Supplementary feeding
The very high wet-season rainfall greatly affects the grazing
management regime in the Darwin-Kakadu region. Much of the area
suffers from very limited available soil nutrients, especially
nitrogen and phosphorus. Phosphorus is particularly a problem in
coastal areas, except for black soil floodplains which have
adequate levels.
The first two to three months of the wet season are vital as
this is the only time stock have access to relatively high-quality
feed. This time of year is their sole opportunity to grow and to
build up condition. However, by the end of the wet season the
digestibility of native pasture feed is very low, making it
difficult to get adequate energy for continued growth.
Phosphorus supplementation is only efficient during the wet
season, when stock are actively growing. At this time it is stored
in the bone and then drawn on in periods of poor nutrition from
body reserves. Sodium and sulphur are generally added to licks at
this time as well.
As protein levels in dry feed are below maintenance levels,
nitrogen levels in the supplement are increased from the late dry
season throughout the dry. This allows the herd to consume more
pasture dry matter. There are also mineral elements, salt and so
forth that may need to be added to licks at various times but these
tend to fluctuate locally.
Green feed tends to have sufficient levels of protein for
ruminants. This is why some producers in the Top End carry out
patch burning during the first month or two of the dry. At this
time there is still enough soil moisture to allow some 'green pick'
regrowth. This allows producers to put off protein supplementary
feeding until a little later in the dry season. Grazing pressure at
this point must be carefully managed to ensure that grasses are not
grazed too soon after burning, or grazed too heavily.
An alternative is using improved legume pastures saved from over
the wet season for dry season grazing. This practice requires input
of phosphorus based fertiliser but reduces the need for feeding
supplements.
Fencing
Maintaining fences can pose a challenge to producers with
significant areas of floodplain country. For some it is preferable
to take down the fences on the floodplains every year, rather than
have to mend them and clear them of the debris left behind by the
floodwaters. Alternatives include floating, flood-cleansing and
electric fences. However, the labour intensive nature of managing
these tracts for grazing is compensated for by the fact that these
areas provide such rich grazing country once the waters drain
away.
Outside of floodplain areas, this region has quite good fencing
rates, although some of the larger properties are still not
adequately fenced.
Burning
Fire is used by the majority of pastoralists in the region, with
a first priority to reduce the risk of damaging late dry season
fires. The very high rainfall in this region means that fuel levels
in areas which are not grazed may build up to high levels by the
dry season, increasing the potential for late dry season wildfires.
Patch burning is one management practice which mitigates against
the severity and incidence of these fires. Increasing numbers are
now using fire for the additional benefits of reducing rank
pasture, and for grazing management. That is, to encourage cattle
to graze areas of differing palatability more evenly. (see Ban Ban
Springs page)
Introduced pastures
Current markets for cattle and buffalo from the Top End require
animals to reach a targeted weight range at a certain age. To reach
these targets, they must grow more quickly than is possible by
grazing native pastures alone. In the farming systems being adopted
in the Darwin-Kakadu region, alternative feed sources are the use
of crop stubbles, ley pastures or long-term sown pastures.
Stylo, a legume, is the major improved pasture in the south of
the region around Katherine. Closer to Darwin, native pastures
mature rapidly and so better production is achieved using more
intensive systems. Improved grass pastures have the potential to
push up cattle production in live weight gain by 200 to 300 per
cent per year, and increase carrying capacity from one head per 15
- 40 hectares, to one for every one to two hectares. Costs of
setting up this kind of intensive system are high however, as much
as $350 per hectare. Ongoing maintenance costs are also high.
Common grasses used in the Katherine-Daly region include sabi
grass (Urochloa mosambicensis), buffel grass (Cenchrus
ciliaris), and finger grasses (Digitaria spp.) with
legumes such as Caribbean stylo (Stylosanthes hamata) and
round leaf cassia (Chamaecrista rotundifolia). On the
coastal uplands, pangola grass (Digitaria eriantha), Tully
(Brachiaria humidicola) gamba grass (Andropogon
gayanus), and of late, finger grasses have been sown.
Para (Brachiaria mutica), hymenachne (Hymenachne
ampexicaulis) and aleman grass (Echinochloa polystachya)
are used on floodplain areas.
Some introduced pasture plants can also become weeds in
non-grazing environments. They may outcompete other native plants
or contribute greatly to the fire fuel load. Great care needs to be
taken to ensure that the seeds of these grasses are not spread via
vehicles, machinery or hay.
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Millions of dollars have been spent on the
control of Mimosa in the Darwin/ Kakadu region
Photo: Martin Armstrong PWCNT
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Weeds
A major weed problem for this tropical savanna region is giant
sensitive plant (Mimosa pigra) which inhabits floodplain
areas. This plant has a current distribution of around 80 000
hectares, and can be found from the Moyle River in the west to the
Arafura Swamp in Arnhem Land. The seed is mainly spread by
floodwaters, and it establishes dense prickly thickets along
watercourses and on floodplains. In this way it affects stock
access to waters and pastures, and can hinder mustering.
Other major weeds are broad leafed plants which are not
palatable to cattle and shade out native pastures. These include
several varieties of Sida sp. (Sida acuta, Sida
cordifolia and Sida rhombifolia), hyptis (Hyptis
suaveolens), and sicklepod (Senna obtusifolia). These
weeds have decreased the productivity of significant areas of
pastoral land.
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Head of gamba grass. Care must be taken not to
spread these grasses beyond property boundaries
Photo: Martin Armstrong, PWCNT
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Grass weeds of the region include pennisetum (Pennisetum
pedicellatum) around the Katherine/ Daly region, gamba
(Andropogon gayanus) and mission (Pennisetum
polystachium) grass on the rural fringes of Darwin and olive
hymenachne (Hymenachne amplexicaulis ) in the Mary River
National Park.
Feral animals
The major feral animal pest in the Top End is the pig. These
animals cause considerable disturbance to the ground as they hunt
for edible roots and invertebrates in the soil. This destructive
'rooting' behaviour tends to occur when the soil surface is damp,
which coincides with the optimum germination window for many native
flora species. The end result is that native plant communities
around rivers and floodplains with pig infestations may not
regenerate as normal. The disturbed environments however are ideal
for the establishment of many weeds such as Mimosa pigra
.
In recent years however, the development of an export market in
wild boar meat has meant that land owners have been profiting from
the hunting and sale of feral pigs, which has tended to keep the
populations under some control. These animals nevertheless continue
to cause an enormous amount of damage to waterways and
floodplains.
