Tall wheat grass in saline soils
Originating from the Balkans, Asia minor and southern Russia, tall wheat grass (Thinopyrum ponticum) is a drought tolerant, summer active, tussock-forming perennial that grows to a height of 2 metres.
When used with companion legumes, it is invaluable for rehabilitating and improving agricultural productivity in land affected by secondary salinity (human induced salinity).
Typical of all introduced plants, managing wheat grass must be aimed at confining it to where it is sown. The easiest and most effective method to achieve this is to not allow it to set seed over summer.
Well managed tall wheat grass pastures can:
- increase stocking rates from 0.5DSE per hectare up to 8DSE per hectare
- provide palatable green feed over summer
- use soil moisture and dry the profile out over summer into autumn
- leach salt stored in the soil down the profile after summer rainfall
- reduce salt loads entering waterways
- reduce soil erosion and water velocity over the soil
It persists in winter waterlogged soils that dry out in summer and grows equally well in acid and alkaline soil. It does not persist in soils that are waterlogged over spring and into summer. Under these conditions, Lotus pedunculatus may be a better option.
ECe is the electrolyte conductivity measured on soil paste extracted from a saturated soil sample. The units used here are deciSiemen per metre.
The electrolyte conductivity may also be measured on a 1:5 soil:water sample, nominated as EC1:5. This alternative will give lower EC values.
Tall wheat grass grows particularly well in moderately saline areas that grow sea barley grass and buck's horn plantain with an ECe in top 10cm of soil of less than 5 dS per metre. It also establishes in areas where salinity levels are far more severe (ECe in top 10cm of up to 40 dS/ per metre).
Where to sow tall wheat grass
To prevent tall wheat grass spreading into unintended areas where it can compete with native vegetation, several environmental best management practices need to be considered.
Tall wheat grass and companion legumes:
- should only be sown in man induced saline areas (secondary salinity)
- must not be sown in naturally salt affected wetlands (primary salinity)
- must not be allowed to set seed over summer
- should not be sown next to or in environmentally sensitive areas (riparian zones, areas of primary salinity, coastal and inland wetlands, breeding or feeding habitats for native fauna, areas containing rare and threatened flora)
- should be sown where the aim is to establish and manage it as a viable grazing pasture
- must not be sown if the intention is only for ground cover and not to be grazed
Establishing tall wheat grass
Tall wheat grass is an improved pasture variety and must be established along the same lines as other types of improved pasture.
The affected area must be fenced out and managed as a separate paddock.
A soil test should be conducted to determine the fertiliser requirements and the ECe reading in the top 10cm of soil. In most saline areas, phosphorous and nitrogen are limiting and sulphur is not required. For tall wheat grass to establish quickly in autumn, apply 100kg per hectare of a nitrogen based fertiliser such as M.A.P. at the time of sowing.
The ECe reading or salinity level of the soil will affect the sowing rate and pasture companion species. The higher the ECe, the higher the sowing rate for tall wheat grass and the fewer pasture companion species available.
Sites with low ECe readings can be sown with a pasture mix of:
- 7kg per hectare tall wheat grass
- 15kg per hectare tall fescue (Festuca arundinacea)
- 1kg per hectare strawberry clover (Trifolium fragiferum)
- 0.5 kg per hectare balansa clover (Trifolium michelianum).
Sites with moderate to high ECe readings can be sown with:
- 10 to 15kg per hectare tall wheat grass,
- 6kg per hectare puccinellia
- 2kg per hectare strawberry clover
- 1kg per hectare balansa clover
Another companion species suited to saline areas is Persian clover (Trifolium resupinatum).
It is essential tall wheat grass seed is fresh. Germination percentages decline rapidly if the seed is more than 2 years old.
While waiting for the results of the soil test, spraytop the pasture in spring and graze over summer until it is bare by the end of March.
