Competition among pasture plants

Abstract

Simulated swards forming a replacement series of the ryegrass cultivars ‘Grasslands Manawa’ and ‘Grasslands Ruanui’ consisting of two monocultures and three mixtures were cut during establishment to two heights and at two frequencies. The cutting frequencies were continued for a year after the first cut, after which all swards were cut uniformly until the experiment was concluded 2 years after sowing.

Yields, tiller numbers, and plant survival were recorded separately for the cultivars. These data were used to fit parameters to the two-species competition model of de Wit (1960).

Manawa was initially dominant in all cutting systems, and this dominance was greatest where cutting was infrequent. Initial lax cutting reduced the suppression of Ruanui. The suppression of Ruanui during establishment is largely attributed to shading by Manawa, and where hard cutting removed stubble, Ruanui tiller numbers were reduced and Ruanui plants died in the mixtures with Manawa. This effect hindered the transition to dominance of Ruanui in the summer and autumn after sowing.

The results indicate that mixing of the cultivars would be advantageous as a function of both herbage yield and quality under the frequent lax cutting system, because the cutting did not markedly suppress Ruanui initially, allowing Ruanui to contribute substantially to the yields of the mixtures in the post-reproductive period when yields of Manawa were low. With infrequent hard cutting the yield contribution of Ruanui in mixture during the post-reproductive period was small and, because Manawa was unable to utilise the space made available by the death of Ruanui plants, depressed yields from mixing were observed. It is concluded that no advantage is gained by mixing Ruanui and Manawa where the management system in the first year tends to maximise the yield of Manawa.