FAQ : Lucerne Establishment

What is the time frame between lucerne stands and what is the reason for giving the paddock a break?

There is no set period required between lucerne stands but we usually recommend two years. This allows you to use the nitrogen that may have built up in the soil from nitrogen fixation by the lucerne for a grass or forage break crop. Options include a two year ryegrass or a cereal followed by a brassica that is fed off in early winter to then leave a late winter/early spring fallow. The fallow will store soil moisture before sowing a new lucerne stand in mid spring. But as always it depends.

Reasons for waiting two years before establishing a new lucerne stand in a paddock that was previously in lucerne include:

  • The older the stand the more likely old lucerne roots have built up chemical that inhibits the new stand growing- this is not always the case so you can go straight back into lucerne but there is a risk. How big this risk is and how prevalent in New Zealand with high winter rainfall no-one knows so some people ignore it and go straight back in with no problems. Others swear by two year breaks. This process is documented as about a 50 percent risk of autoalleleopathy (this is a fancy word the chemicals produced by the old lucerne stand building up in the soil and compromising the ability of newly sown lucerne seedlings to establish successfully). Work has been conducted overseas but has not been quantified in New Zealand. This autotoxicity, or if the older plants grab the soil moisture because they have developed their root systems, is also why you can’t really re-drill seed into an existing lucerne stand and expect it to be successful.
  • There is usually a reason a stand has thinned and needs to be re-drilled. Factors include weeds, pest damage, pugging etc. A two year break allows you to recreate a weed free environment and allows you to control browntop, couch/twitch, dandelions, mallow, horehound, thistles and other difficult weeds that can all build up as a stand ages and thins.
  • A two year break allows you to break any insect pest cycle that might also be building up.

Reasons not to wait two years:

  • If you have an establishment failure because of patchy establishment, blocked coulters, insect damage. Under these circumstances you can drill into the stand within the first 18 months to thicken it up. We don’t know how long you can go before the new seedlings will be suppressed by the older plants in the stand.
  • Patches drowned in a one-off ponding event have been successfully re-drilled into an older stand at ‘Bonavaree’. Note: if you have a patch in the paddock that routinely ponds in winter try filling it with a patch of balansa clover in the affected area with a bit of cocksfoot.
  • The old crop was relatively weed free and one year of forage break crops works – and you are prepared to accept the risk of autoalleleopathy.

My four-year old lucerne stand has a poor plant population. What should I do?

A low plant population in a relatively young stand can occur because the plants have self-thinned to a population that the soil can cope with – i.e. on stony soils a sparse population becomes evident quite quickly. If this is paddock is on a deeper soil then the population should still be high unless insects have taken some plants out.

So the first question is why has the population dropped? If it is poor soil then if you chose to overdrill lucerne any new plants will be out competed by those that are already there. If it was an initial poor sowing on a deeper soil then the problem should have been rectified earlier. If you lost plants as the result of water logging at some time through the winter then newly established plants may survive – as long as it was only a one off event.

We haven’t tried redrilling into a four year old stand so we don’t know what will happen. Some plants may survive and yes the older plants may produce a chemical that stops the new ones establishing but to be honest a four year old stand it is a grey area and we don’t know what the outcome would be.

If the lucerne paddock is on a deep soil with a good waterholding capacity some cover needs to be added or you will find weeds invade quickly and you lose the ability to salvage the stand.

An alternative to overdrilling lucerne is to drill in a grass to create a lucerne/grass mix – cocksfoot or ‘Bareno’ brome would be my recommendations. This approach may extend the life of this stand for 3-4 more years and the paddock becomes transition feed for ewes and lambs at lambing before they go onto straight lucerne. I would still treat the mix as a pure lucerne stand for grazing management.

What are our options for renewing flood damaged areas where lucerne died out?

If the area doesn’t flood in most years (i.e. flooding rarely occurs) overdrilling lucerne back into the damaged areas can be successful. This has been achieved in both Marlborough (at Doug Avery’s) and at Ashley Dene in Canterbury. Check out ourblog post to see how it worked.

