Frequently Asked Questions
- What level of land resource information has been collected over a particular parcel of land?
- What key land and vegetation issues are critical when managing soil landscapes in the Top End?
- What land management issues are critical when managing land in the Central Australia?
- How can land resource information assist in sustainable land management?
- How does the scale of a survey determine the level of detail?
- What scale and type of mapping is suitable for a particular property size?
View the land unit map cover of the NT. Use the legend to establish what level of information has been published over the land parcel of interest. The best available mapping in the NT is generally 1:25 000, followed by 1:50 000 and 1:100 000. The 1:25 000 mapping is useful for detailed planning, such as Darwin and its rural areas, whereas 1:50 000 is more appropriate at a regional scale such as catchment planning in the Mary and Daly River catchments. The 1:100 000 mapping is more applicable for extensively managed lands such as the large pastoral properties of the Victoria River District.
If no land unit mapping is available view the land system map cover of the NT. Although not as detailed as the land unit information it is more extensive. Land systems provide broad scale information useful for pastoral land management and identifying land requiring more intense survey. Land systems surveys cover most of the NT at four broad scales. 1:100 000 land system mapping has been prepared in the Darwin region but has largely been superseded by more detailed land unit information. The Southern Gulf, Roper River Catchment and Arnhem Land have been mapped at 1:250 000. Outside these areas, for example the Ord-Victoria Area, Adelaide-Alligator Rivers Region, Barkly Tableland and Lower Daly, and where land unit mapping is not available only extremely broad information such as the Atlas of Australian Soils is available.
Intense rainfall during the wet season means that bare soil on the minimal of slopes (>0.5%) is an erosion risk. This means most land to be disturbed will require erosion and sediment control measures. Land Management advice concerning erosion and sediment control can be sought from this department. Always remember that it is far more cost effective to prevent land degradation then to rehabilitate after the event.
Poorly drained land or seasonally waterlogged land is also a major land management issue in the Top End, posing problems for urban housing, rural living and horticulture. During wetter months these soils lack oxygen needed for crops, posing operational and health problems for septic systems as well as the obvious problems associated with access and building foundations. These areas also often have conservation values for birdlife and are vital for catchment health. As a result these areas are often excluded from subdivisions in Darwin’s Rural Area. If poorly drained land is not excluded from a subdivision then a proposed lot requires at least 1ha of well drained accessible land. This allows enough land for housing and associated infrastructure such as a shed, bore and septic, which under law need to be at least 100m apart.
Landscape features in Central Australia vary from salt lakes to mound springs, sand dunes, floodplains, mountain ranges and broad alluvial plains. Soil types vary as much in Central Australia as landscape features. Most of Central Australia is to dry for agricultural production. Average annual rainfall in ‘the centre’ is 274mm with most rain falling in summer in brief storms. There is an annual evaporation potential of 2500mm to 2800mm. Pastoralism is the most widespread land use but such a large land area, enormous distances and small population can make land management issues critical for conservation of the soil resources. Soils in Central Australia are derived from strongly weathered parent material, generally shallow, low in fertility, and are very fragile.
Some land management issues that are apparent in Central Australia include;
- Land degradation resulting from over-grazing by feral animals (horses, donkeys, rabbits, and camels)
- Alterations in hydrology due to human activities, primarily but not exclusively drawdown in the Great Artesian Basin due to numerous uncapped bores.
- Removal of the environments on which animals depend through clearing.
- Invasion by weeds constitute an acute and formidable problem for biological diversity.
- Uncontrolled fire is significant in some places.
The vast majority of Central Australian soils have limitation which affects productivity or predisposes the land to degradation. It appears that responsible land management practices and the control of feral animals and plants are the only practical means of conserving the soil resource. Natural regeneration of degraded land in arid climate zones does occur but this is over a long time period of 25-50 years. Preventing degradation of our natural resources is far cheaper than rehabilitation.
