Poor persistence of perennial pastures, particularly perennial ryegrass (Lolium perenne)-based pasture, is a major problem for the dairy industry in southern Australia. The effects of pasture species mixture, management and environment on plant population density and persistence were studied in a field experiment at 2 sites for 4 years (1998–2001). Five pasture types, combined with 3 management treatments, were established on a light-textured soil at Naringal, and on a heavier-textured soil at Terang in south-west Victoria in April 1998. The 5 pasture types were: (1) Old persistent type; (2) District mix; (3) Stoloniferous clover; (4) Alternative grasses; and (5) High producing. Most of the types were ryegrass-based except for Alternative grasses that consisted of tall fescue (Festuca arundinacea), cocksfoot (Dactylis glomerata L.), and phalaris (Phalaris aquatica L.). The 3 management treatments involved different levels of fertiliser input and weed/pest control.

There were significant differences in sown grass tiller density between pasture types in all years. Tiller density of the Alternative grasses remained at around the same level (95–105%) as its establishment tiller density, compared with only 55–62% for ryegrass-based pastures 3–4 years after sowing. Inclusion of stoloniferous white clover cvv. Prestige and Sustain significantly increased sown legume density in 3 out of 4 years. However, the overall legume density was low across all treatments. There was a significant negative exponential relationship between density of sown and volunteer species (predominantly annual grasses and broadleaf weeds). Soil fertility did not affect pasture persistence due to a high basal fertility level at both sites. Pasture persistence was poorer on the light-textured soil than on the heavier soil where soil moisture stress was a major limiting factor. Higher endophyte incidence in perennial ryegrass pasture appeared to improve its persistence. The results suggest that the sown species density should be maintained at >3000 growing points/m² for ryegrass-based pasture types and >2300 growing points/m² for Alternative grasses, to achieve a pasture composition with over 70% of sown species.