Tamar report land Capability Survey of Tasmania k e noble 1992 Tamar Report

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Association

Dominant Soils

Soil Profile

Landscape Features

Parent Materials

STOCKPORT

(Sp)

Generally fine textured

hydromorphic soils,

sometimes saline; small

areas of groundwater

podzols

Dark crumbly silty clay loam or clay loam; over

dark grey blocky clay; over mottled dark grey

and olive brown plastic clay

Lagoon floors with small areas

of super-imposed sand dunes

? Pleistocene or Recent

swamp deposits - clays

and some gravels

SUPPLY

(S)

Fine textured hydromorphic

soils

Dark grey silt loam, silty clay loam or fine

sandy clay loam; over mottled dark grey or

yellowish brown clay, silty clay or fine sandy

clay over grey clay

Mainly present day floodplains

but includes some older terrace

remnants

Recent alluvium - fine

sandy clay and silty clays

TAMAR

(Tm)

Saline grey soils usually fine

texture

Dark organic clay or sandy loam; over light

sand and sandy clay to grey sticky clay; over

dark grey sticky clay

Low-lying waterlogged flats

less than 5' above H.W.M.

Recent estuarine deposits

- clays and some sands

TATANA

(T)

Podzols

Dark grey to light brownish grey sand with

organic matter; over light brownish grey sand;

over mottled yellowish brown, olive brown,

dark brown loose sand

Very gently undulating to easy

rolling. General absence of rock

outcrops

Permian  and Triassic

siliceous sandstones

VULCAN

(V)

Lateritic krasnozems and

other soils

Reddish brown fine sandy loam; over reddish

brown fine sandy clay loam; over dark red and

weakly mottled red clay

Easy rolling to rolling. Much

ironstone gravel on surface; a

few strong outcrops of "iron

ore" capping low hills

Cambrian ultrabasic

rocks

WARRINA

(W)

Yellow podzolic soils

Fine  sandy  loams, sandy loams or silt loams;

over mottled light yellowish brown, brown and

grey fine sandy clay loam; over bright grey with

strong brown and red mottling, sandy clay

Very gently undulating to

rolling or hilly, up to about 500'

elevation

Permian mudstones and

siltstones

YORK TOWN

(YT)

Podzols and yellow podzolic

soils

Black to very dark grey loamy sand; over grey

to light grey to greyish brown sand; over

mottled yellowish brown clay

Gently undulating to easy

rolling marine (?) plain, sloping

from about 180' to 80' or 90'

Tertiary clayey and

gravelly sediments

Key to soil associations (cont)

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45

10. Description of Land Capability Classes on 

Tamar Map

The following sections describe the different types of land which have been mapped in the

seven land capability classes found on the Tamar map.  The complexity of the pattern of

land capability mapped is a reflection of the complex geology, soil types and topography

found on this map.  A stylised cross section of the West Tamar area showing landform,

geology, soil and land capability relationships is shown in Figure 11, at the end of this

section.

The majority of land mapped on the Tamar map is Class 4 land, followed by Class 5 and

Class 6.  The area and percentages of land on the Tamar map is shown in Tables 1 and 9.

10.1 Class 1 (42 ha, 0.02% of Tamar map land area)

Class 1 land on basalt

One area of Class 1 land has been mapped on soils from basalt (krasnozems) at Brierley

Grove, west of East Sassafras.  Another area east of Thirlstane has been mapped as a

complex of Class 2 and Class 1 land.  An example of Class 1 land on basalt is shown in

Photo 4.

The krasnozem soils have been formed on basalt flows which were extruded in Tertiary

times as a result of volcanic eruptions.  They are deep, well structured and free draining

soils, suitable for intensive cropping use.

Typical krasnozem soil profiles have a strong granular structured, dark red or reddish brown,

friable, clay loam A horizon; over a well structured, dark red brown to red brown, friable,

clay B horizon; grading to reddish, friable clay with increasing amounts of weathered basalt.

Soil depths are commonly greater than one metre.  Topsoil pH levels are moderately acid,

ranging between 5.0 and 6.5, and stay more or less constant with depth.  Because the soils

are free draining and have a strongly developed granular structure, they are easy to work

over a wide range of moisture conditions.  Organic matter content is high in the surface

horizons, and needs to be maintained by the use of green manure crops.  This would help

maintain the excellent soil structure and retain minerals essential to plant growth.

Topsoil erosion and leaching, particularly in deeply weathered basalt profiles, can result in a

loss of nutrients such as calcium, potassium, sulphur, magnesium and nitrogen.  These losses

can be combatted by the accumulation of nutrients in organic matter in the surface horizons.

Phosphorous and molybdenum retention are also common problems on krasnozem soils, and

can be combatted by the application of lime and mineral fertilisers (superphosphate and

molybdenum super).

Because most of the available nutrients are held in the topsoil, it is extremely important that

this topsoil layer be preserved.  If lost through erosion, an important part of the nutrient

supply is lost.  The subsoil horizons lack a high level of available nutrients and higher levels

of fertiliser application are required to maintain production.

Class 1 land on basalt can range up to 5% slope.  This may include areas of flat land or areas

which receive runoff from surrounding slopes, which may require minimal drainage to

prevent waterlogging or the accumulation of surface water.  Where this is not possible, these

areas may be downgraded to Class 2 land.

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