Tiller dynamics of perennial ryegrass cultivars derived from different New Zealand ecotypes: effects of cultivar, season, nitrogen fertiliser, and irrigation

Abstract

A field study was made of the tiller dynamics of the New Zealand perennial ryegrass (Lolium perenne L.) cultivars Grasslands Ruanui, selected from a Hawke's Bay ecotype, and Ellett, selected from the Mangere ecotype. The work tested whether nitrogen (N) fertiliser or irrigation (Irr) could manipulate the persistence strategies of these morphologically distinct perennial ryegrass ecotypes, represented by these cultivars. Tiller births and deaths, and tiller survival, were monitored over 2 years, under rotational grazing by dairy cows. Patterns of cultivar tiller birth and death were similar. Much of the temporal change in tiller population density was shown to be a response to increasing or decreasing herbage mass associated with seasonal feed surplus or deficit. The probability of tiller survival between observation dates varied markedly with date, and was lowest in autumn. The cultivar effect on tiller survival was small but a significant (P < 0.05) cultivar × date interaction was detected, with survival probability for Ellett tending to be higher than for Grasslands Ruanui in March–April 1997 but lower from July 1997 until March 1998. A cohort effect on tiller survival was also identified, in that tillers formed in January, July, and August 1997 had lower survival probability than those formed at other times. N-treated plots produced 34% more tillers than did untreated plots, and irrigation had no effect on overall tiller density. N and Irr treatments had variable effects on tiller survival. Size density compensation theory and analysis of survival probability are introduced to aid the interpretation of tiller dynamics data.

Tillering dynamics in massai grass fertilized with nitrogen and grazed by sheep

“…When the tillering stability index is below 1.0, indicates that the survival rate combined with the appearance rate of tillers was not enough to offset the mortality rate and the plant population in the pasture ecosystem tends to decrease. Instead, a stability index higher than 1.0 (Table 2) points an inverse situation, and value equal to 1.0 indicates a stable tiller population, where the number of tillers in the pasture hardly varies, despite being a result of a dynamic balance in the pasture (BAHMANI et al, 2003).…”

“…The similarity in the DTPD regardless of nitrogen levels, even with this nutrient influencing the TMR, can be attributed to the positive effect of nitrogen fertilization in the balance between rates of survival and appearance of tillers, i.e., in the tillering patterns of the grass, defining according to 452 Tillering dynamics in… LOPES, M. N. et al Hirata & Pakiding (2001) and Bahmani et al (2003), the stability of tiller population in the pasture.…”

“…This evaluation can be done through the stability index of tiller population (BAHMANI et al, 2003). When the tillering stability index is below 1.0, indicates that the survival rate combined with the appearance rate of tillers was not enough to offset the mortality rate and the plant population in the pasture ecosystem tends to decrease.…”

“…The tillering stability index (P1/P0) was calculated as recommended by Bahmani et al (2003), using the equation: P1/P0 = TSR (1+TAR), where TSR (tillers survival rate) = 1-TMR. It was also determined the population density of vegetative tillers (PDVT, tillers m -2 ), population density of dead tillers (PDDT, tillers m -2 ), population density of reproductive tillers (PDRT, tillers m -2 ), tiller biomass (TB, g tiller -1 ) and vegetative/dead tillers ratio (VT/DT).…”

Perfilhamento em pastagens de azevém em sucessão a soja ou milho, sob diferentes métodos e intensidades de pastejo

“…As taxas de aparecimento e de mortalidade de perfilhos foram integradas de forma a gerar diagramas sazonais de estabilidade do pasto, propostos para azevém perene (Lolium perenne L.) por Bahmani et al (2003). O índice de estabilidade do pasto (IEP) foi calculado pela equação: Pf/Pi = TSP (1 + TAP), em que: Pf/Pi = IEP, expresso como a proporção da população de perfilhos final (Pf) e inicial (Pi), em um determinado período de avaliação; TSP, taxa de sobrevivência de perfilhos; e TAP, taxa de aparecimento de perfilhos.…”