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

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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 of ryegrass-paspalum mixtures in northern New Zealand and management objectives to obtain efficient light interception and tiller populations are discussed.

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