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.
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.
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.)
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