Dealing with salinity in Wheatbelt Valleys - Department of Water

non-financial benefits other than for salinity need
to be sufficient.)
In the past, the interdependence of farmers within
a large catchment has been emphasised. At least
with respect to movements of groundwater,
Wheatbelt farmers are now seen to be much less
dependent on each other for groundwater
management. Importantly, it is now known to be
possible for groundwater management to be
effective locally, at least temporarily, even without
cooperation from neighbours. Typically, soils in
the large wheatbelt valleys of Western Australia
have low “transmissivity”, meaning that little water
passes through them. This, combined with the
very low slopes, means that lateral water
movement is very slow indeed and transmission of
pressure is low. Even if equilibrium areas of
salinity are reduced (as in parts of Figure 1), the
planting of large areas of perennials is likely to
delay the process of reaching that equilibrium by
between 20 and 80 years (Campbell et al. 2000).
This delay is worth money directly, and it may also
buy time for better management options to
become available.
But the treatments still need to generate money
directly. The availability of perennial options
which can generate an income will be critical for
our future salinity management in the Wheatbelt.
A big effort to prove (and improve) lucerne is
underway. The other option on the horizon is oil
mallees. Oil mallees appear likely to become
profitable for farms located within the transport
limits of processing plants/power generators
(Bartle 1999; Cooper 2000; Herbert 2000). A
pilot plant is planned for the town of Narrogin.
However it is clear that we will need many more
options that these two. The new Cooperative
Research Centre for Plant-Based Management of
Dryland Salinity has as its prime objective the
development of new profitable plant based options
for salinity management.
Living with salinity
Farmers with large areas of salt-affected land are
already trialling and implementing farming systems
based on salt-tolerant species (e.g. salt bush, blue
bush). In addition, there is growing interest in
economic uses for saline water (e.g. aquaculture,
electricity generation, irrigation with brackish
water, algae [e.g. for agar, β-carotene, pigments,
fish food], seaweed) and the potential to extract
valuable salts and minerals (e.g. magnesium,
bromine, potassium chloride) (see
– 5 –
Pannell
http://www.ndsp.gov.au/opus/menu.htm for the
OPUS database, accessed 5 June 2001).
There has been little recent economic analysis of
these practices (which seems an important
oversight). However, there is reason to expect
that they will become of considerable economic
importance. Much of the forecast salinisation of
land is not technically avoidable without
implausibly large changes in land use. The plantbased
options for saline land have at least one
advantage over perennials planted in recharge
areas. Recharge areas are still productive and
valuable for traditional production, so farmers will
be reluctant to switch to other land uses unless
they are about as profitable. Establishing salttolerant
species on salt-affected areas does not
involve the same sort of sacrifice. Therefore,
provided that up-front establishment costs are low
enough and/or adequate productivity can be
demonstrated, the prospects for widespread
adoption of new salt-tolerant plants for economic
production on salt-affected land appear good.
Another advantage is that feed availability from
salt-tolerant pastures can be timed to reduce the
autumn feed gap, and therefore to increase yearround
stocking levels. This remains an advantage
so long as the area of salt-tolerant pastures is not
so great as to more than fill the feed gap.
Repairing salinity
Many farmers would prefer to repair salinised land
and continue with traditional agriculture, if that is
possible. This requires engineering. Deep open
drains have been installed by many farmers to
enhance discharge. Measurements by researchers
have found that they reduce groundwater levels
within only a few metres of the drain on high-clay
soils and rarely more than 40 metres on favourable
soils (George 1985; George & Nulsen 1985;
Speed & Simons 1992; Ferdowsian et al. 1997).
However farmers have observed positive effects of
deep drains on plant growth over greater distances
than this. It is not clear whether these effects at a
distance are due to reductions in groundwater
levels or reductions in water logging (which could
probably be achieved with much cheaper
structures). An economic analysis of deep open
drains on agricultural land by Ferdowsian et al.
(1997) reached negative conclusions about their
cost effectiveness, but given farmer observations
and new evidence that is emerging about their
effectiveness in some situations, further research
and analysis is needed. A key issue to resolve with
deep drainage is the cost-effective and
environmentally safe disposal of discharged waters.