of origin enabled the contribution of individual tillers of perennial ryegrass Grasslands Ruanui, timotby Grasslands Katbu and a local New Zealand strain of prairie grass (Bromus unioloides) to be deternnined at seed barvest. In addition, tbe distribution of seedbeads in different arbitrary emergence groups was detennined so as to allow analysis of individual seedhead components witbin each group.In all species, tillers formed during tbe first 4 months following an autumn sowing in tbe first year, and also in tbe immediate post-barvest period and tbrougb tbe autumn in tbe second year, made a major contribution to seedhead numbers and seed yield at harvest. These tillers bad a lower vegetative mortality rate than those formed in the spring.Primary tillers formed after sowing were highly persistent and became almost exclusively reproductive. Many vegetative tillers died before barvest, bebaving as annual tillers.Spring-formed tillers made a major contribution to tbe vegetative growtb of tbe plant over the summer and early autumn. These tillers generally died before the following winter. Tillers formed in winter and early spring by ryegrass and prairie grass sbowed a bigb mortality, particularly in tbe second year. In timotby, mortality was bighest amongst tillers formed in late spring. Tbe reduced contribution of spring-formed tillers to tbe seedbead population occurred as a result of fewer beads numerically compared with older tillers.In all species, most seedhead components varied according to time of ear emergence. Earlyemerged heads were generally longer, bore more spikelets and more florets per bead and bad a greater culm lengtb tban late-emerged beads.Tbe major trend in all species was a general depression in bead lengtb, spikelet and floret number and culm lengtb witb grazing. Tbese effects were in most cases partly or completely overcome by N application. Tbe major effect of applied N was to increase floret number per bead.

The physiology of tiller death in grasses. 2. Causes of tiller death in a grass sward

“…0007-0750/78/0900-0205 $02.00 ©1978 Blackwei! Scientific Publications consistently revealed a significant turnover in tiller populations (Langer et al, 1964;Matthews and Westlake, 1969;Hill and Watkin, 1975;Bernard, 1976) and a recurring pattern of high mortality which occurs during each period of active growth. In a seed crop of ryegrass up to 60% of the tillers produced may die prematurely (Spiertz and Ellen, 1972;Hebblethwaite, 1977) and yet the causes of tiller death are not clearly established.…”

Biomass Partitioning Following Defoliation of Annual and Perennial Mediterranean Grasses

“…Grazing reduces the allocation to reproductive structures by removing rudimentary inflorescences or reducing photosynthetic surfaces and, consequently, the ability to photosynthesize (Hill and Watkin 1975, Caldwell et al 1981, Butler and Briske 1988. On the other hand, grazing can increase the allocation to reproductive organs through its influence on tiller density and age-class distribution (Deregibus et al 1985, Butler and Briske 1988, Noy-Meir and Briske 1996.…”

Some consequences of imposing different continuousgrazing pressures in the spring on tiller demography and leaf growth

“…It would appear that the increased proportion of tillers in the older categories in the S treatment populations caused a shift towards earlier flowering. It has long been known that the oldest tillers within the tiller population of a grass sward contribute the largest proportion of flowering tiller (Langer & Lambert, 1959;Hill & Watkin, 1975). Hill & Watkin (1975) also demonstrated that management, in their case grazing v. no grazing, can cause a shift towards higher numbers of early-emerging flower heads, but this is the first study to demonstrate long-term effects of spring grazing management on flowering in the following year.…”

“…It has long been known that the oldest tillers within the tiller population of a grass sward contribute the largest proportion of flowering tiller (Langer & Lambert, 1959;Hill & Watkin, 1975). Hill & Watkin (1975) also demonstrated that management, in their case grazing v. no grazing, can cause a shift towards higher numbers of early-emerging flower heads, but this is the first study to demonstrate long-term effects of spring grazing management on flowering in the following year. The earlier flowering of the S treatment swards would also have resulted in an earlier decline in the digestibility of the crop as the inflorescences matured (Spedding & Diekmahns, 1972).…”