FAQ: Lucerne Management – Plant

When can I heavy roll my lucerne without damaging the stand?

Generally late winter (early/mid-August depending on region and winter activity of the cultivar), when stems are short and soft and are ideal for rolling in surface stones. At this stage the stems are usually soft so if they bend they will usually stand back up. If you are unsure, walk across the paddock and see if you are breaking any shoots off. If you leave it too late the stems harden up as they grow and if rolled, they will break off. These shoots die and therefore new stems have to be produced. This delays spring growth.

A second option is to roll immediately after the first spring grazing before the topsoil dries out.

Does frost have the same effect as late grazing on lucerne?

It can but it depends on the timing and the severity of the frost.

As autumn progresses lucerne progressively is able to cope with some light frosting and will keep growing (it adapts to the decreasing temperatures from autumn into winter). However, a hard frost (and we don’t know exactly what level that is) will kill the growing point at the top of the plant. Once this happens the plant cannot keep producing leaves and growing up. This means it will stop gaining height. At the same time the herbage may go black or brown and begin to die. Because the growing point is dead the plant will then start to try and regrow a new set of shoots its base.

If you have had a frost or the herbage starts to look spotted, brown and is dying – quickly graze it all off with a large mob and try to avoid crown damage. This also reduces any population of overwintering aphids and lets the sunlight hit the base of the plant to encourage those new shoots to begin again ready for spring growth.

Once a stand gets to 4-6 years old you can start to see a build-up of dead stems – from grazing and winter die back. Running a set of chain harrows over the stand to knock off some of these old stems can allow new shoots to grow and thicken up the stems.

When can I start grazing my lucerne in spring?

No matter where you are, you can begin spring grazing when your first paddock is 15-20 cm high.

What stocking rate should I use for spring grazing of lucerne?

Stock lucerne at about 12 ewes with twin lambs per hectare. So if you have 20 hectares of lucerne that will be a mob of 240 ewes and twins on the first paddock of 4 hectares. Put them on about two weeks after lambing when lambs are just starting to have a green pick and the lucerne is about 25-20 cm tall. See the Practical Lucerne Management Guide (PDF 576 KB) for details of subsequent stock movements around the paddocks with an aim to be back at the first paddock in around 35 days.

Be prepared to adjust stocking rates throughout spring. Warm wet conditions may allow higher stocking rates or the opportunity to drop a paddock out for hay or silage.

Post weaning, stock at 20-25 lambs per hectare provided spring rainfall has allowed lucerne regrowth. It is more efficient for total liveweight gain to give fewer lambs a total diet of lucerne for 6-8 weeks than many lambs lucerne for 2-4 weeks.

Is it possible to lamb ewes on lucerne or will it damage the stand?

Set stocking is not ideal for lucerne but as long as the stocking rate is low enough that the lucerne is growing ahead of the consumption (getting taller with animals in the paddock), lambing on lucerne for 3-4 weeks in spring may be ok. After this, start moving the mob with lambs at foot on a rotational grazing cycle through the other lucerne paddocks. Return to the set stocked paddock as the last in the sequence, after allowing about 35 days regrowth.

Lambing on a paddock which has been oversown with some grass or on an older runout paddock is recommended (this allows the rumen time to adapt). Most farmers find they can start rotationally grazing the mob when lambs are 10-14 days old because mismothering is rare. Ewes that are accustomed to lucerne tend to walk to the next paddock knowing they will get a decent feed. Any mismothered lambs actually eat high quality feed anyway- compared with grass pastures where the ewes target the clover before the lambs can get to it.

At Ashley Dene, we are currently (2012/13) running an experiment looking at the effects of early spring set stocking, and hope to be able to come up with specific answers and potential management practices for farmers in regard to set stocking during lambing.

How detrimental is it to lamb very low numbers on lucerne/cocksfoot mixes?

Our recent work at Lincoln suggests you could stock at about 8 ewes+lambs/ha for 3-4 weeks (tailing?) and not cause too much damage on a lucerne stand but,
the key factors are:

The lucerne should be growing ahead of the intake so that the lucerne is getting taller while the ewes and lambs are in the paddock (start when lucerne is around 10-15 cm tall)

Spring lucerne growth should see the crop grow taller over the first 2-3 weeks until intake of lamb increases and

Once the feed supply starts to drop below the intake (mean lucerne height starts to decline) increasing stocking rate to eat all of the herbage within 3-5 days and (so in total you have been on the lucerne 3-4 weeks)

Start your usual lucerne rotation of six paddocks

This practice is becoming necessary as people increase the area of lucerne on farm and the lucerne grass mixes are an ideal place to start the rotation

Make sure the paddocks managed this way get extensive flowering in autumn to recover from the spring set stocking and then

Don’t use those full flower stands for mating.

