A grazing study was conducted, over a 3-year period (1997–99), on the
subtropical north coast of New South Wales, Australia, to compare the yield of
prairie grass (Bromus willdenowii cv. Matua), tall
fescue (Festuca arundinacea cv. Vulcan) and perennial
ryegrass (Lolium perenne cv. Yatsyn), on a well-drained
red krasnozem soil at Wollongbar Agricultural Research Institute (WAI) and on
a heavy clay soil at Casino. The effect of grazing interval (equivalent to the
time taken to regrow 1.5, 2.5 or 4 leaves/tiller) in spring, and forage
quality of prairie grass in winter and spring was also assessed. At both
sites, the dry matter (DM) yields of prairie grass over the establishment year
and in year 2 were significantly (P<0.001) higher
than for the other 2 grass species (mean for 2 years over the 2 sites was
23.8, 8.9 and 7.7 t DM/ha for prairie grass, ryegrass and tall fescue,
respectively). In year 3, there was no production of tall fescue or ryegrass
at the WAI site while prairie grass produced 11.3 t DM/ha although this
was obtained from natural seedling recruitment after the sward was sprayed
with a herbicide in February of that year. At the Casino site, ryegrass and
tall fescue still made substantial growth in year 3 (3.1 and 2.1 t DM/ha
for ryegrass and tall fescue, respectively) but this was significantly below
the yields of prairie grass (5.5 t DM/ha). More frequent grazing of
prairie grass in spring (equivalent to 1.5 leaves/tiller of regrowth) led
to significantly (P<0.05) less plants surviving
summer and less seedling recruitment in the following autumn. The annual yield
of the 1.5 leaf treatment was significantly (P<0.05)
lower than the remaining treatments but only in the third year of the study.
Analysis of prairie grass forage samples, taken in June (vegetative sward) and
November (reproductive sward), gave magnesium values of less than 0.2%
DM which is below the concentration found in ryegrass and that recommended for
dairy cattle. The Ca : P and K : (Ca + Mg) ratios in prairie grass
improved, as a forage for dairy cows, with regrowth time up to 5
leaves/tiller. Metabolisable energy remained constant with regrowth time
in June at 10.8 MJ/kg DM but fell significantly in November from 10.7
MJ/kg DM, immediately post-grazing, to 9.2 MJ/kg DM at the 4.5
leaves/tiller stage of regrowth.
In contrast to observations in ryegrass, the water-soluble carbohydrate
content of forage samples of prairie grass taken in November showed a
substantial increase with regrowth time to over 12% DM at the 3
leaves/tiller stage of regrowth.
The high productivity and forage quality of prairie grass obtained over a
3-year period suggests this grass species could be a suitable temperate
perennial grass for subtropical dairy pastures. An appropriately long grazing
interval in spring seems critical to optimise plant survival over summer and
for adequate seed set for seedling recruitment the following autumn. If summer
weeds and/or grasses invade to a significant extent, the large seedbank of
prairie grass provides the opportunity to spray out the pasture in summer and
rely on seedling recruitment to establish a new sward in autumn. The forage
quality of prairie grass in winter and spring is similar to perennial ryegrass
but the magnesium levels are substantially lower and stock grazing this type
of pasture for extended periods would need to be supplemented with this
mineral.
