How salinity affects legumes and grasses
Salinity in the top 10 centimetres (cm) varies throughout the season – lowest in July to September, and highest in January to March (. Rainfall in winter flushes salt from the surface, down the soil profile, and evaporation in spring and summer causes salt to cncentrate on the surface. Soil salinity tends to stay more constant below a depth of about 25cm.
Consequences for annual plants
Annual plants on saline soils have a shorter growing season than those on adjacent non-saline soils. High salinities at the start of the growing season delay germination and can kill germinating seedlings of susceptible species. Plants adapted to saltland must either have a high tolerance to salinity during germination or ways to defer germination until later, when surface soil salinities are lower. In spring, high salinities can kill plants prematurely and reduce the time available for seed set.
Consequences for perennial plants
Saline soils increase the stress on perennial plants of summer drought. On saltland, perennial plants must either have mechanisms to cope with high salinity, or have some form of salinity avoidance mechanism, such as summer dormancy (e.g. puccinellia).
In general, plants use the freshest water available to them. Perennials, with their deeper root systems, can extract water from more of the soil profile than annuals. Tall wheatgrass, for example, avoids high surface salinity in summer by accessing less saline water from depth and then uses relatively fresh water closer to the surface during winter.
Know your site
To select the best species for a particular paddock, you need to know:
- your rainfall zone
- EC1:5 measured across the site, at the relevant time and soil depth (see below)
- potential for winter waterlogging
- soil pH
- soil texture.
See Measuring soil salinity for soil salinity classes.
Measuring soil salinity for annual pastures
High salinity on the soil surface during germination stresses self-regenerating annuals in the second and subsequent seasons. We recommend measuring the EC1:5 of the top 10cm over summer–autumn – the period of highest surface salinity – to find suitable soils for annual pastures. This may give an over-estimate of the salinity levels experienced by germinating seeds, but is a much better estimate than measurements taken in winter or early spring.
Measuring soil salinity for perennial pastures
Subsoil salinity in summer is the greatest stress to perennial plants on saltland. Measure soil samples from 25–50cm below the soil surface. This can be done in summer, or whenever the surface is dry.
Assessing waterlogging
Soils of high risk will be sodden for much of the winter, often with prolonged periods of surface water. Soils of moderate risk will remain sodden for up to two weeks after heavy rain, often with surface water visible. Soils of low risk will be free draining.
See Diagnosing waterlogging for more information.
Species selection for saltland
Do not attempt to plant pasture species on extremely saline land (EC1:5 range for loams >295mS/m). Fence these areas and allow natural regeneration of non-pasture species.
There are few salt tolerant legume options for low rainfall regions.
For soils classed as severely saline, messina is the only commercially available legume, and puccinellia and distichlis are the only available grasses.
Use mixtures of species
We recommend using a mixture of appropriate species, to cover the variability of salinity and waterlogging over short distances within paddocks. The best adapted species will colonise those parts of the landscape to which they are suited.
Tables of legume and grass tolerances
- Annual legume options (Table1)
- Temperate annual grass options (Table 2)
- Perennial legume options (Table 3)
- Temperate perennial grass options (Table4)
- Sub-tropical perennial grass options (Table 5)
Establishing salt tolerant pastures
Sowing and fertiliser rates, seeding depth, post-emergent weed and insect control and grazing management will be the same for these species as for establishment on non-saline land. The aim in the year of sowing should be to maximise the seed set of annuals and the ground cover of perennials to set up a long-term pasture.
To improve survival of seedlings on saline sites:
- Control weeds and seed set in the year before establishment.
- Cultivate hard surface soils to increase salt leaching.
- Sow all species, apart from the sub-tropical grasses, soon after early season rains have flushed salt from the soil surface.
- Sow sub-tropical grasses in late-winter or early spring, while the soil surface is still moist and temperatures are beginning to rise.
- Control red legged earth mite.
Inoculate pasture legumes
For effective nodulation of legumes, inoculate seed with the strain of Rhizobium appropriate for the species, just before sowing. This is particularly important on saltland, as background rhizobia levels are likely to be very low or nonexistent, and rhizobia differ in their tolerance to saline conditions.
Weed control
Ideally, weeds should be controlled in the year prior to sowing to prevent seed set. In the planting season, there is often benefit from two knockdown herbicide applications (rotate herbicide groups): the first following an initial weed germination, and the second just prior to sowing. Many weeds (e.g. sea barley grass and ice plant) will have a delayed germination on saline sites (the delay will be longer on more highly affected sites).
