Soil Salinity - Page 8
How do I manage soil salinity?
Primary salinity
Adopt salt tolerant crop and pasture varieties
Use crops and pastures (e.g. cotton, barley, couch grass) that are less prone to the adverse effects of salinity than others (e.g. beans, apples, clovers).
Management of salt affected areas
Where saline areas have been identified, fence them off to control stock access. Often improvements in pasture cover can be achieved just through the exclusion of grazing animals. Establish salt land pasture species. Excess water with the potential to aggravate salinity problems can be intercepted and re-directed via ground works such as broad surface drains (Figure 7). Subsoil drainage systems can be installed to capture deep drainage water and evaporation basins constructed to store it. Such works generally require formal authorisation from government agencies.
Source: McKenzie (2003)
Figure 7 Surface drains adjacent to a salinised area in Western Australia.
Secondary salinity
A whole-farm approach using a number of strategies is the easiest and least costly way of managing and preventing secondary salinity. Some useful strategies are listed.
Monitor groundwater levels to identify location and extent of high risk areas and implement appropriate management
Once water levels are within two metres of the surface, the capillary rise of saline groundwater causes salts to accumulate at the soil surface and in the root zone
Adopt low recharge farming systems to increase water use efficiency
Use rainwater more efficiently to minimize deep drainage losses. This could be done by growing higher biomass crops, opportunity cropping, permanently fencing off pasture areas, stock exclusion and avoiding long fallows. Replacing long fallow systems with opportunity cropping or cover crops in Queensland should be considered as a means of increasing water use and reducing salinity problems, as well as protecting soil from erosion (case study link).
Manage salt affected areas
Intercept excess water and re-direct via ground works such as broad surface drains and reverse interceptor drains. Install surface, subsurface drainage systems and evaporation basins to capture and store deep drainage water. Evaporation basins should be sealed with impermeable clay or a synthetic liner to minimise leakage.
Protect and manage remnant vegetation. Plant perennial pastures and trees/shrubs in recharge areas. Establish pastures on poor producing land or if a mixed farming system, consider alternate components of rotations such as lucerne. The Land Water & Wool ‘Sustainable Grazing on Saline Land’ program has demonstrated that productive use of saline land is possible.
Improve soil condition to improve drainage and remove subsoil constraints
Identify and remove subsoil constraints so roots are able to access water deep in the profile, increasing water use. Introduce deep rooted perennials (i.e. trees, shrubs, lucerne) or pastures capable of growing throughout the year. Improve drainage where temporary ponding occurs after rainfall. The adoption of zero tillage combined with stubble retention has shown increased leaching of chloride salts and movement of the salt ‘bulge’ deeper in the profile.
Irrigation management
Water has to be applied to flush out the salts that would otherwise accumulate to the point where crop growth is retarded. This is referred to as the ‘leaching fraction’ and varies for a range of water qualities and crop tolerances. Drainage systems with appropriate drainage capacity should be installed.
Introduce appropriate irrigation scheduling and monitoring, and reduce water loss through evaporation from open water ducts and leakage from unlined channels. Assess the quality of irrigation water. In general, water is considered a low salinity risk if EC is below 0.75 dS/m (see Table 3).
Living with salinity
Salinisation greatly reduces options for farming and landscape management. Although it is important not to leave land bare, avoid cropping saline areas. Saltbush has an extensive rooting system (up to 8 m lateral growth and 3.5 m deep) and can thrive under saline conditions (Figure 8). Species such as sea barley grass and samphire have a high to extreme tolerance of salinity and can provide groundcover under very hostile conditions. There is also a grass, Distyclus spicata that has been tried in various saline soils
Source: McKenzie (2002)
Figure 8 Establishment of saltbush significant improves the carrying capacity and profitability of a wool production enterprise.
Other ways to live with salinity include the use of evaporation basins to contain saline water until it evaporates, desalinising water (energy intensive and costly) and the adoption of alternative land uses able to utilise saline water (e.g. aquaculture).