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

46

Class 1 land occurs in areas of favourable climate in the northern half of the map.  These

areas have a mild maritime climate with less seasonal variation in temperatures compared

to areas inland, and a low incidence of frost.  Frosts do occur in some areas during winter,

however they are generally not a significant hazard to cropping use.  Although rainfall is

around 800 - 900 mm per annum, any moisture deficits during the growing season can be

boosted by on-farm water supplies for irrigation.

The range of crops that can be grown on Class 1 land is the most extensive for any area in

Tasmania.  Crops include berry fruits, pyrethrum, essential oils, all vegetable and allied

crops, cereals, fruit, flower crops and forage and green fodder crops.  Yields are

consistently high for all crops, and can be boosted further by fertiliser and irrigation inputs.

Class 1 land on basalt is the most versatile land in Tasmania.  Because of the excellent soil

structural properties, these areas can be cropped intensively.  However they still require

periods out of cultivation (pasture phases) to maintain soil structure.  Compaction by

cropping machinery and soil structural decline are potential forms of land degradation on

this type of land, and should be monitored closely.

Table 8 summarises the major features of the land capability classes on basalt, according to

slope, stoniness and climatic limitations.

Photo 4:

Class 1 land on basalt (foreground). Class 2 land on basalt in background. Tamar map 589295.

Brierley Grove Road.

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47

CLASS

SLOPE

CROPING

VERSATILITY

CLIMATIC

LIMITATION

STONINESS

LIMITATION

EROSION TYPES

(under cultivation)

SOIL MANAGEMENT

MEASURES

REQUIRED

(under cultivation)

LENGTH OF

CROPPING

PHASE

(years out of 10)

LIMITATIONS TO

AGRICUALTURAL

USE

1

0-5%

All annual crops

Nil

Nil

Nil to slight sheet and

rill

No special management

practices

8-9 years

None

2

5-12%

All annual crops

Nil

Nil

Slight to moderate sheet

and rill

Minor conservation

works

5-8 years

None

2

0-5%

All crops except

frost tender

Slight

Nil

Nil to slight sheet and

rill

No special management

practices

8-9 years

Climate

2

5-12%

All crops except

frost tender

Slight

Nil

Slight to moderate sheet

and rill

Minor conservation

works

5-8 years

Climate

3

12-18%

All annual crops

Nil

Nil

Moderate  sheet  and  rill,

slight gully

Major conservation

works

2-5 years

Slope

3

5-12%

Slightly restricted

range of crops

Nil

Moderate

Nil to moderate sheet

and rill

None to minor

conservation works

2-8 years

Stoniness

3

12-18%

Restricted range of

crops

Slight to

moderate

Nil

Moderate sheet and rill,

slight gully

Major conservation

works

2-5 years

Climate, slope

3

0-12%

Restricted range of

crops

Slight to

moderate

Moderate

Nil to moderate sheet

and rill

None to minor

conservation works

2-8 years

Stoniness, climate

4

18-30%

Restricted range of

crops

Nil

Nil

Severe sheet, rill and

gully

Major conservation

works

1-2 years

Slope

4

0-18%

Restricted range of

crops

Nil

Moderate to

severe

Nil to moderate sheet

and rill, slight gully

None to major

conservation works

2-5 years

Stoniness

4

18-30%

Restricted range of

crops

Slight to

moderate

Nil

Severe sheet, rill and

gully

Major conservation

works

1-2 years

Climate, slope

4

0-18%

Severely restricted

range of crops

Slight to

moderate

Moderate to

severe

Nil to moderate sheet

and rill, slight gully

None to major

conservation works

2-5 years

Stoniness, climate

Table 8:

Features of land capability classes on basalt according to slope, stoniness and climatic limitations.

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48

10.2 Class 2 (604 ha; 0.33%)

Class 2 land on basalt

Class 2 land on basalt has been mapped in the Thirlstane and East Sassafras areas, and at

High Plains (south of Weetah).

The basalt soils (krasnozems) are similar to those described in Section 10.1.  However

slopes on Class 2 land are steeper than on Class 1, and can range up to 12%.

To preserve the excellent soil structure and the long-term potential of this land for

cropping, Class 2 land should not be cropped in rotation for more than five to eight years,

in a ten year cycle.  Soils are generally stable, particularly under pasture.  When under crop,

minor soil conservation works such as graded drains may be necessary to limit sheet and

rill erosion.  Compaction by cropping machinery also needs to be limited in order to

prevent compaction of topsoils which may result in decreased infiltration rates.

At present the areas of Class 2 land on basalt are used for intensive cropping, in particular

vegetable crops.  The range of crops able to be grown are the same as those mentioned for

Class 1 land, excluding however the area at High Plains, which experiences a much higher

incidence of frost.  The risk of out of season frosts and shorter growing seasons in

comparison to the Thirlstane and East Sassafras areas, slightly reduce the range and yields

of crops that can be grown here.  For this reason i.e. climatic limitation, this area of land

has been classified as Class 2.

Average annual rainfalls are between 800 and 900 mm for the Thirlstane-East Sassafras

area, and around 1 000 mm at High Plains.

Refer to Photo 5 which shows a typical example of Class 2 land on basalt, and Table 8

which summarises the major features of the land capability classes on basalt, according to

slope, stoniness and climatic limitations.

Photo 5:

Class 2 land on basalt. Tamar map 584288. Bass Highway.

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