If the area saturates in most years don’t bother trying to re-establish lucerne – it will drown at the next flooding. Landscape farm the area – choose the most appropriate species/mix to survive the conditions in an average year. In these areas you could try sowing 2 kg/ha of cocksfoot as the companion grass with:

10 kg/ha balansa clover OR

5 kg/ha of a yannicum type sub clover (e.g. ‘Napier’ or ‘Monti’) which tolerate wet soils plus 5 kg/ha of the standard sub clover varieties such as ‘Denmark’ or ‘Woogenellup’.

How important is initial weed control?

A well grown lucerne pasture is too much of an investment if not done properly – the longer it lasts the more cost effective it will be. To maximise investment it is important to get weed control in place before sowing/establishment.

Doug Avery uses two summer fallows to make sure no weeds seed. His lucerne is then direct drilled to stop bringing up new seeds from lower levels. He holds off planting even longer if weeds have not been beaten. Thistles are controlled by grub/spot spray so they don’t invade and reduce stand life. Weeds like horehound should be grubbed and targeted at all times whenever they are on the farm.

Annual weeds which germinate after sowing are usually shaded out by lucerne as the canopy re-establishes after its first grazing. At Lincoln University, we generally incorporate trifluralin prior to sowing lucerne while susceptible germinating weed seedlings absorb the product via the roots. Occasionally, and depending on the weed species that are present, we may apply a post emergent herbicide of imazethapyr (e.g. Spinnaker) and/or 2,4-DB to the seedling lucerne at the recommended growth stage.

In most cases, weeds like fathen disappear after the first year. If weeds are beating the lucerne at establishment you can hard graze the lucerne when it is about 15 cm tall, then leave it to flower before the second graze.

Over time invasion by perennial, taprooted or rhizomatous weeds (yarrow, dandelions, Californian thistles) occur because once a lucerne plant dies, it leaves a gap in the stand where weed seedlings can establish. Their presence should be an indication that the stand is nearing the end of its productive life. These stands can be over-drilled with grass and lambed on before going being targeted for pasture renewal which allows the difficult weeds to be controlled.

What is the latest recommended sowing date for lucerne on an unirrigated, light, stony soil?

It depends… Any time before Christmas is better than after Christmas. The key thing is weed control and hopefully getting some summer rainfall. October would have been better because it gives the seedlings time to establish a bit and develop their root system before being exposed to water stress.

What determines how early I can sow lucerne on the sand country?

Soil temperature- once it is above 8°C and holding you can sow.

On sand country make sure you sow at 15-20 mm – no deeper – and into a firm seedbed that you heavy roll after sowing, preferably with rain due within 48 hours. With sand you may also want to put 20 kg/ha of N as Cropmaster 20 down the spout with sowing because sand has no nutrients and in this situation a little N at establishment may help lucerne get going – this is a unique situation that needs to be treated differently from anything else.

What is the best way to establish lucerne under pivot irrigation?

It depends on the soil type – either way irrigate before sowing to ensure the soil profile is full then drill. Do not irrigate again until the lucerne is all emerged and needs it. For a shallow soil (for example a stony Lismore soil) then don’t let the soil dry out and irrigate as required if the plants start to wilt after they are about 20 cm high.

For lucerne, one irrigation application of 50 mm is preferred over two of 25 mm. If you have a deeper soil then irrigation is probably not necessary at all for an establishing crop. The main thing is not to irrigate too often because the canopy is not fully expanded (i.e. full ground cover) so you will germinate weed seeds. However, keeping the plant actively growing is key – the more it grows the deeper those roots go. And of course let it flower or get to at least 40 cm tall before a first cut or graze. An additional benefit of the less frequent irrigation is that you’ll reduce the humidity in the canopy and this can reduce the development of diseases which can thrive in warm, humid conditions.

Do I irrigate or let lucerne establish without irrigation this season?

There is no need to irrigate initially straight after drilling. You will just germinate a lot of weeds – but once the lucerne canopy has closed an application of water can aid growth and help roots explore the soil. The crop should be irrigated if it starts to get dry – this won’t stop the roots continuing to grow down the soil profile it will actually help them do that. The key thing is to ensure the soil profile had water before sowing. With spring sowing this is not usually a problem.