Annual legume options (Table 1)
Annual rainfall (mm) | Salinity | Waterlogging risk | Texture | pH (CaCl2) | Suitable species | Suitable species - cultivars1 | Comments |
---|---|---|---|---|---|---|---|
275–325 | Moderate–high | Low | Sandy loams–clay loams | 5.2–8.5 | Burr medic (Medicago polymorpha) | Serena | Less salt tolerant than Scimitar |
275–350 | Moderate | Low | Loams–clays | 5.8–9.0 | Barrel medic (Medicago truncatula) | Caliph | |
300–425 | Moderate–high | Low | Sandy loams–clay loams | 5.2–8.5 | Burr medic (Medicago polymorpha) | Scimitar, Santiago | Scimitar is the best performing burr medic on saltland |
325–500 | Moderate | Low | Loams–clays | 5.8–9.0 | Snail medic (Medicago scutellata) | Sava, Silver, Essex | Seed may be hard to find |
>350 | Moderate-severe | High | Sandy loams-clays | 5.5-9.0 | Messina (Melilotus siculus) | Neptune | Needs salt-tolerant rhizobium |
350–550 | Moderate–high | Low | Sandy loams–clay loams | 5.2–8.5 | Burr medic (Medicago polymorpha) | Cavalier | |
350–550 | Moderate | Low | Sandy loams–clays | 4.8–8.0 | Sphere medic (Medicago sphaerocarpos) | Orion | Little or no commercial seed |
350–550 | Low–moderate | High | Sandy loams–loams | 4.5–8.0 | Balansa clover (Trifolium michelianum) | Frontier | |
425–650 | Low–moderate | High | Loams–clays | 5.0–8.0 | Persian clover (Trifolium resupinatum) | Prolific, Nitro Plus | |
450–700 | Low–moderate | High | Sandy loams–loams | 4.5–8.0 | Balansa clover (Trifolium michelianum) | Paradana | |
>550 | Moderate–high | Low | Loams–clays | 4.5–8.0 | Bokhara clover / White sweetclover (Melilotus albus) | Jota | High coumarin levels can cause haemorrhaging of stock if fed mouldy hay |
>600 | Low–moderate | High | Sandy loams–loams | 4.5–8.0 | Balansa clover (Trifolium michelianum) | Bolta | |
>650 | Low–moderate | High | Loams–clays | 5.0–8.0 | Persian clover (Trifolium resupinatum) | Kyambro | |
>700 | Low–moderate | High | Loams–clays | 5.0–8.0 | Persian clover / Shaftal clover | Many cultivars | One year fodder types |
Temperate annual grass options (Table 2)
Annual rainfall (mm) | Salinity (see Table 1) | Waterlogging risk | Texture | pH (CaCl2) | Suitable species | Suitable species - cultivars1 | Comments |
---|---|---|---|---|---|---|---|
275–650 | Low–moderate | Low | Sands–clays | 5.0–8.0 | Annual ryegrass (Lolium rigidum) | Wimmera, Safeguard | Safeguard has resistance to annual ryegrass toxicity |
>550 | Low–moderate | Low | Loams–clays | 5.0–8.0 | Italian ryegrass (Lolium multiflorum) | Many cultivars |
Perennial legume options (Table 3)
Annual rainfall (mm) | Salinity (see Table 1) | Waterlogging risk | Texture | pH (CaCl2) | Suitable species - common name | Suitable species - cultivars1 | Comments |
---|---|---|---|---|---|---|---|
>400 | Moderate | Low | Sands–clay loams | 5.6–9.0 | Lucerne (Medicago sativa) | Many cultivars | Winter active and highly winter-active cultivars perform best in WA |
>550 | Low–moderate | High | Sandy loams–clays | 5.6–9.0 | Strawberry clover (Trifolium fragiferum) | O’Connors, Palestine |
Temperate perennial grass options (Table 4)
Annual rainfall (mm) | Salinity (see Table 1) | Waterlogging risk | Texture | pH (CaCl2) | Suitable species - common name | Suitable species - cultivars1 | Comments |
---|---|---|---|---|---|---|---|
>400 | High–severe | High | Sands–clays | 5.5–9.0 | Puccinellia (Pucinellia ciliata) | Menemen | Best suited to waterlogged, saline soils, dormant over summer |
>400 | High | Moderate | Sandy loams–clays | 4.5–9.0 | Tall wheat grass Thinopyrum ponticum | Dundas, Tyrell | Tolerates ECe levels >16 dS/m if it can access fresh water at depth, has weed potential in Victoria |
>500 | Low–moderate | Moderate | Sands–clays | 4.3–8.5 | Tall fescue Festuca arundinaceae | Many cultivars | Summer dormant cultivars perform best in WA |
>550 | Low–moderate | Moderate | Loams–clays | 4.5–8.0 | Phalaris Phalaris tuberosa | Many cultivars | Winter active cultivars perform best in WA |
Sub-tropical perennial grass options (Table 5)
Annual rainfall (mm) | Salinity (see Table 1) | Waterlogging risk | Texture | pH (CaCl2) | Suitable species | Suitable species - cultivars1 | Comments |
---|---|---|---|---|---|---|---|
>350 | High-severe | High | Sands–clays | 5.5–8.0 | Distichilis Distichilis spicata | NyPa forage | Only propagated by cuttings |
>400 | Low–moderate | Low | Sands–loams | 5.5–8.0 | Rhodes grass Chloris gayana | Many cultivars | Low frost tolerance, suited to northern and south coastal districts |
>400 | Moderate | Moderate–high | Sands–clays | 3.7–7.0 | Kikuyu Pennisetum clandestinum | Whittet | Performs poorly north of Perth |