LUCERNE HAS become the champion of 'the big drought'. See a tinge of green in a paddock anywhere at present and chances are that it's lucerne and that it's still providing feed for stock. It promises to be even more valuable with any summer storms. Past experience says that lucerne will be the first pasture plant to respond and produce more feed. Just how that feed is handled will probably decide the future of the lucerne stand.
But according to Jim Virgona of Charles Sturt University's Fairer Centre, lucerne will be at its most vulnerable after the rain. "Right now the plant is drawing on reserves of carbohydrates and protein it has stored in the crown and tap root. Unless it gets a chance to replenish those reserves after rain, there's a risk of exhausting it and significantly reducing the density of the stand. If you want to keep the stand, give it a rest for a few weeks after substantial rain."
Phillip Eberbach, the director of the Farrer Centre, says that any dryland lucerne stands still producing are probably relatively new stands. "They're drawing on, and producing from, moisture reserves within the top 1.5 metres," he says. Older stands that have mined the moisture down to say 2 metres will have shut down and will be producing little if any leaf.
"Our work at the Centre has shown that lucerne uses deep moisture, say below 2 metres, to survive — not to produce. Old established stands of lucerne will probably have used all of the available moisture down to this depth. But, whether it's a new or old stand of lucerne, provided that the crown has not been damaged by grazing, it will respond quickly to summer rain and growers need to plan on how they'll use that summer feed."
Rotational grazing key to survival
"If you want to save the stand, then don't depart from the principles of rotational grazing," says Dr Virgona, "and allow it to recover before you start grazing. Under ideal conditions this would mean allowing it to flower, but feed will be too valuable to wait that long. I'd suggest a three or four week break after rain to allow the plant to store its reserves."
He added that growers should remain as flexible as possible in their grazing decisions. If the regrowing plants again run out of moisture and become stressed, grazing is one way of reducing the leaf area, reducing moisture loss and making the most of the feed before the leaves dry up and blow away.
Pointing out that there's a natural and continuing decline in the density of a lucerne stand every summer and autumn, Dr Virgona says that future plans for the lucerne paddock will also play a role in the grazing strategy.
"If you have a number of lucerne paddocks and one is slated for a grain crop in 2003 or 2004, you can start the process of removing the lucerne by grazing it first and hard after rain," he says. "If the lucerne stand is required beyond this, then make sure it is well rested after a substantial rainfall event."
Contact: Dr Phil Eberbach (02) 6933 2830