Seeding options to stabilise bare, sandy pasture paddocks

Page last updated: Tuesday, 24 August 2021 - 9:30am

An unusual situation has developed in the West Midlands – Coorow district where there are a number of bare, sandy paddocks which have little or no groundcover coming into spring. This is unusual in any year, but especially in a year where there has been excellent winter rainfall. This issue is confined to annual pastures on sandy soils, as most cropping and perennial pasture paddocks are well covered and there are annual pastures on the gravelly soils.

This is an unusual, and difficult situation. It is imperative that producers get cover on these bare paddocks or they will continue to erode right through summer.

A series of events have come together to cause this situation and while the specific circumstances vary from paddock to paddock, they are most likely due to a combination of factors.

The annual pasture seed bank has been drastically reduced due to:

  • low pasture seed banks in paddocks coming out of crop.
  • last spring a combination of grasshoppers together with a prolonged dry spell in September would have drastically reduced the seed-set of annual pastures.
  • good rains in February-March over the last two years have resulted in false breaks.
  • grasshoppers again this season have been prolific in some areas, especially early in the growing season.
  • loss of topsoil from wind erosion – paddocks with inadequate groundcover over 20/21 summer were hit with the strong winds associated with passage of Cyclone Seroja in April, followed soon after by other strong wind events.

Many producers realised they had a serious issue back in July, so started sowing to get groundcover and protect their paddocks from wind erosion with whatever seed was on hand. However, there are still many paddocks with inadequate cover, so what can be done in the short-term?

Two broad groups of affected paddocks

1. Paddocks where most of the paddock is affected:

  • exclude stock
  • reseed for cover, otherwise susceptible to wind erosion until May-June 2022
  • need to develop a longer-term plan for these paddocks (potentially permanent pasture with perennial species).

2. Paddocks where the valleys are badly affected, while some areas of the paddock have adequate cover.

  • Fencing to exclude stock from bare areas while still allowing some grazing on areas with good pasture cover (e.g. subclover on gravelly soils).
  • Alternatively, no grazing across entire paddock.
  • Reseed the bare areas for cover.

The key issues are what are the options for this year and moving into 2022 these paddocks will need to be carefully managed.

What can be done about the situation now?

In most situations non-wetting soils will not be an issue and there should be plenty of subsoil moisture. If planning to re-seed, it will pay to keep a close eye on the rainfall outlook and sow into moist soil or when rainfall is likely.

Three short-term options to get groundcover, none are perfect, but given the circumstances these are the better options:

  1. Temperate (C3) annual grasses

There is a small window up to about mid-September when producers could sow a mix of annual grasses like cereal rye, Shirohie millet and feed barley. The primary objective here is to get groundcover with any grazing a bonus if conditions allow.

For soil stabilisation sow a mixture @ 20kg/ha.

  1. Warm season (C4) annual grasses

After mid-September, the preferred option would be to sow warm season (C4) annual grasses, like hybrid sorghum, Sudan grass and pearl millet.

These grasses require warm soil temperatures for good germination:

  • Hybrid sorghum minimum soil temperature 16°C, optimum temp. >18°C
  • Pearl millet minimum soil temperature 18°C, optimum temp. >20°C

These grasses are fast growing when conditions are favourable – warm temperatures + soil moisture + fertility.

Normally sown in spring with a full moisture profile. Once again, limited grazing value without risking wind erosion. It is important for livestock producers to note that hybrid sorghum has a risk of prussic acid poisoning (particularly small, stressed crops), so if planning to graze, it would be safer to sow pearl millet (nil risk) or Sudan grass (low risk).

For more information on growing Summer crops refer to: Guide to growing summer grain & forages in the south coast region, Western Australia.

For soil stabilisation sow pearl millet @ 5kg/ha and forage sorghum @ 5-10kg/ha.

  1. Sub-tropical perennial grasses

These sandy soils are well suited to sub-tropical warm season grasses – they provide perennial groundcover, valuable out-of-season green feed and with good management will be a productive, long-term pasture. The sowing window is from mid-August to early September in this region.

Observations from the affected areas this year show a stark contrast between annual pasture paddocks with little cover compared with perennial pastures on adjacent paddocks with excellent groundcover.

We normally advise against sowing sub-tropical grasses into bare paddocks with little or no root material to hold the soil together as there is a high risk of failed or patchy establishment. This is because substantial sand in-fill into furrows greatly increases the effective depth of seeding. Subtropical grasses like Rhodes grass are very sensitive to seeding depth (ideal sowing depth 0-5mm) which adversely affects emergence resulting in patchy or failed establishment. Sand-blasting of seedlings can also occur.  However, a local contract seeder has developed an innovative method, albeit experimental to reduce the risk of wind erosion during the establishment phase by broadcasting a mix of C3 annual grasses (feed barley, Shirohie millet, cereal rye) in front of a seeder modified to sow sub-tropical grasses. Alternatively, sow the perennial and annual grasses in separate seeding rows to reduce competition to the perennial grasses which are comparatively slow to establish.

Further information refer to: Sub-tropical grass establishment or download Bulletin 4840 Sub-tropical grass establishment Guide.

With any re-seeding, growers need to regularly monitor for grasshoppers and control as necessary.

Careful planning for 2022 season

With annual pasture paddocks in the West Midlands region – producers will need to carefully plan ahead for the 2022 season. Large areas with an inadequate annual pasture seed bank will require some level of re-seeding. In paddocks with a low or minimal cover this may also involve sowing a cover crop to protect the pasture while it establishes.

Also, a reminder to farmers grazing stubbles and dry pasture over summer to maintain at least 50% groundcover right through to the end of autumn 2022 to minimise the risk of wind erosion.

Contact information

Geoff Moore
+61 (0)8 9368 3293

Author

Geoff Moore