A 4-year field experiment was carried out in south-western Victoria to
determine whether tactical stocking might improve perennial ryegrass
(Lolium perenne L.) persistence and prime lamb
production, compared with the more common practice of continuous stocking.
Tactical stocking consisted of variable-length summer, autumn and winter
rotations and continuous stocking in spring. The 2 grazing strategies were
compared on 2 contrasting pastures: an upgraded pasture, sown with newer
cultivars of perennial ryegrass and subterranean clover
(Trifolium subterraneum L.) with 26 kg
phosphorus/ha.year, and a more typical naturalised perennial ryegrass
pasture receiving 6 kg phosphorus/ha.year. Paddocks were grazed by Border
Leicester x Merino ewes, which 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 mass
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/ha for the 2 pasture types, respectively, in
spring 1998. This occurred irrespective of the grazing system imposed. The
decline of ryegrass was attributed to several factors including the very dry
3-year period, summer rainfall events that caused ryegrass buds to break
dormancy then die when dry conditions resumed, the gravelly soil type where
the experiment was located, and the high grazing pressure used.
A number of species became more prevalent in the pastures as the ryegrass
disappeared. 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 stocking.
Capeweed (Arctotheca calendula L.) and
Erodium spp. increased on both the continuously stocked
and upgraded pastures. The subterranean clover component was maintained across
all treatments over the 4 years, indicating that tactical stocking did not
adversely affect clover persistence. Since ryegrass declined irrespective of
treatment, the tactical stocking system used in this study cannot be
recommended for improving ryegrass persistence.