“It’s only really for those with extensive areas of lucerne,” Lincoln University’s Professor Derrick Moot said.
“If you’ve still got plenty of grass to lamb on then stick with rotationally grazing your lucerne from tailing or whenever it hits 15-20cm tall. If you get set stocking wrong you will destroy your lucerne,” he said.
Only where 30% or more of improved grazing area has been turned over to lucerne and quality grass for set stocking is in short supply is when lambing on lucerne should come into the equation.
To avoid opening stands of the legume and letting problem weeds gain a foothold, lambing mobs should be stocked less densely than when rotationally grazing.
“The key is to keep the canopy 15-20cm tall, ie: closed, during that set stock period. You want all the stems productive and keeping weeds out,” Moot said.
Typically that’s achieved with seven to 10 ewes a hectare for about four weeks instead of the normal 12-14/ha for five to seven days when rotationally grazing, he said.
“It’s better to start with too few and to introduce a few more than to put too many on at the start and then have to take some out mid-lambing.”
Another key point is to lamb on only about one-third of the lucerne area so that once the mob has lambed it can be moved into a grazing rotation on the remainder. This is typically at about 12-14 ewes plus lambs a hectare for a week on each block, bringing the lambing blocks back into the rotation after they’ve been spelled for four or five weeks.
An advantage with lambing on a proportion of the lucerne area is it helps avoid the common problem of getting into the grazing rotation too late, Moot said.
“The biggest mistake people make if they don’t lamb on lucerne is they often don’t start on the first paddock until it’s 30-35cm tall and by the time they get to the fifth or sixth paddock it’s 50cm which is too long and too stalky.
“The rotation should start with the first paddock at 15-20cm.”
For lambing on it, if need be, a mob of ewes can be set stocked when the lucerne is still shorter than 15cm but it must be growing well and the stocking rate will need to be reduced a little more than normal, Moot added.
“Whatever height you start at, when you set stock lucerne the canopy should be getting gradually taller, not shorter.
“If it starts getting shorter you’re opening that canopy up and you’re going to have to reduce numbers or move the mob on – as you would when rotationally grazing – pretty soon.”
A strategy that can work well is putting half the late-lambing mob, assuming ewes have been scanned for foetal age, on to lucerne for lambing – effectively a quarter of the flock if there’s a 50-50 split between early and late lambers.
With those ewes milking better and lambs nibbling at the high-quality feed from the outset there’s a good chance they’ll catch up with their counterparts born earlier on grass even if they’re subsequently transferred to lucerne as well, Moot said.
However, he said short-term lamb growth gain shouldn’t be at the expense of lucerne stand longevity, which is why set stocking should be attempted only by those who truly understand the plant’s growth and response to grazing.
There’s no need for a gradual transition of ewes on to lucerne for lambing – they can go straight on to it provided adequate salt and a fibre source, such as hay is offered.
“If they’ve come straight off hard hill country you might need to keep a closer eye on them and put a bit more fibre out or give them access to some grass next door but generally there’s no problem.”
Where lucerne has been contour-sown leaving patches of grass and other vegetation on knobs and hillsides in the same paddock there’s probably no need for the fibre source either, Moot said.
“But you always need to put the salt out there and watch stock when first introduced to any new feed source.”
Ideally, lucerne paddocks used for lambing should be those that were grazed off earliest in autumn and with the best shelter. Post-herbicide retention periods also need to be heeded.
“Lambing on lucerne is something you should have been planning from early last autumn, not something you just decide to do on a whim at the start of set stocking,” Moot said.
“But if you are short of grass and the lucerne’s there then provided you’re careful about it and don’t hammer the stand by putting too many ewes on to it you should get away with it.
“The main thing to remember is that the paddocks that have been set stocked will need an extended period of growing in the autumn to recharge their reserves.”
Gaining momentum
Exactly how many farmers are lambing ewes on lucerne isn’t known, Lincoln’s Derrick Moot said. However, there are people doing it successfully throughout the east coast now and some in central Otago have been doing it for decades without destroying lucerne stands.
A study of those central Otago farms found low stocking rate was a common success factor so that, as Moot puts it, “no plants were ever hammered”.
Work by Lincoln at Ashley Dene Farm has honed these findings, resulting in the guideline to set stock at seven to 10 ewes a hectare at a 15-20cm crop height for a maximum of four weeks. Preliminary results of the Ashley Dene work shows that in two out of five seasons such set stocking on lucerne for lambing increased liveweight produced a hectare compared to those rotationally grazed on lucerne from tailing. Both systems outperformed set stocking on older grass paddocks. There was no significant difference between the lucerne treatments recorded in the other three years – see Graph 1.
Gundy Anderson’s coming up to his fourth spring of lambing ewes on lucerne at Bog Roy in Upper Waitaki.
