Listen to a podcast of the teleconference:
The lucerne renaissance
Lucerne’s ability to make efficient use of water to grow high quality forage is making it an increasingly popular plant in dryland East Coast farming systems.
The forage has undergone a renaissance in the past decade, as plant scientists such as Professor Derrick Moot have encouraged farmers to graze – rather than cut and carry – their lucerne crops, and have de-bunked many of the management myths about the crop.
Speaking on the teleconference call, Derrick said the main reason for growing lucerne is its deep tap root, which can access soil moisture at a much deeper level than traditional ryegrass roots.
Because it fixes nitrogen (N), lucerne is never N deficient and is able to use every millimetre of water very efficiently. Water use efficiency in plants is dependent on nitrogen availability.
“Pastures that are N deficient do not use water efficiently.”
Heading into spring, Derrick says farmers need to consider what moisture they have available within the soil profile.
This varies between soil types and winter rainfall – so a stony-type soil may be full after relatively low winter rainfall, while heavy Wakanui or Templeton-type soils may only be 30% full.
Derrick says that like any plant, lucerne will struggle to be productive when there is no moisture available and this may be the case for farmers in parts of North Canterbury and Marlborough this spring.
Farmers with soil moisture deficits should just manage the lucerne as they normally would in spring, but cannot expect the same post-grazing recovery as they would get where there is sufficient moisture available.
Because lucerne’s growing points are at the top of the plant, it should be rotationally grazed.
Derrick advises against set-stocking in spring, as stock will remove all the growing points. This will set the lucerne stand back by up to four weeks.
The exception is where farmers have a particularly large area in lucerne, and a small area can be sacrificed for set-stocking ewes at lambing. In these instances, the crop should be very lightly set-stocked over a short period of time.
“It cannot be nailed.”
In a typical rotational grazing situation, stock can be run onto the crop when it is 10–15cm high – ideally at a stocking rate of 14 ewes and lambs/ha – and moved to a new paddock every three to four days.
Derrick says farmers really need at least 20ha of lucerne before they can start a rotation that results in good livestock and forage growth rates – a 5ha paddock is really only a cut-and-carry proposition.
On a five-six paddock rotation, stock will be coming back into the first paddock when the crop is 25–30cm tall, which means it has retained its feed quality.
The flowering myth
Over the past decade, Derrick has debunked the myth that lucerne needs to flower in spring before it can be grazed.
He says lucerne responds to day length – so in spring and early summer, it can get very tall before it flowers and feed quality declines.
“If you wait until 10% of the stand is flowering, then the stem will be lignified.”
In spring, the lucerne plant draws on its root reserves to bring 3T of carbon and N to the surface.
In late summer and autumn, the plant needs to have the opportunity to replenish these root reserves for the following season, so it needs to be spelled for six weeks while it is still actively growing. Often the crop will flower during this time.
Derrick says spelling the paddock any time from mid-January (before it goes dormant in winter) will allow the plant to produce to its potential the following spring.
Weeds and fertility, particularly soil pH, need to be taken into account before establishing a lucerne crop.
Derrick says weeds such as Californian thistle, yarrow and twitch are all particularly problematic in lucerne stands, so ideally a paddock should go through a crop before being sown in lucerne to control weeds and correct the fertility.
Lucerne prefers a pH of 5.8–6.2 as at this level the critical trace elements, molybdenum and boron, are available to the plant.
Phosphorus is particularly important in establishing lucerne as the element is needed by the plant to start both photosynthesis and nitrogen fixation. Olsen. P levels should be in the mid to high teens.
While lucerne needs sulphur, there is typically enough in standard super-phosphate fertilisers to satisfy its requirements.
It typically doesn’t need specific trace elements unless a problem has been identified, but potassium deficiency could be a problem in cut and carry crops.
Derrick says lucerne should always be sown in spring and he recommends carrying out soils tests in the selected paddock during the previous autumn. In areas where soil pH is low and aluminium could be a problem, the soils should be tested to a depth of 50cm–1m to where the tap root will reach.
Once established, Derrick recommends carrying out herbage tests in spring, particularly if trace element deficiencies are of concern.
At Lincoln University, lucerne crops are drilled (either direct-drilled or conventionally drilled, depending on weeds) from the second week of October.
Derrick says once out of the ground, the newly sown crop will often grow to about 15cm and then appear to stop growing.
This, he says, is when the plant is partitioning energy into its root reserves. Once it has done this, the crop will start behaving like a mature lucerne stand.
Weeds are almost inevitable, but Derrick says a light early grazing can help take out weeds in a young stand. Weed control in mature stands can require the use of chemicals off-label. The Lincoln University website contains anecdotal evidence of how farmers have used chemicals in this way.
All stock grazing lucerne will need a salt supplement – no exceptions.
Derricks says lambs should be protected against clostridial diseases before going onto lush lucerne, particularly in spring. A comprehensive pre-lamb vaccination programme should provide adequate cover in early spring, this may need to be followed up with a further vaccination post-weaning.
Red gut is often associated with lucerne and again, this is more common in spring when a lack of fibre in lush crops means the feed passes through the gut too quickly, causing the gut to twist. The addition of good quality (palatable) fibre to the diet can help prevent this. Another strategy is to mow three of four strips in the lucerne stand two to three days before running stock on. The mown, wilted lucerne is high in both fibre and sugar, making it a highly palatable source of fibre.
Poor scanning results in sheep mated on lucerne are the result of oestrogens produced by fungi in the crop. This is a relatively new finding and explains the sporadic nature of this phenomenon, in that it can be a problem in wet, overcast conditions and less of an issue in young lucerne under clear, dry weather. More apparent in young sheep, Derrick recommends removing ewes from high-risk lucerne crops three weeks prior to mating. However, Derrick emphasised the need to balance liveweight advantages from feeding lucerne against any oestrogenic effects of the fungi when feed is in short supply.