Land resource information enables a potential purchaser of a particular land parcel to identify its capability. The buyer may have a plan of what they want to achieve but unless the land capability is able to match this type of land use then land degradation may occur.
In terms of rural living and hobby farming in the Greater Darwin area it maybe that a purchaser wants to grow horticultural crops all year round but if a significant part of the block is seasonally waterlogged or inundated then it will be difficult to achieve. If land has already been purchased then land capability information can help the landholder to identify what uses match its capability so that the land is not degraded over time.
When purchasing farming land, for example in the Katherine/Douglas Daly Region it is vital that crop selection and pasture management matches land capability. Land capability information can assist in estimating returns for a given area based on its land capability class. Land resource information presented in the form of land capability classes (low, moderate and high) is available across the Katherine/Daly Region.
Horticulture is a growing industry in the Top End. Soils of the Top End are not consistently suitable for horticultural crops so land resource information with an emphasis on horticultural potential is essential when considering new plantations. It is important that natural drainage areas are not disturbed for ecosystem maintenance as well as steep slopes for prevention of erosion and sediment control.
Land system of broad scale mapping has been used for by pastoralist for years in the Territory. This information is often requested when a property is valued. It is worth noting that more detailed information is now available across most properties in the Victoria River District and an increasing number of properties in the Alice Springs and Plenty Pastoral Districts. It allows a potential buyer to examine the potential of the property in terms of carrying capacity and turnover. Land resource information often confirms what land holders and managers already know however, it does help to quantify carrying capacity information, revealing useful figures on areas of land types. Erosion risk maps are useful for planning roads and fence lines so as to avoid where possible, steep slopes, flooded areas and erodible and unstable soils.
1:2 000 000 - 1:250 000
Reconnaissance or exploratory land system surveys (1:2 000 000-1:250 000) such as those covering large tracts of the Territory give a broad understanding of the types of landscapes with a particular emphasis on general geomorphic, landform, soil and vegetation descriptions. These surveys identify land where further work could be undertaken. They are generally not applicable to small scale farm planning and development assessment.
1:100 000- 1:50 000
Low to medium intensity surveys such as those captured at a scale of 1:100 000 or 1:50 000 has been undertaken across pastoral properties and major catchments in the Top End such as the Daly River and Mary River Catchments. These surveys provide more detailed descriptions. They have been used in the Katherine/Daly River area to highlight soils with agricultural capabilities as well as highlighting sensitive ecosystems requiring protection. However, the level of detail is still not present for detailed small scale farm planning.
Moderately high intensity surveys (1:25 000) are generally the most detailed surveys undertaken in the Territory. These surveys have targeted the Greater Darwin area, Top End coastal plains, the Alice Spring district and rural townships and their surrounds. This information is primarily used for assessing development applications, especially subdivision applications for lot sizes down to 2ha. It is also used for assessing the suitability of soils for intensive use such as horticulture in the Greater Darwin area and the coastal plains. Probably the most utilised map product applied at this scale is seasonal soil waterlogging information. This information is vital for planning in Darwin’s rural area, from the suitability of soils for septic absorption in the wet season, all weather driveway access to the protection of drainage areas and wetlands.
Land system information has been used across extensive pastoral leases for property management for many years however, better information is becoming available across many pastoral leases, especially in the Victoria River District, Alice Springs, Plenty and Tennant Creek Pastoral Districts. Larger scale information (1:25 000) should always be used where available. The increased intensity of data collection mean map unit descriptions will provide additional detail. Where the level of detail is considered too detailed officers in conjunction with landholders and other government agencies can adjust the information to better suit the needs of pastoralists. For example 25 land units may have been described across one particular pastoral lease, all with detailed landform, soil and vegetation descriptions. The dominant grasses in each of these land units may be similar even though the landform and soils vary. All these land units can be grouped into a single pasture rating group, therefore reducing the map for example to a five coloured pasture rating map. One of the benefits of land resource information is that it can be tailored to an extremely broad range of uses, satisfying the needs of a diverse range of clients.