Competition among seedlings of perennial grasses, subterranean clover, white clover, and annual ryegrass in replacement series mixtures

Seedlings of 3 perennial grasses, Danthonia linkii Kunth cv. Bunderra, D. r ichardsonii Cashmore cv. Taranna (wallaby grasses), and Phalaris aquatica L . cv. Sirosa, were each grown in replacement series mixtures with seedlings of Trifolium repens L. (white clover), Trifolium subterraneum L. var. brac hycalycinum (Katzn. et Morley) Zorahy & Heller cv. Clare (subterranean clov er), and Lolium rigidum L. (annual ryegrass). Plants were sown 5 cm apart i n boxes (45 by 29 by 20 cm) at a density of 307 plants/m(2). Maximum likeli hood estimates were used to derive parameters of a non-linear competition m odel using the dry matter weights of perennial grasses and competitors at 3 harvests, approximately 168, 216, and 271 days after sowing. Intra-plant c ompetition was examined in monocultures of each species, grown at plant spa cings of 2, 5, and 8 cm apart with plants harvested at the above times. Competition occurred in all perennial grass-competitor mixtures, except in those of each perennial grass with white clover and the phalaris-subterrane an clover mixture (Harvest 1) and those with D. richardsonii and phalaris g rown with white clover (Harvest 2). For D. richardsonii (Harvests 1 and 2) and D. linkii (Harvest 1 only) grown with white clover and the phalaris-sub terranean clover (Harvest 1), the two species in the mixture were not compe ting. In the phalaris-white clover mixture, each species was equally compet itive (Harvests 1 and 2). These differences in competition and aggressivene ss reflected differences in individual plant weights in monocultures where there was an effect (P < 0.05) of species on dry matter weight per box, but no significant effect of plant spacing. These data indicated that for successful establishment, D. richardsonii and D. linkii should not be sown in swards with either subterranean clover or white clover, or where populations of annual ryegrass seedlings are likely to be high. Phalaris was more compatible with both white clover and subterr anean clover, but aggressively competed with by annual ryegrass.