Tactical versus continuous stocking in perennial ryegrass-subterranean clover pastures grazed by sheep in south-western Victoria - 2. Ryegrass persistence and botanical composition

A 4-year field experiment was carried out in south-western Victoria to dete rmine whether tactical stocking might improve perennial ryegrass (Lolium pe renne L.) persistence and prime lamb production, compared with the more com mon practice of continuous stocking. Tactical stocking consisted of variabl e-length summer, autumn and winter rotations and continuous stocking in spr ing. The 2 grazing strategies were compared on 2 contrasting pastures: an u pgraded pasture, sown with newer cultivars of perennial ryegrass and subter ranean clover (Trifolium subterraneum L.) with 26 kg phosphorus/ha. year, a nd a more typical naturalised perennial ryegrass pasture receiving 6 kg pho sphorus/ha. year. Paddocks were grazed by Border Leicester x Merino ewes, w hich were mated to a terminal sire to lamb in September. The effects of the grazing systems and pasture treatments on ryegrass persistence and pasture botanical composition are presented in this paper. The perennial ryegrass component of the sward decreased from an average mas s of 1000 kg dry matter/ha on the upgraded pasture and 400 kg dry matter/ha on the typical pasture in spring 1996 to 100 kg dry matter/ha and <50 kg/h a for the 2 pasture types, respectively, in spring 1998. This occurred irre spective of the grazing system imposed. The decline of ryegrass was attribu ted to several factors including the very dry 3-year period, summer rainfal l events that caused ryegrass buds to break dormancy then die when dry cond itions resumed, the gravelly soil type where the experiment was located, an d the high grazing pressure used. A number of species became more prevalent in the pastures as the ryegrass d isappeared. Silver grass (Vulpia spp.) increased 4-5-fold on all treatments . By the fourth year, barley grass (Hordeum leporinum) and Bromus spp. had increased significantly with tactical stocking compared with continuous sto cking. Capeweed (Arctotheca calendula L.) and Erodium spp. increased on bot h the continuously stocked and upgraded pastures. The subterranean clover c omponent was maintained across all treatments over the 4 years, indicating that tactical stocking did not adversely affect clover persistence. Since r yegrass declined irrespective of treatment, the tactical stocking system us ed in this study cannot be recommended for improving ryegrass persistence.