Performance of temperate perennial pastures in the Australian subtropics - 1. Yield, persistence and pasture quality

Irrigated, pure stands of perennial ryegrass (Lolium perenne cv. Yatsyn), prairie grass (Bromus willdenodii cv. Matua) and tall fescue (Festuca arundinacea cv. AU Triumph) were compared with Italian ryegrass (L. multiflorum cv. Concord) under grazing in the subtropics of south-east Queensland. Pastures were fertilised with 50 kg nitrogen/ha.month as urea and annual dressings of 20 kg phosphorus/ha and 50 kg potassium/ha (as superphosphate and muriate of potash, respectively). There were 4 pasture treatments grazed by multiparous Holstein-Friesian cows at 3 cows/ha in a 1-week-on, 3-weeks-off rotation with 2 replicates and 3 cows/treatment block. Feed on offer was measured weekly and pasture quality, at the mid point of each of the 4 seasons. Detailed measurements on plant and tiller dynamics were recorded on fixed quadrats within the grazing areas from November to May in the second and third years. Yield of pasture on offer was greatest with prairie grass and the difference was most marked in spring and early summer. Yield of fescue was generally higher than that from the other 3 grasses in the autumn. In the second and third summers, the grass weed component in the 2 ryegrass, and to a lesser extent the prairie grass, pastures was greater than the sown grass component. Fescue generally produced forage lower in quality than the other 3 grasses although the differences were small in summer. The forage quality of Italian ryegrass was higher than perennial ryegrass in most seasons and for most attributes measured. Generally prairie grass had similar quality forage to the ryegrasses but at times it was as low as fescue. Fescue was the most persistent grass; it maintained a frequency of occurrence of 88, 56 and 71% in the first, second and third autumn periods, respectively, compared with 36, 37 and 21% for perennial ryegrass. To achieve these persistence figures, perennial ryegrass needed over-sowing in each autumn. Plant density and tiller numbers per plant fell in all grasses from November to May but the fall was significantly less in fescue than in other grasses. It was concluded that all 3 temperate perennial grasses demonstrated traits which were useful for subtropical dairy pastures. Fescue was the most persistent and the only grass which could sustain grazing in autumn. The performance of Italian ryegrass was as good as that of perennial ryegrass in the first year but fell substantially in the second and third years as the level of summer grass invasion suppressed the existing population and made oversewing increasingly less effective. Prairie grass produced the highest dry matter on offer under grazing, its forage quality was generally similar to that of the ryegrasses and it regenerated from self-sown seed.