Scarifying beyond the A1-A2 horizon after rain creates a roughened soil surface for seed to settle into and establish. In some situations, scarifying may not be an option if the site Is on a steep gradient or along a flowing drainage line. Under these circumstances, consult your local adviser for on-site advice.
After scarifying, wait for the opening rains and weeds to germinate before doing a complete knockdown. Weed control before sowing is critical especially as tall wheat grass is an inherently weak seedling.
Direct drill the pasture in with Baker Points or equivalent sowing implements in April or May after the opening rains. If the area is likely to get too wet after the opening rains, sow the seed in dry.
As most discharge sites are too wet during spring to get machinery on to, autumn is the preferred sowing time. Likewise, if there is an early finish to the season, the newly sown tall wheat grass plants may struggle to germinate and grow in an environment where surface soil salinity increases in summer.
In an area where the ECe reading is moderate to severe, it may be necessary to cover the ground with a mulch of old hay or slashed tall wheat grass after the site has been scarified. This provides an initial vegetative cover which will help conserve soil moisture and reduce the salinity concentration in the top 10cm of soil through lower evaporation. It will also add organic matter to the soil which will help improve the soil structure.
Tall wheat grass will germinate from seed. It starts to run up to seedhead in summer and seed drop will occur in late summer or autumn. Grazing is essential to prevent seed set and spread to unintended areas.
First year of sowing
Sites sown to tall wheat grass in low to moderate ECe saline areas can be lightly grazed in early September before balansa starts to flower.
This will only occur if the tall wheat grass plants are firmly anchored to the ground and the discharge site is not waterlogged.
This can be tested by pulling at the base of the plant with the thumb and forefinger. If the plant is easily removed, do not graze until after balansa seed set is complete by mid to late December.
At the first sign of balansa flowering, remove the stock. Once balansa seed set is complete, crash graze the pasture down to a uniform stubble of 10cm. This will:
- remove excess growth
- help control weeds
- encourage better leaf growth over summer
- make the grazing management over summer easier
After the initial crash graze, lightly graze the pasture over summer and autumn to maintain a height of approximately 10cm to encourage strong root development and water use. Give the pasture one last heavy graze at the autumn break to remove any excess trash. This provides a favourable environment for balansa to regenerate.
Over winter, do not graze the pasture if the site is waterlogged. If the site is not waterlogged or pugged by stock, graze it to utilise the balansa clover.
Sites with moderate to severe ECe readings may need to be spelled from grazing for up to 2 years after sowing. This will depend on how successful the establishment was, how severely the site is scalded and how well the plants are growing.
Second year after sowing
Top-dress the pasture in autumn with appropriate phosphorus based fertiliser in each of the ensuing years to maintain a highly productive pasture. Moderate levels of salinity restrict legume growth and good responses can be expected from 50kg nitrogen per hectare as urea in late autumn or early spring.
In the following spring, (18 months after sowing) graze the pasture hard to make use of the balansa clover. At the first sign of balansa flowering, shut the paddock up and allow the balansa to set seed. After balansa seed set is complete, crash graze the pasture hard to remove any excess growth and tall wheat grass stems.
To prevent the pasture from going clumpy and rank, graze it similarly to a well-managed phalaris pasture. The pasture should be no more than 10cm high over the summer months. If stock appears to be selectively grazing areas bare, crash graze it to a uniform height — tall wheat grass handles hard grazing well. The pasture can be grazed through summer and into autumn until the paddock becomes too wet for stock to walk over.
To encourage balansa regeneration, give the pasture one last heavy graze at the autumn break to remove any excess growth.
Maintaining this simple but highly effective grazing pattern will result in a pasture that is easy to manage and highly productive. When managed correctly, tall wheat grass has the potential to cut high quality silage or hay. It is also a great fodder reserve in summer and very effective in stabilising and rehabilitating soil in fragile, saline areas.
Widely used in Australia. It has many varied agronomic traits.
A newer cultivar Dundas was developed from Tyrrell. It was selected to enhance leafiness and quality.