Irrigation - Australian Agriculture Assessment 2001 - Appendix 3 - Vertosols
VERTOSOLS
Vertosols are clay soils (>35% clay) with shrink-swell properties which cause deep and wide cracking on drying. Lenticular structure and slickensides are diagnostic features. The soils vary in colour – black, brown, grey and red with every gradation in between – and range from strongly acid to highly calcareous. Australia has a greater area and diversity of Vertosols than any other country.
Black Vertosols
Black Vertosols are one of the most highly productive soils for agriculture in Australia. A typical example of a Haplic, Self-mulching, Black Vertosol with a self-mulching surface (strongly pedal loose surface mulch) is described below.
Environment
Distribution: Occur discontinuously from Tasmania to the Kimberleys. The most important agricultural areas are in subhumid eastern New South Wales and subtropical Queensland. Strikingly uncommon in virtually all of Western Australia except the far north.
Climate: Mean annual rainfall ranges from 500 mm to 1000 mm, is summer dominant in the north and winter dominant in the south.
Parent materials or substrate: Most common on basic igneous rocks such as basalt and dolerite, lithic and felspathic sandstones and shales, and derived alluvial and colluvial sediments.
Landform: Level to undulating plains, hillslopes and undulating rises.
Native vegetation: Grassland, open eucalypt woodland and Acacia open forest.
Land use
Winter grain and oilseed crops (often with bare fallowing) dryland cereals, sunflower and irrigated cotton in the summer. Grazed native pasture in regions of unreliable rainfall and steep slopes.
Common variants
Black Vertosols may range in depth from 0.30 to 2.00 m. Calcareous segregations may occur higher in the profile (Endocalcareous or Epicalcareous) in association with gilgai microrelief. Massive or coarsely structured soils and profiles with a pedal soil surface condition may also occur. Aquic types occur in the backswamps and depressions of some northern coastal plains.
Nomenclature
Also known as Black Earths and Black Cracking Clays.
Soil qualities
Water availability: Moderate (150 – 200 mm).
Drainage: Initial rapid infiltration via cracks but imperfectly drained when wet.
Aeration: Generally adequate but compacted layers may be restrictive, particularly when irrigated.
Physical root limitations: Plough pan development will limit root growth.
Erosion hazard: Serious on slopes in high intensity rainfall regions (tropics and subtropics).
Nutrient availability: Nitrogen levels decline under cropping. Commonly deficient in sulphur and zinc.
Toxicities: Secondary salinity may be a problem.
Workability: Self-mulching properties enhance soil surface condition. Plough pan due to compaction of wet soil will reduce workability.
Acknowledgment
Photo, soil description and laboratory data from Queensland Department of Natural Resources.
Typical profile
Eastern Darling Downs, Queensland. |
Soil description of a typical profileA1 0 – 0.03 m Black (10YR 2/1) medium clay; strong fine granular structure; self-mulching; moderately moist, firm consistence; abrupt boundary to: B21 0.03 – 0.20 m Black (10YR 2/1) medium heavy clay; strong subangular blocky parting to fine granular structure; moderately moist, firm consistence; clear boundary to: B22 0.20 – 1.10 m Black (10YR 2/1) medium heavy clay; strong blocky parting to moderate lenticular structure; some slickensides; tongue of brown clay with carbonate at 0.90 m; moist, firm consistence; abrupt boundary to: B23 1.10 – 1.75 m Brown (7.5YR 3/4) medium heavy clay; strong blocky parting to moderate lenticular structure; moist, firm consistence; 2 – 10% soft, calcareous segregations. |
Laboratory data for the typical profile
Grey Vertosols
These are probably the most widespread and diverse of all Australian Vertosols. Many are extremely deep (up to 6.0 m) and have a very pronounced gilgai microrelief. The Epicalcareous-Endohypersodic, Self-mulching, Grey Vertosol described below has a surface horizon that is self-mulching (strongly pedal loose surface mulch) and a calcareous and strongly sodic subsoil.
Environment
Distribution: Largely confined to the eastern States (except Tasmania) and the Northern Territory, occupying large continuous areas in western Queensland.
Climate: Essentially soils of the arid and semi-arid regions. Mean annual rainfall is 600 mm or less.
Parent materials or substrate: Most extensively derived from lithic sandstones, mudstones, shales and alluvial and colluvial sediments derived from these and more basic igneous rocks.
Landform: Level to undulating plains and vast inland floodplains subject to sporadic major flooding.
Native vegetation: Grasslands and sparse, low shrublands in arid regions. Open woodland and originally extensive Acacia open forests in more humid areas.
Land use
Climate is a major influence. Irrigated cotton, rice and pastures in New South Wales and Queensland. Grazing in the arid zones. Dryland cereals and grain legumes in most eastern States. Bare fallowing to allow winter crops in areas of unreliable rainfall.
Common variants
Other soils may have a thin, crusty surface (< 0.03 m); massive structure; coarse blocky or pedal non self-mulching A horizon. Various forms and amounts of subsoil carbonate occur with gypsum in the more arid varieties. In eastern Queensland and northern New South Wales strongly acidic subsoils are a distinctive feature. Aquic types occur on some high rainfall coastal plains.
