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

16

Some of the major climatic constraints to agricultural use in Tasmania are:

-

Uneven rainfall distribution (associated with topography, altitude and time of

year)

-

Unreliable rainfall in certain areas

-

Increasing frost hazard, lower mean temperatures and shorter growing seasons

in areas away from the coastal maritime influence

-

Occurrence of out of season frosts

-

Effect of wind in exposed areas

-

Extremes of both summer and winter temperatures affecting evaporation and

length of growing season.

Section 9 deals more fully with the available relevant climatic information pertinent

to each map sheet.

7.7

The system is based on agricultural production (cropping and pastoral productivity)

and does not take into account forestry productivity.  It is based on cultivation of the

land for cropping purposes and not other land use systems which can sustain `crops'

on steeper land with longer rotations, and less risk of erosion (e.g. perennial

horticulture, tree crops, minimum tillage crops).  Indicators of stocking rates are

incorporated where possible to support the grazing potential of the land.

7.8

The system considers degradation of the soil resource and does not take into

account the possible effects of agricultural land use on water quality, aesthetics,

wildlife, etc.

7.9

The basic principle of land capability brings together both facets of conservation -

protection of the land, and its potential production. In other words, the balance

between use of the land and the risk of degradation.

7.10

The classification, in particular at the unit level, takes into account the management

strategies and soil conservation requirements the land may need in order to maintain

a level of production without long-term degradation.

7.11

As with most land classification systems certain assumptions are necessary.  These

are:

(a)  The land capability classification is an interpretive classification based on the

permanent biophysical characteristics of the land.

(b) A moderately high level of management is being applied to the land.

(c) Appropriate soil conservation measures have been applied.

(d) Where it is reasonable and feasible for an individual farmer to remove or

modify physical limitations (e.g. high water tables, stoniness, low fertility) the

land is assessed assuming the improvements have been made.

(e) Land capability assessments of an area can be changed by major schemes that

permanently change the nature and extent of the limitations (e.g. drainage or

flood control schemes).

(f) The land capability classification is not a productivity rating for specific crops,

although the ratio of inputs to outputs may help to determine the land capability

class.

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17

(g) Land capability does not take into account economic, social or political factors

and is not influenced by such factors as location, distance from markets, land

ownership, or skill of individual farmers.

(h) Present and past uses of the land (or similar land elsewhere) are guides to

potential, in that they can indicate the limits of the capability of the land.

Present land use and vegetation cover are not always good indicators of land

capability class.  The system of land capability is aimed at assessing the

potential sustainable productivity of land rather than current productivity.

(i) Assessments are based on the capability of the land for sustained agricultural

productivity, since use of the land beyond its capability can lead to land

degradation and permanent damage.

7.12

The system is consistent across the State.

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18

8.

The Land Capability Classes

The land capability class is the broadest grouping of the land capability classification and

gives an indication of the general degree of limitation to use.

There are seven classes, arranged from Class 1 to Class 7 in order of increasing degree of

limitations or hazards to use, and decreasing degree of versatility (refer to Tables 2 and 3).

CLASS

CROPPING

SUITABILITY

PASTORAL

SUITABILITY

1

2

High

3

Medium

4

Low

High

5

Medium

6

Unsuitable

Low

Increasing Limitations to Use

7

Unsuitable

Decreasing Versatility

Table 2

:

Suitability of different land uses for land capability classes.

Adapted from: National Water and Soil Conservation Organisation, 1979, Our Land Resources. (NWASCO),

Wellington, New Zealand.)

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19

Table 3:

Features of land capability classes.

The criteria used to define the classes are based on observation and experience only, and

not on experimental work.  Where necessary, soil physical and chemical criteria have been

tested in a laboratory situation.

In time, it may be necessary to refine or modify the criteria for the different classes to

incorporate changes in technology and increased understanding about the interactions

between soils, farming practices and the natural environment.  It is anticipated that the

guidelines to the classes will be revised, where relevant, to incorporate this new

information.

U

n

d

er

 cu

lt

ivati

o

n

U

n

d

er

 p

a

storal

 u

se

CLASS

LIMITATIONS

CHOICE OF

CROPS

CONSERVATION

PRACTICES

1

7

6

5

4

3

2

Severe

Grazing

Grazing

No, or very

minor

agricultural

value

Major

+

careful

management

Very minor

Medium

Severe

Slightly

reduced

Minor

Very minor

any

Slight

Reduced

Major

Restricted

Very severe

to

extreme

Slight

to

moderate

---