Lucerne, phalaris, and wallaby grass in short-term pasture phases in two eastern Australian wheatbelt environments. 2. Effect of perennial density and species on subterranean clover populations and the relative success of 3 clover cultivars of different maturity
B. S. Dear A D , G. A. Sandral A D , J. M. Virgona A B D , A. D. Swan A C , B. A. Orchard A D and P. S. Cocks DA E H Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga Agricultural Institute, PMB, Wagga Wagga, NSW 2650, Australia.
B Current address: Charles Sturt University, Barooma St, Wagga Wagga, NSW 2650, Australia.
C Current address: CSIRO Division of Plant Industry, Canberra, ACT 2601, Australia.
D Cooperative Research Centre for Plant-based Management of Dryland Salinity, Perth, WA 6009, Australia.
Australian Journal of Agricultural Research 58(2) 123-135 https://doi.org/10.1071/AR05324
Submitted: 14 September 2005 Accepted: 18 October 2006 Published: 22 February 2007
Abstract
The effect of the density of 3 perennial species, phalaris (Phalaris aquatica L.), wallaby grass (Austrodanthonia richardsonii Kunth), and lucerne (Medicago sativa L.), on seed set, regeneration, and the relative competitiveness of 3 cultivars of subterranean clover (Trifolium subterraneum L.) was examined in 2 environments in the south-eastern Australian wheatbelt.
Seed yields of subterranean clover were inversely related to perennial density at both sites over the first 2 years, the relationship varying with perennial species. Phalaris depressed the seed yield of clover more than lucerne and wallaby grass in the second and third year at equivalent densities. Clover seed yield was positively related to clover herbage yield in late spring at both sites, and inversely related to perennial herbage yield. Clover seed yield displayed an increasing linear relationship with the proportion of light reaching the clover understorey in spring, which in turn was inversely related to perennial density and perennial herbage yield.
Clover seedling regeneration in mixed swards in autumn was positively related to the size of the summer seed bank, but negatively related to perennial density. Clover seedling survival following a premature germination at Kamarah was inversely correlated to the density of phalaris and lucerne in the sward.
The relative competitiveness of the 3 subterranean clover cultivars varied between sites, with climatic conditions (rainfall and growing-season length) having a greater effect on the relative cultivar performance than companion perennial species or density. The later maturing subterranean clover cv. Goulburn became the dominant cultivar at the wetter site, constituting 72% of the seed bank, but declined to only 3–8% of the seed bank at the drier site. The proportion of the early flowering cultivar Dalkeith in the seed bank increased over time at the drier site and was highest (53%) in plots with the highest perennial density.
We concluded that although perennial pasture species will depress clover seed yield and subsequent regeneration, these effects could be minimised by reducing perennial densities and exploiting variations in competitiveness between perennial species as identified in this study. Sowing earlier maturing subterranean clover cultivars would only be an advantage in increasing clover content in low-rainfall environments. The findings suggest that clover seed reserves and regeneration could also be increased by using grazing management to reduce the level of shading of clover by perennials, a factor associated with reduced clover seed yield.
Additional keywords: perennials, seed set.
Acknowledgments
The work was undertaken with financial support from the Grains Research and Development Corporation, project CSP216. The authors thank Mr A. Lehmann, ‘Hillside’, Illabo, and Mr J. Semmler, ‘Hillview’, Kamarah, for providing land for the experiments. BSD was financially supported by a research fellowship from Australian Wool Innovation. The authors gratefully acknowledge the suggestions of the anonymous referees.
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