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EnviroNorth > Darwin-Kakadu > Grazing > Sustainable Grazing

Sustainable grazing

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.

Mimosa

Millions of dollars have been spent on the control of Mimosa in the Darwin/ Kakadu region
Photo: Martin Armstrong PWCNT

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.

Gamba grass

Head of gamba grass. Care must be taken not to spread these grasses beyond property boundaries
Photo: Martin Armstrong, PWCNT

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.