The stocking rate (head of cattle per unit area or animals per
hectare) is perhaps the single most important factor in grazing
management. It will influence the persistence of pastures and
animal productivity and performance. Determining the appropriate
stocking rate for a given area can be difficult. In particular,
climatic variability makes it difficult to forecast the capacity of
an area to carry a certain head of cattle.The more variable the
rainfall, the more fluctuation in the optimum stocking rate. For
much of the tropical savannas, quality rather than quantity of
dry-season feed is the major limiting factor.
Cattle grazing on native pastures in the
Photo: NT DPIF
Lower stocking rates can be more sustainable as animals and
pastures can maintain condition and burning is more effective. If
the stocking rate is too heavy, pasture species composition
declines, weeds invade, soil is exposed to erosion and the country
is unable to carry hot fires. Animal health and condition is poorer
and their vulnerability to drought increases.
Stocking rates also vary significantly within the very large
paddocks that exist on properties in northern Australia. Cattle
tend to heavily graze areas where the pasture composition is best.
This results in a change in the composition of pasture species over
time, and less desirable species eventually dominate. There are
also other concerns relating to localised heavy grazing such as
soil erosion and weed invasion. While there are several ways of
addressing the tendency for cattle to graze unevenly over an area,
it remains one of the major management concerns for graziers in the
Adjusting total stock numbers is one way, but often this is not
financially viable. Opportunistic spelling, in which stock numbers
within a paddock are drastically reduced, is one approach that
allows pastures and land condition to fully recover. However, this
is only a viable option in very good years when there is plenty of
The distribution of watering points also influences where cattle
graze within an area as pasture condition tends to deteriorate with
proximity to water. So effective stocking rates can be reduced by
placing new watering points in distant regions, thus encouraging a
more even distribution of stock (Partridge 1999: 15).
Fencing is another, albeit expensive, means of controlling
cattle numbers and distribution. Stock access to "sweet" country
such as river frontages or areas with exceptionally good pasture
can therefore be controlled, and degradation of these more valuable
Finally, fire can be used to entice herds to graze more evenly,
as cattle graze indiscriminately over the 'green pick' of recently
burnt areas. Pasture condition is thus improved because preferred
pasture species are not overgrazed. It is important that recently
burnt pasture be left free of grazing until the grasses have
reached a height of around 15cm; heavy grazing immediately after a
fire can result in a decline of desirable pasture species, and can
expose the soil to erosion.
Pasture condition refers to the species composition of a pasture
community and the condition of the plants themselves. The most
valuable grasses for grazing are perennials, plants whose life
spans are longer than one growing season. Valuable perennial
grasses for cattle grazing include Mitchell grass (Astrebla
sp.) which copes well with relatively high stocking rates and
maintains its nutrient value over the dry season, bluegrass and
ribbon grass/ golden beard grass (Chrysopogon fallax).
Annuals such as Flinders grass (Iseilema sp.) can provide
some valuable feed at certain times throughout the year, however
they are much less resilient under heavy grazing than perennials.
(Partridge 1999: 8) Which is not to say that perrenials are
indestructible. With continuous and heavy grazing, the tops and
roots of these grasses become smaller and generally less
productive, and they will eventually be killed, allowing less
desirable species and weeds to invade. Animal production as a
result will decline.
The majority of grass growth in the tropical savannas occurs
during the first month or two of the wet season. Cattle gain most
of their weight at this point in the year, as their feed intake is
at its highest. However the large amount of pasture grass available
does not necessarily translate into nutritious feed. In fact the
While early wet season pastures are fairly nutritious, available
soil nutrients to be taken up are quickly diluted into the mass of
plant growth. The result, which occurs by about mid-February, is a
"green desert" in which there is a good deal of plant bulk but poor
quality herbage. Phosphorous is especially important at this time
as cattle are gaining weight.
Supplementary feeding is one way in which producers redress this
problem, allowing cattle to increase their intake of plant bulk by
up to 40 per cent (Partridge 1999: 35). The other is pasture
improvement, in which legumes such as Caribbean stylos (Verano and
Amiga), shrubby stylos (Seca and Siran) and Wynn cassia are sown.
Higher levels of protein and nitrogen, and better digestibility of
the leaves of these plants enable the cattle to gain more weight.
There are some risks associated with this approach, in particular a
loss of desirable native pasture species which may occur because of
the higher stocking rates.
Other introduced pasture species such as gamba grass and buffel
grass can greatly improve productivity. Many of these species
however can invade local ecosystems and out compete native grasses,
so they need to be carefully managed and controlled.
The amount of grass growth at the end of the wet season, as well
as species composition, should be used as an indicator for the
carrying capacity of an area over the dry season, since it is
unlikely that any new growth will occur. Producers should consider
as a bonus any winter rains, since these are very unreliable. If
there is a lack of palatable species or a problem with weeds, the
grazier may also factor in fuel levels required to carry a fire at
the end of the dry season, and limit stock levels accordingly to
allow fuel to accumulate.
Fire is an extremely important management tool in the tropical
savannas, and is second only to stocking rate management in its
capacity for maintaining healthy pastures. Compared to other
options it is also relatively cheap and easy to apply on a large
scale. The judicious use of fire can be beneficial in several
different respects. It can even out the impacts of preferential
grazing and encourage stock to move into underutilised areas. It
also can be instrumental in pasture species composition and
nutrient quality of feed.
One of the most significant applications of fire is in the
control of weeds and woody plants. A decrease in the use of fire
across much of northern Australia has seen a "thickening up" of
country under the latter. These woody trees can outcompete pasture
grasses for light and moisture, decrease the carrying capacity of
country and make mustering extremely difficult. The most effective
burns for the removal of these trees are hot, late dry-season
fires, although these are also the most dangerous and difficult to
control. Producers are then advised to burn firebreaks around the
targeted area early in the dry to ensure that fires later in the
season can be controlled.
The absence of fire in many parts of the savannas has also been
blamed for the incursion of exotic shrubs such as rubbervine,
mesquite, chinee apple and prickly acacia. These exotic weeds cause
similar problems to their native counterparts, effectively
decreasing the productivity of country. The other way that graziers
use fire is to mitigate against late dry season wildfires which can
be extremely destructive. Burning carried out earlier in the dry is
much safer, and reduces fuel available for later fires.
Overall there is still a lot to be learnt about the interaction
of fire and grazing, and the impact of both of these on broader
ecology. While it is generally accepted that fire is of benefit,
questions remain about optimum frequency and timing of fires to
achieve certain ends.
Wambiana: the big picture on grazing
Article about an 8-year research project at Wambiana cattle station near Charters Towers looking at different stocking strategies to deliver the best outcomes