Puccinellia (Puccinellia ciliata) for dryland salinity management

Description

The Puccinellia genus has dozens of species from northern and southern hemispheres. There are 3 species native to Western Australia (P. longior [1], P. stricta [2] and P. vassica [3]) and 2 introduced species (P. ciliata [4] and P. gigantea [5]). All of the information below is about P. ciliata, which is widely planted on saline land in Western Australia.

Puccinellia is a compact perennial grass, forming tussocks up to 40cm high and wide. Its leaves are long and thin, with the growing points embedded in the base of the plant, which protects the growing points from grazing (Figure 1).

[6]

Figure 1 Puccinellia (Puccinellia ciliata) photographs from SALTdeck

The plants hay-off in December and remain dormant over summer (Figure 2). They shoot vigorously after the opening rains of autumn. The plants are monoecious. Flowers are formed in September and the seed is ripe by December.

Figure 2 Puccinellia tussocks are green in winter (a) and are dormant with dry tops over summer (b)

[7] (a) Puccinellia tussock green during the winter growing season

[8] (b) Puccinellia tussock dry over the summer dormancy period.

Benefits

Production

Puccinellia is highly palatable and productive grass with good tolerance of salinity and waterlogging. It is not a halophyte [9], and has a low salt concentration in the leaves.

The plants grow from mid autumn to spring and mature (hay off) in November–December, remaining dormant over summer to early autumn. It has its highest grazing value in winter and spring while green and before flowering. Nutritive value declines as the plant flowers, matures and senesces, and further declines through summer and autumn even though it is still palatable.

It changes from a high-quality, highly digestible feed capable of supporting high animal liveweight gains in spring to less than a maintenance ration in late summer/autumn.

Mature stands can be grazed after the opening rains (when they rapidly produce green feed) and/or more commonly as dry feed in late summer-autumn, although at this stage some supplementation will be needed unless weight loss in the animals is acceptable. Leaving the feed standing over summer shades the soil, reducing the concentration of salts at the soil surface through evaporation.

Puccinellia provides good feed for sheep on saltland, in most instances providing a pasture sward free of problem grass seeds. Some landholders also successfully harvest puccinellia seed in summer to autumn either for sale or their own on-farm use.

Water use

Puccinellia pastures use almost no water over the summer period, when they are dormant – they senesce after flowering and seed set in spring, and do not resume growth until the autumn break. If water use is one of the objectives behind establishing a saltland pasture, then puccinellia is not a suitable option. Unlike puccinellia, tall wheatgrass will use water in summer, however for this option to work, the site needs to be less waterlogged and less saline than the upper limit for puccinellia.

Amenity and environmental

Under suitable conditions (high salinity and waterlogging), puccinellia will transform the visual amenity, from bare scalded areas into productive pastures with a high degree of groundcover.

Puccinellia-based pastures can significantly slow the build up of salts in the surface soil. The dry puccinellia-based pasture shades the soil in summer, and reduces evaporation from the soil surface, thereby reducing the concentration of salts at the soil surface. This reduces salt movement off-site.

Puccinellia-based pastures have a biodiversity value intermediate between bare salt scalds and remnant native vegetation, as measured by Landscape Functional Analysis.

Economics

The Sustainable Grazing of Saline Lands program confirmed the suitability and productivity of puccinellia-based pastures for the moderately to highly saline, waterlogging-prone areas of the Upper South East of SA. These benefits are due to a combination of the increased pasture growth and improved nutritive value relative to the previous sea barleygrass-dominant pasture base.

Sowing puccinellia pastures in that area increased the carrying capacity of saltland from 2.4DSE/ha to 6.7DSE/ha.

A multi-year gross margin model estimated that puccinellia pastures and an increased stocking rate resulted in an $86/ha improvement in wool enterprise gross margin per year.

At the research sites, the investment in pasture improvement paid for itself within two years. With an expected lifespan of at least 10 years, the annual rate of return on capital invested in pasture renovation was calculated at 47% per year.

Puccinellia-based pastures are probably the most widely adopted saltland pasture system in Australia – there are at least 200 000ha of puccinellia-based pastures in the Upper South East of SA.

Suitable sites for puccinellia pastures

[10]

Figure 3 Most likely situations for puccinellia pastures

Common indicator species

Puccinellia is highly salt- and waterlogging-tolerant and is relatively non-competitive outside that zone.

[11]

Figure 4 Relative rankings of different saltland pasture species in the salinity-waterlogging matrix

Therefore, the common indicators for the puccinellia zone are sea barleygrass [12], curly ryegrass [13], beardgrass [14] and samphire [15]. There may also be patchy scalding across a site suitable for puccinellia.