Defining this practice is on-going at Ashley Dene with the aim of further increasing flexibility in lucerne management at this crucial period. We are planning on stocking our set stocked versus rotationally grazed experiment this week with ewes and 2 week old lambs.

Update Summer 2014: Guidelines are now available on our Dryland Pastures Blog.

What is the recommended stocking rate for weaned lambs on lucerne?

The rate for grazing weaned lambs depends on size (and hence feed requirements) in relation to lucerne growth and rainfall which influence feed supply. A good starting rate would be 20-25 weaned lambs per hectare – see our website for details.

Should I leave a 10 cm residual when grazing lucerne or lucerne/cocksfoot mixes?

As always there is no right answer- it depends. If the lucerne is high quality feed eat it. To find out squeeze the lucerne stems when you go into the paddock. If they are soft all the way up (which usually only occurs when the crop is less than 25 cm tall) then the lucerne is all high quality feed. If you can feel the woody base that is tough/hard graze down to that point. The herbage above the break• has an ME of 12 MJ/kg DM and crude protein of at least 24 percent. The lower stem has an ME of 8 and crude protein around 12 percent. (See below on how to do your own ‘break test’).

For lucerne/cocksfoot mixes the cocksfoot is probably as palatable as it will be in spring so it can also be grazed hard. But overriding this is the stock requirements. In spring stock should be the priority so if that means leaving a higher residual to maintain control of the lucerne paddocks three to four ahead then leave a higher residual and clean it up in the next round or later in summer. Alternatively think about dropping out paddock six if it is getting too tall (over 40 cm). This can be conserved.

Some farmers are happy to leave cocksfoot ungrazed but hammer it with ewes post weaning. In this leader/follower system the lambs have the first few days grazing and the ewes follow but in total still only 10 days on at a maximum.

Any residual lucerne left behind may help the next set of shoots grow but it is not imperative to do so in ideal growing conditions in spring. So make your call based on the animals at this time of year – in autumn the answer is plant dependent.

• To conduct a ‘break test’ on lucerne stems:

Cut a stem (take one to five stems of average height for the paddock about to be grazed) and cut them off at the base. Grasp the tip gently and pull it downwards so it bends over to the point at which you cut it. If it doesn’t break it is all soft, young high quality feed. For the taller stems you will find they ‘break’ when bent downwards. This point on the stem is the point where the stem becomes woody/tougher and stem material below this point is of lower quality.

How do I irrigate my lucerne with a pivot?

Rule of thumb: no leaf = no water used…so don’t irrigate or your get weeds.

a) Timing

Essentially irrigation of lucerne is about lots and not very often compared with white clover which is little and often. So if lucerne has been grazed or cut the leaf has been removed and the crop has stopped using water so there is no transpiration. It doesn’t need water immediately after grazing or cutting and irrigation at this time will only germinate weed seedlings and encourage them to grow. Leave irrigation until about 7-14 days after grazing when you can see the new shoots about to spread their canopy. These are then able to use the water and will dry the soil surface out desiccating any new weed seedlings and shading them as well.

b) Amount

The deep taproots of lucerne mean it is best to apply water infrequently in a large amount. i.e. Rather than one pass of 20 mm every week for three weeks – three passes of 20 mm over three days is preferred. This allows the soil water to infiltrate down the profile below the weed root zones. The lucerne will then start using the water closest to the surface again and dry out the profile and out compete weeds.

c) At establishment – seedling crop

Lucerne grows its roots at about 10 mm per day once it has started to grow. Ideally a spring fallow has ensure the soil profile is full of water. Alternatively, ensure field capacity before sowing so the soil isn’t capped once sowing occurs. Then leave the crop to get on with growing. The roots will rapidly explore the soil so that if there is 60 days of growth before the crop needs cutting the roots will be about 60 cm down the profile. In season rainfall can assist the process but frequent irrigation at this time will only lead to weeds. In extreme dry, if the crop looks like it might die, an irrigation may be required before the first cut/graze at bud visible for this seedling crop. Otherwise leave it to grow and then follow the rules above on irrigation once the canopy recovers.

I’m applying for irrigation rights. What pasture will give me the best return for the cost of the irrigation?

There is no right answer to the question of what pasture to grow. Many dryland farmers in the South Island are now working out that the only way they can make money off irrigation is to consider it an investment for their children or grandchildren or to only use it strategically to finish their lambs. Most full conversions go into dairy sooner or later and even they struggle if they have paid too much for the water. Where only limited irrigation is available it is likely to be hugely beneficial to assist finishing your own stock – provided you can manage irrigated pastures with lambs – this has its own challenges compared with a dryland system.

