Competitive interaction of grasses with contrasting temperature responses and water stress tolerances

Abstract

Lolium perenne (cv. Kangaroo Valley ryegrass), L. perenne x multiforum (cv. 'Grasslands Manawa' short rotation ryegrass), Phalaris tuberosa (cv. Australian Commercial),Festuca arundinacea (cv. Demeter) and Paspalum dilatatum were grown for 2 years in monoculture and two-species mixtures, under dryland and irrigated treatments at Armidale, N.S.W. Competition effects were described, with the use of diallel analysis. Early aggressivities were in the order L. perenne × multiflorum > L. perenne > F. arundinacea = P. tuberosa > P. dilatatum in both water treatments; subsequently, the aggressiveness of F. arundinacea, P. tuberosa and P. dilatatum increased relative to the ryegrasses (especially L. perenne), P. tuberosa (more so in the dryland treatment) and P. dilatatum (particularly in summer and autumn). Specifically high aggressivities of P. tuberosa towards P. dilatatum and P. dilatatum towards L. perenne were shown. Under dryland conditions, the P. tuberosa monoculture produced the highest yield in both years, differing markedly from L. perenne × multiforum in response to limited water availability. Under irrigation overall gains of yield were obtained by mixing grasses in the second year, the gains being significant for ryegrass-P. dilatatum mixtures. This response is related to the different growth potentials of the species in different seasons with the proviso that conditions such as water stress or excess suppression do not limit the expression of these potentials. Although P. dilatatum was of lower digestibility than the ryegrass, the difference was not sufficiently large to cancel the gain from mixing when expressed as digestible organic matter (DOM). An unsatisfactory feature of these mixtures was the depressive effect on winter yield of dormant P. dilatatum. By comparison, winter yield stimulation by mixing P. tuberosa and L. perenne, occurring when digestibilities were high, contributed to a significant gain of DOM yield by this mixture. Marked dominance of L. perenne × multiforum under dryland conditions, although appearing to assist the survival of this species in mixture, was detrimental in that by suppressing P. tuberosa, F. arundinacea and P. dilatatum, it restricted the potential of these species to produce in dryland conditions. There was evidence that F. arundinacea depressed yield in mixture, especially when associated with L. perenne.