Replacement series studies of competition between tropical perennial and annual grasses and perennial grass mixtures in northern New South Wales

Seedlings of three perennial tropical grasses, Chloris gayana cv. Katambora (Rhodes grass), Panicum coloratum var. makarikariense cv. Bambatsi (panic grass), and Digitaria eriantha ssp. eriantha cv. Premier (digit grass), were each grown in replacement series mixtures with seedlings of the annual summer-growing grass weeds Urochloa panicoides (liverseed grass) and Echinochloa colona (awnless barnyard grass). A separate experiment examined the competitiveness of seedlings of the three perennial tropical grasses when two species were sown together. Plants were sown 50 mm apart in boxes at a density of 307 plants/m 2 . Maximum likelihood estimates were used to derive parameters of a non-linear competition model using the dry weights of perennial and annual grasses. Seedlings of the summer-growing annual liverseed grass competed aggressively with those of the tropical perennial Katambora Rhodes grass. However, Bambatsi panic seedlings were equally competitive with those of awnless barnyard grass, while those in a Premier digit-barnyard grass mixture were inhibited by the presence of each other. In the perennial grass mixtures study, the performance of both Premier digit and Bambatsi panic was adversely affected by the presence of Katambora Rhodes grass.