Today, soil salinization is a significant form of soil degradation in the state's agricultural areas. Implementation of salinity control measures on a catchment basis requires that the hydrologically significant areas in the catchment be defined.
Introduction
Historical Review
Details of the soil survey in the Salmon Gums district have yet to be published (Burvill, private communication). Research was carried out in the East Perenjori catchment and in part of the Kent River catchment.
The Cause and Nature of the Salt Problem
- Source of the Salt - Rainfall
- The Accumulation in Soil of Salt from Rainfall
- Soils, Topography and Hydrology
- Soil Factors Influencing Salt Accumulation
- Parent Material and Naturally Saline Soils
- The Influence of Topography on Soil Salinity
- Slope
- Dissection
- Micro- topography
- Hydrology and Salinity
- Effect of Land Use on Salinity
- Salt Movement and Accumulation in Soil and Groundwater
- Effect of Soil on Salt Movement and Accumulation
- Salt and Water Imported in Groundwater
- Movement of Water Under Pressure
- Capillary Rise and Critical Depth
The importance of vegetation removal was thus recognized very early in the development of the salt problem. There was also a gradient of increasing salinity from the highest point in the landscape to the valley floor.
Extent of Salinity in Western Australia
Australian Bureau of Statistics 1984 Saltland Survey
Previous Results 1962-1979
The 1984 Survey and Results
South West Division
Southern Agriculture Division
Central Agriculture Division
Northern Agricultural Division
Eastern Goldfields, Central and North West Divisions
The average salt area on each affected farm was highest in Lake Grace at 120ha and Dumbleyung at 114ha.
Results Summary
Discussion of Survey Results
Shows holdings, clearings and salt land totals in the statistical division in the 1984-85 Saltland Survey.
Conclusions
Regional Assessment of Potential for Land Salinization
Northern Agricultural Region
Current Status
Potential Area
However, there have been recent outbreaks near Coomallo Creek and, given the experience of. Based on the above, it is estimated that the potential area at risk from salinization is about 600,000 ha.
Strategies
Central Agricultural Region
Current Salt-Affected Areas
The Potential Area Which Could Become Saline
Knowledge of the hydraulic properties and behavior of aquifers before clearing and now can be used to calculate water balances for groundwater systems. However, Peck and Hurle (1973) suggest it may be on the order of hundreds of years in the Darling range to thousands of years in the central and eastern wheat belts. Based on knowledge of the charge rates and areas, and discharge rates and areas, an estimate can be made of the area potentially affected.
Current estimates suggest that recharge rates are two to three orders of magnitude higher than before deletion. Using estimates of discharge rates from saline soils, it is estimated that 10-20% of the landscape may be prone to groundwater discharge and salinity. Field observations in highly saline watersheds confirm that up to 20% of the watershed is required to balance the input supply.
This may be what could be expected in many central wheat belt valleys and eventually in all valleys unless management strategies are adopted to control its spread.
Time to Develop the Full Potential
Groundwater systems and water table levels are currently changing in response to clearing of native vegetation and consequent reduction in evaporation caused by new agricultural systems. In these catchments highly saline soils occur throughout the valley floor and have migrated upslope at the head of the main valleys. A projection time frame would place major salinization in the central wheat belt within the next 0-100 years and within the eastern wheat belt between 50-200 years.
Strategies Available for Saltland Control
Although the list is not exhaustive, it contains many of the techniques currently available that are worthy of consideration for every major soil salt problem in the region. Farmers must consider each alternative on each soil-landform, and will likely choose several for each. A total of more than 100 procedures can be adopted by any individual farmer to reduce a salinity problem in the catchment.
In cases where individual farmers do not manage the entire watershed that affects their property, Soils on the catchment or slope Soils on the middle slope Soils on the lower slope Soils in the valley Soils and relief units* Ulva. The final advice and strategies will depend on the position of individuals within the catchment, the participation of the group of farmers and the local hydrogeological and geomorphic characteristics.
The landform units describe 11 of 14 major provinces recognized in the Merredin Soil Conservation Manual in preparation.
Great Southern Region
North Stirling Basin It is estimated that approximately 10% of the basin's 50,000 ha area is currently affected by salt. The current salt-affected area in the Great Southern District appears to be greater than the 2% recorded in the 1979 and 1984 censuses, and is probably in the 5-10% range. Salinity is likely to spread from drainage lines to slope breaks in valleys, up to drainage lines on valley sides, and seepage of levees and rock bars is likely to increase.
For the Great Southern district, it is possible that between 30 and 50% of the cleared land may be salt-affected. With 'average' rainfall and current land use, around 70% of the potential area could be affected within 20 years, and 95% of the potential area within 30 years. Farmers concentrate too much on treating the salt land and not enough on the rest of the catchment (this is where the problem is caused).
In general, more research is needed to define the most appropriate and economical approach in specific areas.
South West Region
Lack of knowledge about the hydrology of the salinity problem hampers the formulation of further management options. Furthermore, there is no precise local experimental data that allows determining the optimal frequency of irrigation or the amount of water required to "replenish" the soil with each irrigation. Only by improving the overall production of the agricultural system will the farmers be able to do what is necessary.
