Replacement of deep-rooted, perennial native vegetation with shallow-rooted,
annual agricultural plants has resulted in increased recharge causing shallow
saline water tables leading to dryland salinity and loss of agricultural
production. Restoring the vegetation by regeneration or replanting lowers
water levels locally but field evidence and computer modelling suggests this
needs to be widespread for regional effects, which conflicts with the future
of conventional agriculture. Alley farming allows agriculture to be continued
in the bays between the rows, but needs as much perennial, preferably
deep-rooted, vegetation as possible in the bays to achieve the required
recharge reductions.
Where the asset to be preserved is valuable and a means of safe saline
effluent disposal exists, pumps and drains will be part of any salinity
management system, but where these conditions are not met they will be of
limited use on an economic basis.
To limit the spread of dryland salinity substantial change in farming systems
is required and farmers need assurance that the recommended strategies will
have the desired effect. Computer modelling is the only timely way to do this.
An operationally simple 1-dimensional model already exists, and a
2-dimensional one is under development and testing. Three-dimensional
modelling is also probably required to support strategic, intensive
interventions.
computer modelling, revegetation, engineering, perennial.
At a sandplain seep at East Belka in the Western Australian Wheatbelt, saline groundwater discharge occurs from a shallow (approx. 2 m) perched aquifer of moderate permeability (0.15 m day-'). Groundwater qualities range from over 2,500 mS m -I in the saline area, to between 660 and 1,700 mS m-' in the plantation. In 1986 five varieties of eucalypts (E. globulus, E. dadocalyx var. nana and three provenances of E. camaldulensis) were planted across the contour upslope from the seep on about 1-0 per cent of the catchment. By 1989 the seedlings had grown to heights of up to 6.5 m. Despite above-average rainfall over the study period, perched water-tables under the plantation and seep were progressively lowered (approx. 0.5-1.0 m) until the area was dry a t the start of the 1989-1990 summer. Wheat (Triticum aestiuum) established on the seep and adjacent paddock in May 1989, provided a yield of over 1.0 t ha-' on a site that had been unproductive for 20 years.The method has the potential to reclaim much of the existing eastern and northern wheatbelt where there are salinity problems caused by perched groundwater, and could prevent recharge of the regional aquifer beneath the sandplain seep. However, additional techniques will be required to prevent deep aquifer discharge caused by steadily rising (approx.0.1 5 m yr-') regional water-tables. Discharge and associated dryland salinity from the regional system are expected to be major problems during the next 40 years at the site investigated.
We investigated why the Wallatin Creek Catchment in the Western Australian wheatbelt had an appreciable area of secondary salinity whereas the adjoining North Baandee Catchment had almost none. The Wallatin Creek Catchment, which is long and narrow, had a shallow regolith over granite bedrock. Although this catchment had less salt stored in the regolith than the wider North Baandee Catchment, the groundwaters came close to the ground surface because the regolith was thin and the valley cross-section narrow. Management practices which increase recharge (e.g. using level banks to control runoff), are likely to result in increased salinity in the short term in the Wallatin Creek Catchment. We also investigated whether retaining areas of remnant vegetation had reduced the amount of secondary salinity in a sub-catchment of the Wallatin Creek Catchment. At comparable positions in the landscape, groundwater levels were up to 7 m lower under the remnant vegetation. The vegetation appears to have delayed, if not prevented, the development of salinity in nearby and downslope areas.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.