Lucerne is probably the highest yielding pasture under irrigation but how to irrigate changes. The economics of each stock class will vary over time but one option is to continue with a breeding flock and finishing more lambs on lucerne while buying in bulls. This mixed livestock system is being successfully implemented on many dryland properties we are involved with. The advantage is bulls are more gentle on the plant and can be easily sold if things go dry. Most people who have irrigation spread it over a larger area than can be fully irrigated at all times so again the lucerne helps due to its deeper taproot and ability to maintain growth for longer in between irrigation events. It has a longer return rate than pasture because of the depth of root.

In irrigated systems (or those where rain is adequate for growth) the key to yield is actually nitrogen not water. So if you grow grass you will need to apply over 400 kg N/ha to maximise yield.

As a guideline to help:

Lucerne will produce roughly 25 kg of DM per mm of water per hectare that it uses (Note: this is water used by the plant not water applied – the efficiency of this relative to water applied will depend on the irrigation system, drainage etc.). So if you have 1.0 ha and it uses 200 mm of irrigation it will grow an extra 5.0 t DM/ha compared with what you are currently growing. This calculation assumes you have summer dry conditions that restrict pasture growth for at least 6 weeks of the year. Because lucerne is a legume it is seldom nitrogen deficient so it uses that water relatively efficiently. You can expect a similar response from a ryegrass pasture if you irrigate but it will need at least 400 kg N/ha to get that type of response as it can’t fix nitrogen from the atmosphere. In high yielding regions the amount of N required to maximise yield is economically and environmentally prohibitive. We’ve shown both a ryegrass and cocksfoot based pasture at Lincoln under irrigation required 600 to 800 kg N (not urea) per hectare in total. So, in a cut and carry system, to fully utilise your water with pasture you would need to apply over 1 t/ha of urea. Check out the results for cocksfoot (Mills et al. 2006) and ryegrass pastures (Black & Murdoch, 2013) published by the New Zealand Grassland Association.

Our research has shown that grasses can use water as efficiently as lucerne but need a lot more N than is currently applied (or is permitted to be applied) to do that. All irrigated dairy farms in Canterbury are nitrogen deficient – every spring you can see the effects with urine patches prominent in the paddocks. The key factor limiting growth is not the water – it is the nitrogen. So the addition of irrigation water to pasture by itself is actually not helpful. Water added to resident pasture is likely to produce about 8 kg DM/ha/mm used. The grass is usually nitrogen deficient all year. When the canopy of the pasture is closed, N deficient grass and grass pastures non-limited by N deficiency use the water at the same rate. However, the pasture with sufficient N will grow twice as much dry matter as the N deficient grass pasture. So a fully N fertilised grass pasture (which you won’t be allowed) can also give you 25 kg DM/ha/mm of water used.

In Canterbury calculations for water allocation are done on the basis of 20 kg DM/ha/mm of water used. This would be for a well fertilised ryegrass/white clover pasture. But there is little white clover in most Canterbury pastures so many farmers just add urea as it’s easier. The cost of nitrogen is directly related to the cost of natural gas so if natural gas price goes up so does the cost of urea.

In work here at Lincoln we found:
6 t DM/ha per year for dryland cocksfoot – (eight year old ‘Wana’ stand)

10 t DM/ha/yr for the same pasture but fully irrigated (wouldn’t cover the costs of conversion). This increased yield 66% compared to the dryland unfertilised cocksfoot.

15 t DM/ha/yr for the same pasture but fully N fertilised. No irrigation applied and yield was increased 1.5 times more than the dryland pasture and 50% more than by only applying irrigation to an N deficient system (which is why we push legumes including lucerne so hard for dryland farmers).

22 t DM/ha/yr for the same pasture with full water and full nitrogen – cocksfoot grew as much as ryegrass. The yield was more than double that of the pasture getting only irrigation.

Lucerne (either irrigated or dryland) is your best bet to produce DM per mm of water available and the advantage is greatest in the warmest areas.

It’s early December and my lucerne crop is water stressed, wilting and leaves are dying. Should I graze/cut now or leave it until it flowers?

Either graze or cut the lucerne now. If no decent (>50 mm) rainfall is expected in the immediate future the longer you leave it the more leaf will drop off and the lower quality the standing feed will be.

Flowering is not important at this time – it is important to allow flowering at some point in late summer/autumn. After the longest day lucerne perceives the days to be getting shorter, this triggers the plant to start prioritising reserves down to recharge the root reserves it used for growth in spring. This ensures the lucerne is in the best state.

