New medics to revive Mallee rotations

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Pasture Legumes

Well-nodulated, medic-dominant pastures are known to provide a disease break, high-quality stock feed and biologically fixed nitrogen. Yet for many Mallee growers, medics have fallen from favour due to poor performance.

Plant breeders at the South Australian Research and Development Institute (SARDI) have some new material that could provide a valuable break crop for low-rainfall mixed farmers and continuous croppers.

A picture of two men crouching in a field

(Above) Jake Howie (left) and Ross Ballard, SARDI, are delighted with the initial field performance of new strand medics with multiple beneficial traits

A photo of a green field with a sign.

A new strand medic with multiple beneficial traits, including tolerance of sulfonylurea herbicide residues, aphid resistance and resistance to powdery mildew, is performing well in the Mallee.

PHOTOS: Emma Leonard

The cultivars HeraldPBR logo and AngelPBR logo have been the benchmark strand medics for lighter soil types within this zone. Now Jake Howie and colleagues at SARDI have shortlisted a small group of strand medics that produce up to 30 per cent more dry matter and seed than these benchmark cultivars.

“These hybrids have better early-season dry matter production, possibly due to their larger seed size,” says Jake Howie, who, with colleagues Ross Ballard and David Peck, has developed these lines as part of a project supported by the SA Grain Industry Trust and with past assistance from the GRDC.

A key feature of each of the lines is that they have been bred with multiple beneficial traits. As well as tolerance of sulfonylurea herbicide residues and aphid resistance, they also have resistance to powdery mildew. Together with the larger seed size these factors combine to boost production.

“These are the first strand medics with powdery mildew resistance. While their initial performance has been exceptional, we need to do further testing to make sure their resistance is robust to different mildew strains that may occur in the different areas the medics will be grown.”

Annual medics in general have been shown to boost production across the rotation.

Two field experiments run by CSIRO at Karoonda in the SA Mallee have found that medics significantly boosted the yield of the following wheat crop.

A naturally regenerating (unimproved) medic-based pasture grown in 2010 increased 2011 wheat yield by an average of 0.61 tonnes per hectare and 0.93t/ha at the two trials. There was also a residual benefit to the 2011 wheat crop from pasture grown in 2009, of 0.36t/h and 0.61t/ha.

“One can only speculate what an improved pasture with better nutrition, weed control, higher plant density and greater biomass production might achieve in these low-rainfall districts,” Mr Howie says.

Inoculation

As a legume, medics require the correct rhizobia to be present if they are to nodulate and fix atmospheric nitrogen. One of the surprising findings in these trials was the degree of benefit gained by inoculation of medics on some Mallee soils.

“Due to a long history of medic production in this region we did not expect that inoculation would reap significant benefits, but we were wrong,” says rhizobia specialist Mr Ballard.

Inoculation trials were started following anecdotal reports of poor nodulation of medic pastures being grown in the Mallee. Evidence of improved nodulation and production was seen at three trial sites in the SA Mallee in 2011.

In 2012, rhizobia were watered on to the plots soon after plant germination. In August, rhizobia nodules were counted on the roots of 15 plants sampled from each plot. The mean nodulation of the eight medic lines increased by nearly nine-fold where plants were inoculated with rhizobia.

In addition, inoculation increased medic shoot growth by 45 per cent. The research group is interested to explore if the addition of inoculant to existing pasture paddocks with a poor history of nodulation could boost their nitrogen fixation and production.

The factors causing poor medic nodulation on soils that have a long history of medic production still need to be established. In the meantime, the researchers strongly recommend that medics are inoculated when sown on Mallee soils, even if medic has been grown previously.

More information:

Jake Howie, SARDI,
08 8303 9407,
jake.howie@sa.gov.au;

Ross Ballard, SARDI,
08 8303 9388,
ross.ballard@sa.gov.au

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