Friday, March 29, 2024

Lucerne smokes grass

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This year’s extremely dry conditions across much of New Zealand reinforced the value of forage systems that perform in dry environments. Sandra Taylor checks out the winners and losers. A comparison of different forages and forage mixes over nine years showed lucerne to be the outstanding performer. Dryland grazing trials on Lincoln University’s Ashley Dene farm compared the forages as part ofthe Pastoral 21 programme led by Professor Derrick Moot. Lucerne outyielded ryegrass in eight of the nine years. Annual drymatter (DM) production across the trial plots ranged from 5.7 tonnes to 18.5t DM/ha, highlighting the huge variability in productive potential among different pasture species. Moot said ryegrass and clover pastures died-out at a rate of 10% a year from the time they were sown, with weeds encroaching on lost pasture.
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“It was a great of example of how ryegrass and clover pastures don’t perform in a dryland environment.”

Cocksfoot proved to be the most persistent dryland species and a mix of cocksfoot and subterranean (sub) clover only lost 3% of the sward every year.

This meant at the end of nine years the trial plots still contained 60% of the original cocksfoot and sub clover pastures.

The pure stands of lucerne remained 90% pure after nine years, assisted by a winter weed control programme. The trials highlighted the importance of getting nitrogen in the forage system to drive water-use efficiency.

In the cocksfoot and sub clover plots, the nitrogen from the clover drove cocksfoot production and made the plant more water-efficient and palatable to stock in summer and autumn.

Moot pointed out that being winter active, sub clover worked best with cocksfoot – white clover becomes active too late in spring to benefit cocksfoot production.

“Nitrogen is the biggest inhibitor to pasture production in this country,” Moot said.

He stressed the importance of using all available moisture in dryland farming systems.

“Nitrogen is our friend but we tend to be scared of using it. It is important to remember that nitrogen will increase water-use efficiency.”

Legumes are the cheapest and most effective way to get nitrogen into a pastoral system. Every one tonne of legume grown will fix 30kg of nitrogen out of the atmosphere.

Pastoral 21 is jointly funded by Beef + Lamb NZ, the Ministry of Business, Innovation and Employment, DairyNZ and Fonterra.

Grazing management

The resurgence in the popularity of lucerne was indicative of its value as a forage. Being a legume, it fixes nitrogen and produces a flush of growth in spring – exactly when high-quality feed is needed for lactation and lamb growth.

While it grows well in spring, lucerne must be spelled for a period in autumn to allow the plant to build root reserves. 

In response to farmers’ demand for greater flexibility of lucerne management in spring, Lincoln has been running grazing trials looking at how lucerne can be used for ewes at lambing.

Moot said lucerne can be set-stocked for lambing providing the stand is a minimum of 10cm, stocked lightly and not overgrazed.

Last year, trial work included set stocking lucerne stands for 14-16 weeks. The result was a huge weed burden in these stands. However, he said they expected this to happen having pushed the envelope in terms of management.

Six years of trial work showed that, overall, there was little difference in livestock performance in terms of total pre-weaning liveweight production between the set-stocking and rotation grazing regimes.

Moot stressed that set-stocking on a lucerne stand was not the same as setstocking on grass-based pasture because the stocking rate needed to be much lower on lucerne and the herbage kept at a minimum height of 10cm.

He recommended set-stocking lucerne at no more than seven twin-bearing ewes a hectare. This ensured that feed continued to grow under the animals and kept the canopy intact.

“If you open the canopy up you are destroying your stand.”

Lucerne rhizobia are particularly hardy and can tolerate several months of moisture restriction. Moot recommended peat inoculant to help generate good yielding crops.

Once the crop has germinated, it needs to flower. When it has reached a height of 15cm it will typically stop growing for a period because the plant was putting energy into developing roots. It might take two seasons for lucerne to fully establish its root system, but this was critical to the success of the crop.

At 15cm the stand can be grazed, but it must then be allowed to recover until it flowers. The weed fathen can encroach on new lucerne stands, but Moot said it will only be in the crop for the first spring – the lucerne will beat it.

Patchy or washed-out areas can be redrilled within the first 12 months. Ashley Dene uses a sowing rate of7kg/ha which is 3-5kg/ha less than is typically recommended by seed companies.

He said this was possible because they ensure they have a well-prepared seedbed. Once established, sulphur deficiency can be a problem on very light soils. Unless the crop is being cut and carried,

Moot doesn’t recommend potassium dressings since this nutrient is returned to the soil through urine. Herbage tests were the best way to determine nutrient deficiencies in lucerne.

Supplementation

A pilot study showed there was little advantage in providing a barley supplement to sheep on lucerne.

The theory was that barley provides extra energy to process the nitrogen in lucerne and increase liveweight production.

Pure swards of lucerne were split in half and grazed by a mob of ewes and lambs. One half of the mob were given access to grain through an Advantage feeder.

Lamb liveweight production was unaffected by the grain, but the ewes given the grain did gain an average of 1.1kg/head up until weaning. In contrast the ewes without the grain lost 1.2kg liveweight.

The net effect was that the grain-fed ewes were 10% heavier than the nongrain mob at weaning. Because drymatter yields were the same in both paddocks, the grain was the most likely cause of this weight gain.

A cost-benefit analysis was needed to determine whether the cost of barley supplementation was justifiable to maintain ewe body condition.

This year the ewes will be shut-off from using the grain feeder once the lambs have learnt how to use it. This will indicate whether grain supplementation was a useful tool in driving pre-weaning growth rates.

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