Not a wonder plant, but an answer for low soil fertility

By Alec Nicol

Listen to Dr John Ayres from NSW Department of Primary Industries Centre for Perennial Grazing Systems at Glen Innes talk about birdsfoot trefoil, and you"ll be convinced he"s working with a wonder plant. When you suggest it sounds better than lucerne he pulls you up:

“No, if soil fertility permits, grow lucerne or white clover, but if it doesn"t, birdsfoot trefoil could be the answer.”

And it could be the answer for as much as 16 million hectares of high rainfall country in eastern Australia.

This acid-soil tolerant, perennial legume has a deep tap root which, if unimpeded, will go down 2.5 metres.

A dense, fibrous root system in the first metre allows it to make effective use of scarce nutrients in poor soils. It is moderately tolerant of water logging, salinity and manganese toxicity; maintains vigorous growth down to pH 4.7 and has the added bonus of being drought tolerant.

It may produce less dry matter than lucerne on better soils but is comparable, if not superior, in feed value. Its stems are less fibrous and it holds its leaves better as it matures in summer, and most importantly it is bloat safe. So, where is it?

The current impetus for developing birdsfoot trefoil for Australian conditions has come through the work of the CRC for Plant Based Management of Dryland Salinity, funded by the GRDC. Improved cultivars of birdsfoot trefoil will provide a new perennial legume for farmers in recharged landscapes where soils are too infertile for white clover or too acidic for lucerne. This will provide a bloat-safe perennial legume that will rehabilitate soil fertility, reduce recharge into groundwater and help overcome dryland salinity.

“The plant didn"t get a proper start in Australia until the 1990s,” Dr Ayres says.

“It has specific rhizobia requirements not naturally present in our soils. Now we have an improved commercial inoculant so that"s one problem overcome, but birdsfoot trefoil is a very particular plant.

“While it is perennial, with individual plants persisting from three to eight years, it requires good seed-set and seedling recruitment to persist, and it needs long daylength for the necessary prolific flowering.”

Birdsfoot trefoil flowers and sets seed in summer and, to perform, needs between 14 and 18 hours of daylength. Sixteen is optimal and for areas with less than 14 hours of daylength, forget it.

Armidale enjoys about 14 hours daylength (on the longest day in December), Canberra about 15 hours, and Tasmania about 15 hours 15 minutes; so Australia is not its natural home. However, there is a lot of genetic variation in birdsfoot trefoil"s daylength requirements and that"s where Dr Ayres has been working.

From half a million plants of Goldie, the only commercially available variety in Australia, he selected 326 that flowered intensively at Inverell in northern NSW.
A second round of selection for seed production made at Glen Innes reduced the number to 28.

A parallel selection strategy with a broad germplasm base brought his total number of elite plants with short daylength requirements and high seeding capability to 46.

Earlier Dr Walter Kelman, from CSIRO Plant Industry in Canberra, had developed a breeding line based on recombination and selection from a strategically selected set of erect and prostrate lines. The result of these programs is three experimental varieties: one prostrate, one semi-prostrate and one semi-erect - now ready for commercialisation.

“Glen Innes is a 14-hour environment, so we"ve pushed the daylength requirements to their limit,” says Dr Ayres. “And the exciting thing is that flowering prolificacy is highly heritable, so for the country south of the Queensland border we"re on the way to removing the second barrier to birdsfoot trefoil production.”

The final barrier to adoption lies with growers. “I often call it "the back paddock plant" - it does well under adverse conditions but isn"t the species you"d choose for a competitive pasture mix in highly fertile soil,” he says. “It has very small seed that germinates readily from the soil surface and it will fail if sown with a highly competitive grass such as perennial ryegrass or under a cover crop. It"s equally pointless to try it with spreading species like kikuyu or other warm climate grasses, but it goes well with clumping grasses such as tall fescue or cocksfoot and we"ve had great success direct drilling it into naturalised grass pastures checked with herbicide.”

The future of birdsfoot trefoil is with the seed industry. Drs Ayres and Kelman have enough seed of their three lines for national field evaluation, and are now looking for a partner to commercialise their experimental varieties for release to industry by 2008.

For more information:
Dr John Ayres, 02 6730 1930, john.ayres@dpi.nsw.gov.au
Dr Brian Dear, 02 6938 1856, brian.dear@agric.nsw.gov.au
Dr Walter Kelman, 02 6246 5083, walter.kelman@csiro.au

The pastures ute guide is available from Ground Cover Direct, 1800 11 00 44, ground-cover-direct@canprint.com.au

GRDC Research code: UWA 397, program 4

Region North