Soil salinity

Puccinellia can withstand salinity in the surface soil (0–10 cm) in summer up to 50dS/m (measured as ECe). Often, puccinellia sites are highly waterlogged over winter, and during that time, surface soil salinities can be far lower. It is this lower winter salinity that makes Neptune messina [16] a potential partner in puccinellia-based pastures.

High surface soil salinity during germination is the main cause of decline in balansa clover with time on saltland. Given this and the importance of balansa in the feed mix, we suggest that the puccinellia/balansa system be focused onto waterlogged saltland with ECe values less than 16dS/m.

Soil acidity

Puccinellia is particularly suited to alkaline or highly alkaline soils, and will tolerate a fairly wide range of soil pH.

Rainfall

Puccinellia is only recommended in the higher rainfall zones (more than 400mm) across southern Australia.

Waterlogging and surface water management

Puccinellia is tolerant to prolonged periods of winter–spring inundation (more than three months) as long as the plants are ‘tall’ enough to stay at least partially out of the water. Some landholders report that puccinellia actually benefits from extended flooding, provided plants are not totally submerged and surface water does not stagnate. It is substantially more waterlogging-tolerant than saltbush, and more salt-tolerant under waterlogged conditions than tall wheatgrass.

Puccinellia has three important adaptive traits that enable it to grow in saline waterlogged conditions:

• formation of aerenchyma – hollow channels in the roots that enable oxygen to diffuse down the inside of the root and therefore prevent oxygen starvation in the roots
• formation of a barrier in the roots that reduces the rate at which oxygen leaks out of the aerenchyma into the surrounding soil
• arrangement of root cells in a way that maximises the gas-filled spaces between the cells.

Establishing puccinellia pastures

Choosing the right species and varieties

Decide whether to make puccinellia the only species, or to include a legume with the puccinellia, or to sow puccinellia as one component of a shot-gun mix. There is currently only Menemen or Restora Sweet Grass puccinellia from which to choose – but in fact they are essentially the same plant.

Oversowing puccinellia with a legume such as balansa clover or burr medic has been shown to be very successful but persistence of the clover can be a real limitation depending on salinity, waterlogging and management of the puccinellia pasture.

Control pests

Red-legged earth mite (RLEM) can severely damage puccinellia seedlings, so monitoring and control during establishment is important. We recommend that you use the Timerite® [17] program for managing RLEM.

Prepare the site

• Control surface water to prevent excessive waterlogging. Shallow drains [18] can remove ponding water on the site, and grade banks [19] and diversion banks above the site can prevent water accumulating on the site.
• Fence the area to manage livestock grazing. Temporary electric fencing is an effective option around saltland. Exclude stock during establishment.

Cultivation

Cultivate most soils in early autumn (March/April) leaving a ridged or rough seedbed. Sandy soils in low rainfall areas should not be cultivated until after the break of season, due to the risk of wind erosion),

Leave a rough seedbed in heavier soils or high salinities because it:

• allows opening rains to leach accumulated salts out of the soil surface
• prevents opening rains flattening the soil surface and creating a surface seal which impedes plant emergence
• reduces the incidence of sand blasting which can destroy young establishing puccinellia plants
• provides a buffer against waterlogging and salt on the slightly higher ground
• creates a range of niches in which surface seed can lodge.

On sandier or moderately saline ground a high level of ridging or roughness is less crucial, although it can be of benefit on non-wetting sands (to .

Weed control

Weeds must be controlled for successful establishment of puccinellia-based pastures. Weeds, particularly sea barleygrass and curly ryegrass, can also become a problem in established stands of puccinellia.

Spray-topping has some success in controlling sea barleygrass and curly ryegrass – apply the herbicides from early tillering to head formation, and at the median soft dough stage for sea barleygrass.

If the puccinellia pasture is not sufficiently robust to fill bare gaps, there is a risk that curly ryegrass could fill the spaces. Curly ryegrass is a highly salt-tolerant plant that is very competitive on saline sites, but has very low productive value.

Sea barleygrass is a major indicator species for where puccinellia will grow well, and can tolerate the high levels of waterlogging often associated with suitable puccinellia sites. Where puccinellia is to be established, sea barleygrass must be controlled, otherwise it will out-compete the small and relatively slow-growing puccinellia seedlings.

For controlling aggressive weeds such as sea barleygrass, spray weeds twice. A spray-top in the spring prior to the year of seeding is recommended to reduce the weed seedbank in the autumn when puccinellia will be sown. In addition, a knockdown herbicide at the break of the season to remove the first germination of sea barleygrass (and any other weeds) will assist in reducing the competition faced by the emerging puccinellia.

Other weed control options include burning and cultivation, or a combination of chemical and mechanical methods. The bottom line is that without thorough weed control, successful establishment of a puccinellia pasture is unlikely.