A feasibility study before the project started showed that the rehabilitation of the canals was more expensive. Under permanent pastures, the water table should be maintained between 1.0 and 1.2 m below the surface (Lyle 1984) to prevent surface salinization over the summer. The establishment of an open market in irrigation water should, in theory, lead to overall improved productivity of irrigated areas by shifting water use to more efficient managers and to more productive and less saline soils.
Currently, the overconcentration of irrigation activity is prevented by the even geographical distribution of water allocations throughout the irrigation areas and the limitation of irrigation ratings to one third of the farm.
South Coast Region
There is some application of high water use land use strategies (eg alfalfa) in the area. A number of farmers are planting trees, some have installed surface and deep drains; some plant salt-tolerant pastures. Methods are available to identify the -landscape units and progress has been made in designing successful establishment methods of trees and perennial pastures.
The Cost of Land Salinization
Salinity Research 1987/1988-
Catchment Hydrology
To measure the effectiveness of shallow surface drains at various spacings in removing excess rainfall from heavy clay plains in Western Australia. To understand the distribution of salt affected areas in different valley systems in the Kellerberrin Soil Conservation District. TITLE: Seepage interceptor drains for clogging control in grain growing areas in Western Australia.
To determine the physical extent and economic significance of waterlogging in the Upper Great South. TITLE: The effect of alfalfa grazing on the groundwater hydrology of a small catchment in the Esperance area. To determine options available for treating the soil salinity in the catchment and the salt discharge into the Kent River.
17 TITLE: Identification and Characterization of Recharge Zones Associated with Secondary Salinity in the Upper Great Southern.
Land Drainage
To assess and develop practical methods of drainage for waterlogging control on duplex lands in the high rainfall areas.
Saltland Agronomy
These experiments are part of the Atriplex species and ecotype screening program for improved production on salt-affected land. Their purpose is to identify and assess the survival and growth of a species of saltbush planted as seedlings in the field. This trial is part of a program to screen Atriplex species and ecotypes for improved forage production on salt-affected soils.
This trial is part of a program to screen Atriplex species and ecotypes for improved production from salt-affected soils. To compare six accessions of Atriplex amnicola for establishment on a saline fire in the pastoral zone. To define and quantify the hydrological systems operating on a lake in the North Stirling SCD.
To determine the effect of black latex paint coating treatment on the establishment of Atriplex amnicola, A.
Waterlogging
Agroforestry
To determine the effect of trees planted in an agro-forestry plan on saline groundwater. To evaluate Tagasaste as an alternative to replanting parts of the Wellington Dam catchment back to eucalypts, thereby maintaining the same agricultural productivity in the region. In order to achieve this goal, a number of secondary goals must be realized:. a) evaluate Tagasaste as a fodder tree;.
One of the declared objectives of the Salinity and Hydrology Research Branch is "To identify and quantify the causes of salinity and determine appropriate watershed management strategies to obtain production from the affected area, prevent spread of the affected area and mitigate external to reduce the effects of salinity". (Annual Report of the Commissioner for Soil Conservation and Resource Management Department, Ministry of Agriculture 1986/87). This control of the landscape water balance must be achieved while maintaining the productivity of the land; whether that be productivity in terms of agricultural products, water resources or public utilities. With specific reference to salinity, the catchment area is roughly divided into two units: a drain area where the vertical component of the hydraulic gradient is upwards, and a recharge area where the vertical component of the hydraulic gradient is downwards.
Nulsen (1984) in detailing the catchment approach to saline land management refers to the discharge area as "in situ" ie.
Water is the Real Problem
Obviously, there are no simple solutions to soil salinity; the solutions lie in addressing the landscape water balance by reducing recharge and increasing discharge. Effective management, however, requires an understanding of the processes that occur and an understanding of where in the landscape these processes take place.
Problem Definition
The Importance of Catchment Management
Management of Recharge Areas
Strategic Clearing
Replanting Trees and Shrubs
High Water Use Crops and Pastures
Tillage Practices to Maximize Crop Water use and Minimize Run-off
Fertilizer Regimes to Maximize Crop Water Use
Management of Discharge Areas
Drainage
Trees as Pumps
Production from Halophytes
Site Severity
Waterlogging and Flooding
Salt Content and pH of Soil
Salt Tolerant Plants for Grazing
It is sensitive to watering, so it should not be planted if there is a risk of flooding for more than two to three days. Branches can form roots where they lie on the ground, helping to recover from grazing and control soil erosion. All are very tolerant of salt and waterlogging and will grow to the edges of salt lakes.
Many farmers across the country are planting and using salt-tolerant shrub and pasture species. Samphire is grazed in autumn in conjunction with eight neighboring stubble fields and is a valuable forage reserve. This is equivalent to 2,510 days of sheep grazing per hectare, all at a time when other forage was extremely scarce.
Diamond of Maya has established 200 acres of wavy leaf salt bush over the past six years.
Conclusion
Salinity content of lateritic profiles in the Yarragil catchment W.A. SALINITY IN WESTERN AUSTRALIA – A SITUATION STATEMENT. Water Research Foundation Seminar “Water Quality and Its Significance in Western Australia”, Murdoch University, October 1983. Plant collection for pasture improvement in saline and arid environments W. SALINITY IN WESTERN AUSTRALIA – A SITUATION STATEMENT.
