Temperature and cutting effects on the growth and competitive interaction of ryegrass and paspalum

Abstract

Monocultures and mixtures of perennial ryegrass ('Grasslands Nui') and paspalum (,Grasslands Raki') were grown at high (24°C day/18°C night) and low (14°C day/8°C night) temperatures either continuously for 24 weeks or transferred between temperatures at 12 weeks. Defoliation treatments applied were cutting at 2-and 4-weekly intervals and frequent cutting immediately after temperature changeover. The effects of these treatments on dry matter production, tiller number per plant, and light interception are reported. Averaged over both grasses and their mixtures, yields were highest under high temperature and infrequent cutting. There was marked species x temperature interaction. Paspalum yielded most at high temperature and ryegrass at low temperature. Ryegrass-paspalum mixtures outyielded the monocultures and mixtures provided more stable yields over the range of temperature conditions. Response of the grasses to temperature changed with time. Ryegrass initially grew more rapidly at high temperature, but after 12 weeks growth, had higher yields at low temperature. Paspalum growth was severely reduced when transferred from high to low temperature, and rapidly increased when transferred from low to high temperature. Canopy development and consequently light interception was restricted, especially for paspalum, by low temperatures and by frequent cutting. Ryegrass had fewer but larger tillers at high compared to low temperature, and it rapidly changed to the contrasting habit form after temperature transfer. Paspalum tillers were short, prostrate, and largely below cuttmg height at low temperature, but elongated rapidly above cutting height at high temperature. Frequent cutting increased the tiller number of paspalum and reduced the tiller number of ryegrass. Because mutual shading occurred amongst competing plants in a simulated sward situation, these results from controlled environment conditions are more closely applicable to the field situation than results obtained from isolated plants. Use ofryegrass-paspalum mixtures in northern New Zealand and management objectives to obtain efficient light interception and tiller populations are discussed.

Temperature and cutting effects on the growth and competitive interaction of ryegrass and paspalum

“…Ryegrass and paspalum competed both above and below ground in this study, but frequent applications of water and nutrients should have minimised competition below ground and probably competition was largely for light. Consequently, infrequent cutting, by allowing fuller development of the canopy and increasing light interception (Harris et al 1981), generally reinforced the patterns of competitive dominance and suppression developing from the different growth rates of the grasses under different temperature regimes.…”

“…This experiment has established a relationship between the direct responses of ryegrass and paspalum to temperature (Harris et al 1981) and their competitive ability under different temperature regimes (Figs 1-4). Ryegrass and paspalum competed both above and below ground in this study, but frequent applications of water and nutrients should have minimised competition below ground and probably competition was largely for light.…”

“…Experimental details are provided by Harris et al (1981). Herbage production and changes oftiller numbers were recorded separately for each grass over a 24-week period for the series offive ryegrass: paspalum ratios of 1:0, 0.75:0.25, 0.50:0.50, 0.25:0.75, and 0: 1, under four temperature and three cutting treatments.…”

“…The direct effect of these variables on the growth of ryegrass and paspalum have been described in a previous paper (Harris et al 1981).…”

Simulation by cutting of stocking rate and rotational and continuous management

“…Although Mitchell's (1955Mitchell's ( ,1956 work with individual tiller and plants of ryegrass, the dominant species in the pasture, indicated an optimal temperature for growth in the range 18-24°C, the optimal temperature for growth of ryegrass in a community is probably lower (McWilliam 1978;Harris et al 1981) but still higher than average winter temperatures (Fig. 3).…”