Nomenclature
Commonly known as Grey Clays.
Soil qualities
Water availability: Low to moderate (75 – 150 mm) depending on depth of chemical or physical impeding layers. Low infiltration can restrict filling of soil water storage.
Drainage: Initial rapid infiltration via cracks but imperfectly drained when wet.
Aeration: Can be restrictive, particularly when irrigated, compacted or both.
Physical root limitations: A plough pan and a strongly dispersive subsoil may restrict water and root movements.
Erosion hazard: Serious on slopes in high intensity rainfall regions (tropics and subtropics).
Nutrient availability: Nitrogen and phosphorus decline with cultivation. Possible zinc deficiency in strongly alkaline soils.
Toxicities: Subsoils may be strongly saline.
Workability: Self-mulching properties enhance surface condition. Sodic, crusty or massive surface soils may cause workability problems
Acknowledgment
Photo, soil description and laboratory data from Department of Natural Resources and Environment, Victoria. Site 8 Wimmera.
Typical profile
Horsham district, north-west Victoria. |
Soil description of a typical profileA1 0 – 0.05 m Dark greyish brown (10YR 4/2) light clay; moderate granular structure; self-mulching; <2% hard carbonate nodules; dry, soft consistence; sharp boundary to: B21 0.05 – 0.25 m Dark greyish brown (10YR 4/2) light medium clay; moderate very coarse prismatic structure; dry, firm consistence; moist, slightly sticky consistence; <2% hard carbonate nodules; gradual boundary to: B22 0.25 – 0.60 m Dark greyish brown (10YR 4/2) heavy clay; moderate very coarse prismatic structure; dry, firm consistence; moist, slightly sticky consistence; <2% hard carbonate nodules; gradual boundary to: B23 0.60 – 1.20 m Greyish brown (10YR 5/2) heavy clay; weak coarse blocky structure; dry, firm consistence; moist, slightly sticky consistence; slickensides; <2% hard carbonate nodules; sharp boundary to: B3 1.20 – 1.75 m Brown (7.5YR5/4) changing to yellowish red (5YR 5/6) medium clay; dry, firm consistence; moist, slightly sticky consistence; slickensides; <2% hard and soft carbonate nodules. |
Laboratory data for the typical profile
Brown Vertosols
Brown Vertosols are very similar in their properties to the grey forms, into which they commonly grade. Many are deep but gilgai microrelief is less strongly developed and less extensive. A typical example of a Haplic, Epipedal, Brown Vertosol is given below.
Environment
Distribution: Major areas are in the arid zone where they are commonly associated with Red Vertosols.
Climate: The largest areas occur in the arid zone with less than 500 mm mean annual rainfall.
Parent materials or substrate: Most extensively derived from lithic sandstones, mudstones and shales and alluvial and colluvial sediments derived from these rocks.
Landform: Level to gently undulating plains are most common.
Native vegetation: Tussock grasslands and sparse low shrublands. Some more humid regions in eastern Australia originally carried Acacia open forest.
Land Use
Cattle and sheep grazing of native pastures. In humid regions practices are similar to Grey Vertosols.
Common variants
Otherwise similar soils may be self-mulching or have a thin crusty surface soil. Carbonate may occur throughout and subsoils may be strongly saline and sodic. Soils in the arid zone usually contain variable amounts of gypsum.
Nomenclature
Also known as Brown Clays.
Soil qualities
Water availability: Moderate (100 – 150 mm) depending on depth of chemical or physical impeding layers. Low infiltration may restrict filling of soil water storage.
Drainage: Initially rapid via cracks. Low to moderate when wet and if surface soil is dispersive.
Aeration: Can be restrictive, particularly when irrigated, compacted or both.
Physical root limitations: Restricted by sodic and strongly alkaline subsoil if present.
Erosion hazard: Serious on slopes in high intensity rainfall regions and dispersive surface soils.
Nutrient availability: Nitrogen and phosphorus decline with cultivation. Possible zinc deficiency in strongly alkaline soils.
Toxicities: Some arid soils may be strongly saline.
Workability: Good, providing the soil is not overworked, compacted when wet or strongly dispersive. Self mulching properties will improve workability.
Acknowledgment
Photo, soil description and laboratory data from Department of Natural Resources and Environment, Victoria. Site LP 95.
Typical profile
Charlton district, northern Victoria. |
Soil description of a typical profileA1 0 – 0.10 m Dark brown (7.5YR 3.5/4) light medium clay; moderate coarse blocky structure; dry, firm consistence; abrupt boundary to: B21 0.10 – 0.70 m Dark brown (10YR 3/3) medium heavy clay; coarse prismatic parting to strong coarse blocky structure; dry, very hard consistence; clear boundary to: B22 0.70 – 1.20 m Brown (10YR 4/3) medium heavy clay with strong brown (7.5YR 5/6) diffuse mottles; moderate coarse prismatic parting to moderate coarse blocky structure; dry, firm consistence; abrupt boundary to: C 1.20 m+ High amounts of soft carbonate. |
Laboratory data for the typical profile
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