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Published: 19 Aug 2021

Grass and legume-mixed pastures sown in autumn can often see the grass component out-compete the legumes during the critical establishment phase, with the result being a long-term grass-dominant pasture.

With spring not far away, Research Fellow in Pasture and Forage Science with TIA, Rowan Smith says Tasmanian farmers have traditionally sown permanent pastures in autumn – often as a grass/legume mix.

However, Dr Smith says that experience in Tasmania is indicating that if farmers in the dryer and cooler parts of the state want to maximise the long-term productivity benefits from perennial legumes in their pastures, they should consider sowing these grass/perennial legume mixes in early spring (August/September).

Grass and legume-mixed pastures sown in autumn can often see the grass component out-compete the legumes during the critical establishment phase, with the result being a long-term grass-dominant pasture.

Failure to get legumes established can reduce overall productivity, resilience and missed opportunity to realise other benefits legumes can provide in a mixed sward.

The reason for poor establishment of legumes when sown in the autumn is that they are less vigorous than grasses during early establishment under cold autumn/winter conditions.

Long-lived deep-rooted perennial legumes prioritise energy into the development of roots systems than leaf growth during establishment than other legumes.

This can result in being shaded out and not fully establishing during this critical period.

Dr Smith said this is particularly an issue in the Midlands region of Tasmania.

“Given that a well-managed grass/legume pasture should last for 15-20 years, this alternative sowing strategy could have significant long-term benefits for producers – particularly in the Midlands,” Dr Rowan Smith said.

However, producers with sandy/ light free-draining soils may need to stick with autumn sowings as they can be more susceptible to drying out quickly in late spring.

One strategy that could be considered is to establish a fodder crop in the autumn to provide early autumn/winter feed and then direct drill a grass/legume mix in the late winter/early spring.

This means the area, which has been sown down, is only being taken out of production during spring when pasture/feed is likely to be more abundant.

Spring’s warming temperatures, increasing day length, and existing soil moisture can favour quick root development and following herbage growth.

“Producers with access to irrigation could also consider sowing in late summer/early autumn, (February/March), which would still give time for the legume component while soil temperatures are still warm and compete with the grass component,” Dr Smith said.

Once the root systems are established these pastures will benefit from regular light grazing to keep them open and allow the grass/legume components to compete with each-other.

A series of experiments are currently underway in the Midlands focusing on advantaging legumes during establishment.

“It’s very difficult for legumes to persist long-term if they don’t establish to begin with,” Dr Smith said.  “We are trialling a number of sowing techniques to spatially or temporally separate the grass and legume at sowing to reduce competition.”

TIA is also undertaking research into strip sowing various perennial legumes into existing pastures, which is showing potential to improve the legume content without taking the risk of full pasture renovation.

Reducing the risk of pasture establishment failure is particularly relevant in dryland areas such as the Midlands, East Coast and Central Highlands.

Workshops and field days will be held in the Midlands and the North-West Coast regions in November this year.