Sowing

Seed should be dropped onto the soil surface, or sown at a very shallow depth. This can be done with a small seeds box or the seed can be mixed with superphosphate (up to 100kg/ha of superphosphate) just before seeding and sown through the fertiliser box.

Avoid harrowing, particularly on heavy soils or high salinity sites. Trial work has shown up to a threefold depression in dry matter production in the first year of establishment if the seed is covered using trailing harrows.

On clayey soils – leave the soil rough to assist in leaching of salt.

On sandier soils – a light rolling post-seeding is beneficial for germination and establishment, through better seed-soil contact and moisture retention, but should be avoided where prolonged waterlogging is likely.

Seek local advice to see what has worked in your area.

Seeding rate

Sow at 4 to 10kg/ha. Use the higher rate when sown alone, particularly where salinity is more severe, or where an influx of weeds is likely. As a general rule, denser pastures will yield higher productivity and so the higher seeding rates can produce a stronger stand.

In a pasture mix, 4kg/ha of puccinellia seed is a more usual rate. A small but significant percentage of seed may not germinate but can still be viable. This is classified as ‘fresh ungerminated seed’ and requires a period of extended flooding to germinate.

Some landholders consider fresh ungerminated seed an essential and valuable component of the seed bank, because it survives false breaks and can germinate after extended flooding.

Fertiliser at establishment

Phosphorus (P)

Adequate phosphorus levels and periodic applications of nitrogen will promote the competitive ability of  puccinellia against weeds.

Add phosphorus fertiliser if P test levels are below 12mg/kg (Colwell P). Phosphorus requirements will be higher (>20 mg/kg Colwell P) if balansa clover is in the mix.

Nitrogen

Nitrogen can be applied at seeding time, but higher applications may largely dissipate before the nitrogen can be used by the slow-germinating puccinellia. Plant emergence can take as long as two months on bare saline scalds. However, on more fertile sites nitrogen can boost growth and provide the advantage of earlier grazing.

On suitable sites, companion legumes will reduce the requirement for nitrogen fertiliser.

Whenever nitrogen is applied, the timing and risk of waterlogging are critical to success. Nitrogen may be lost through the bacterially-mediated process of denitrification if waterlogging occurs soon after application. MAP or DAP at seeding can apply nitrogen and phosphorus at the same time.

Timing of sowing

Where sea barleygrass is present, it is essential to wait for germination of the weed seeds then spray, then sow the puccinellia. Sow puccinellia as soon as possib le after the weeds are controlled.

Dry sowing of puccinellia is possible if weeds have been controlled in the previous two springs. Dry sowing avoids the problem of getting bogged in waterlogged saline soil.

Opening rains will usually leach some of the accumulated salt out of the soil surface making the site more suitable for puccinellia seedlings. Timeliness is critical and can make a big difference to the success of pasture establishment.

In higher rainfall areas (above 475mm) sowing in late winter to early spring has given promising results. Success at this time of year relies on good or spring rainfall, to allow the germinating puccinellia sufficient time to reach sufficient size to survive the hostile summer conditions.

In low rainfall areas, if opening rains have not come by early June, delay sowing until the next year.

Management

Defer grazing after initial seeding

Puccinellia seedlings are small, relatively slow-growing, highly palatable and susceptible to being pulled out by sheep. Therefore, it is best not set stock until the end of the second growth season after establishment (about 18 months), to allow plants to properly establish. Careful strategic grazing may be possible if puccinellia establishes rapidly.

Stands of puccinellia will thicken in subsequent years if allowed to set further seed over the first summer. Where soil fertility is high and where higher seeding rates are used and/or pastures thicken up (and reseeding in the second year is less critical), early light grazing may be an option.

Grazing

Grazing control is essential, because establishing puccinellia plants are highly palatable, selectively grazed, and are easily pulled out by sheep.

Grazing puccinellia to fill the late summer-autumn feed gap produces the highest economic returns, especially if that reduces the need to buy expensive supplementary feed. Even though the dry puccinellia at this time has lower digestible energy, it still compares favourably with other dry pasture feeds.

Puccinellia plants shoot vigorously following the opening rains, and the feed quality is highest through winter to late spring. However, waterlogging and inundation are features of sites that suit puccinellia. Grazing on waterlogged, saline land can damage soil structure and lead to animal health problems. Seek local advice on how best to manage severely waterlogged sites..

Graze winter flooded sites sparingly early in the season, to ensure plant shoots can remain above water. On heavily flooded sites, defer grazing until after spring, and have a feed budget and grazing plan for the full property.

Puccinellia stands commonly support 5DSE/ha. With appropriate management and fertiliser application (including nitrogen), dry matter yields can be doubled and stocking rates of 6–8DSE/ha supported. At these stocking rates liveweight gains of more than 120kg/ha and clean fleece weights of more than 20kg/ha can be achieved.