What is the recommended stocking rate for weaned lambs on lucerne in late December?

The stocking rate will ultimately depend on the size of the animals (animal demand) and your lucerne growth and rainfall (feed supply). About 20-25 weaned lambs per hectare available is a starting figure. We recommend that you adjust the mob size as required to complete grazing a paddock in five to seven days (no longer) running a six-paddock rotational grazing system. If your lucerne is getting ahead of you close one of the paddocks for conserved feed (choose a different one every year & remember to replace the nutrients you’ve taken off – check the Fertiliser FAQ Section on requirements).

Does spelling lucerne in early January have the same benefit as spelling in February?

The simple answer is yes. If it is convenient to spell lucerne in January then that is great do so and it will be as useful as later in February in recharging root reserves for early growth next spring – provided the lucerne is actively growing during the period it is spelled.

The more accurate answer as always is it depends. Remember flowering lucerne, or lucerne infested with aphids, can cause problems if used as a flushing feed. Think about the time of spelling in relation to other feed requirements over the next few months. If you can let it flower in January and then use that mature feed for finishing lambs or making hay/silage that is fine.

The aim is that the regrowth of clean stands (aphid and leaf disease free) in autumn should be fresh and able to be used for flushing. If you have no other feed available because things are dry then think about how you can present ewes with quality feed at flushing – lucerne regrowth about four weeks old would be ideal.

Why are there dark green patches in my lucerne paddock?

In newly established lucerne: New lucerne stands tend to rely on soil nitrogen reserves rather than “paying” rhizobia to fix atmospheric nitrogen into a plant usable for them. This is because the plant has to supply carbohydrate to the rhizobia bacteria whereas the uptake of soil nitrogen, when available, doesn’t cost as much in energy terms. Once the soil nitrogen is depleted – or when the supply is insufficient to meet the plant demand during active growth then it will start paying the rhizobia.

In an established, but water stressed, lucerne stand the green patches are most likely to be urine patches. Established stands have usually depleted the freely available soil nitrogen and are relying on the rhizobia bacteria to supply their nitrogen requirements. As the soil dries the plant grows less and therefore the need for nitrogen from the rhizobia decreases (basically there’s no point in paying for something the plant doesn’t need). However, if the plant is able to respond, the urine patches from grazing animals increase the soil moisture and freely available nitrogen in the urine patch. The plant can use this moisture and nitrogen for growth while the surrounding areas are still water stressed. Also because there is nitrogen in the urine the moisture available for growth in that patch will produce more dry matter for the water used than the surrounding areas (because nitrogen deficient crops/pastures don’t use water as efficiently as crops with sufficient nitrogen for growth).

Why have the roots of my lucerne plants reached a certain depth and then turned horizontal?

This suggests localized aluminium toxicity – the horizontal roots are a classic example of aluminium in a sub soil (see photo below). This is one reason we advocate soil testing to 15 cm and then again from 15 to 50 cm if possible. This will allow the subsoil concentration of aluminium to be determined. Values above 3 mg/kg soil are considered harmful to lucerne and cause the horizontal root growth. If during the dig you find you have several lucerne roots gong straight down this suggests the aluminium is quite localized in patches in the soil. This is a major problem in some areas of the high country and Central Otago.

Effect of aluminium toxicity – lucerne roots growing horizontally at Lees Valley, Canterbury (17/1/2008).

An application of lime before ploughing will allow soil a change in soil pH down to ploughing depth. This will ensure the aluminum becomes plant unavailable. However, the progress of the effects of lime down the soil profile is extremely slow. It can takes several years to move 5 cm. Shallow lucerne roots are less of an issue in a high rainfall environment where frequent rewetting occurs- here weeds are more likely to be a problem. In drier environments the horizontal roots prevent the lucerne accessing soil water at depth and limit the potential production from the system. Lucerne roots are more susceptible to aluminum than most other legumes.

When is the best time to overdrill annual ryegrass into my runout lucerne to extend stand life and what herbicides are required for weed control?

The decision to extend stand life of a runout pasture depends on the weeds which are present. If the stand is running out then using a short term ryegrass is a stop gap- sow as the season allows in autumn after a hard graze of the lucerne. The annual ryegrass will overtop most weeds and outcompete any establishing winter annuals like barley grass, Poa annua and chickweed (Stellaria media) so they shouldn’t need chemical control.

Then the issue is timing of stand renewal – if you are going to plough next spring again why worry about the weeds? Deal with them in the intervening crop phase. This is assuming the weeds are not horehound –which must be dealt with on a continuing basis (see FAQ on horehound control in the Weeds & Herbicides section).