Do not set stock until the end of the second growing season after establishment (about 18 months) to allow plants to properly establish, particularly if a lower seeding rate has been used. While it is preferable not to graze during this establishment phase, careful strategic grazing may be possible. Established puccinellia will tolerate hard grazing, but to maintain a vigorous stand, plants should be allowed to set seed at least once every two to three years.

Unlike some saltland grasses (e.g. sea barleygrass), puccinellia seed is not damaging to animals and does not embed itself in wool, so puccinellia paddocks can be used as a weed-seed free zone during the ‘grass seed season’ for sheep meat and wool production.

This strategy relies on the puccinellia pasture being well maintained and therefore sufficiently vigorous to prevent weed (especially sea barleygrass) invasion.

Animal nutrition issues

The grazing value of puccinellia depends on its stage of growth:

• Green leaves in winter and spring have high crude protein content (15–25%) and high digestibility (60–75%).
• When dry in late summer and early autumn puccinellia remains palatable but has low nutritional value (crude protein less than 5%, digestibility less than 50%).

Mineral analysis has shown that several important nutrients (particularly phosphorus) and trace elements (particularly copper) decline sharply over summer-autumn.

We recommend tests of the various feeds available on the farm, and matching the feed and supplements to the class of animal. See Supplementary feeding and feed budgeting for sheep [20] for more information.

Productivity increases from fertilisers and companion legumes

Puccinellia responds well to increased nutrition: production will increase and nutritional value will improve.

Maintain phosphorus level above 12mg/kg (Colwell P).

Nitrogen (N) can be supplied as fertiliser or from legumes in the stand. The nutritive value of the green and dry feed is significantly boosted with adequate N.

See pasture the legumes and grasses for saline land [21] to select legumes to suit different sites. Neptune messina [16] is the only legume that has high tolerance of salinity and waterlogging.

Additional nitrogen will:

• increase productivity from the puccinellia through the promotion of tillering and improved growth per tiller
• improve long-term survival of puccinellia –  the plants are stronger, more vigorous and able to tolerate higher levels of salt, flooding or waterlogging
• increase development of dormant tiller buds – these become tillers in the following year and this ‘sets’ the plant up for higher productivity
• increase feed quality – digestibility is often increased, but there is little effect on protein unless nitrogen has been applied above the growth demand of the plant
• increase seed production – this is a major consideration if the pasture it to be harvested for seed, or if thickening of the sward is needed.

Applying nitrogen fertiliser in the late autumn – early winter period appears to give the best response economically, particularly for early winter feed. In one trial, 25kg N/ha (50kg urea/ha) applied after the break of season (while conditions were still relatively warm) gave an additional 150kg DM/ha in two weeks and 300kg DM/ha in four weeks. This was a 50% increase in pasture production over the period.

Mid-winter applications may be an appropriate strategy for drier areas (<400mm) that are unlikely to become excessively waterlogged over winter and therefore risk heavy losses of nitrogen. In colder/wetter areas, this late application is rarely effective because soil temperatures are too low, and waterlogging inhibits nitrogen effectiveness.

Rates of nitrogen application

Optimal rates are related to rainfall and intended use of the pasture (Table 1). Higher rates are economical if the pasture is used for seed production.

Table 1 is a only a guide, as site and seasonal conditions influence fertiliser responses and make it difficult to provide generalised advice.

The form of nitrogen applied (urea, ammonium nitrate, sulphate of ammonia, etc) appears to have little effect on overall response. Therefore the cheapest form, urea, is recommended. To avoid losses by volatilisation, urea should be applied to damp soil or just prior to rain. If this is not practical, apply urea late in the afternoon.

Rising fertiliser costs should also be factored in when making assessments of cost-effective application rates.

Renovation

Established pastures that have large bare areas can be roughly cultivated using an implement such as a cultivator with every second tine removed. This will provide suitable areas to trap seed and allow germination, without killing the existing stand.

Cultivate only where significant bare areas are present. A single-tyned ripper can also be used, especially along the edge of existing stands. Early autumn or late spring is the best time to cultivate. Restricting grazing to let puccinellia seed mature and drop, is another way to let the stand thicken up.

Resources

Barrett-Lennard, EG, Bathgate, AD and Malcolm, CV (2003) Saltland Pastures in Australia, a practical guide. WA Government. Dept. of Agriculture and Food. viewed 5 May 2020, https://www.researchgate.net/publication/318011520_Saltland_Pastures_complete_book [22]

Edwards, NJ, Hocking Edwards, JE, Sanders, D and Revell, DK, 2002, Sheep production on puccinellia-based pastures in South Australia, viewed 11 November 2019, http://livestocklibrary.com.au/handle/1234/9104 [23]