Pasture legumes support robust rotations
GroundCover™ Issue: 122 | 02 May 2016 | Author: Nicole Baxter
- Summer sowing hard-seeded annual pasture legumes, using seed harvested on-farm, has been a robust method of establishing pastures on Mike O’Hare’s New South Wales property
- Trials show hard-seeded legumes can regenerate vigorously following a cropping phase without the need for resowing
- On-farm monitoring shows annual legumes can support livestock while also offering a means of managing herbicide-tolerant weeds
With subclover failing to persist after drought, one New South Wales grower discusses his use of hard-seeded pasture legumes to reduce the need for resowing after the cropping phase
After successive dry seasons all but wiped out Mike O’Hare’s subterranean clover seedbank on his 2200-hectare southern New South Wales property, the mixed farmer decided to trial hard-seeded pasture legumes as a low-cost way to build a more resilient pasture bank.
Mike, who farms at Beckom, about 110 kilometres north-west of Wagga Wagga, says sowing subclover across 2000ha would have cost $70,000, with the added expense of having to resow new seed every three to five years.
However, by sowing and harvesting hard-seeded pasture legumes comprising a pure stand of Casbah biserrula and a mix of Bartolo bladder clover and Prima gland clover, Mike reduced the cost to $22,500 and, so far, has not had to resow new seed after the cropping phase.
Belinda Hackney, a research agronomist at Charles Sturt University (CSU), says hard-seeded pasture legumes such as biserrula, bladder clover and gland clover can provide a disease break, supply nitrogen to subsequent crops and offer high-quality fodder.
Mike decided to trial hard-seeded pasture legumes in 2009 after meeting Ms Hackney.
The pair established trials on Mike’s farm, where four pasture species – biserrula, bladder clover, gland clover and French serradella – were each sown as individual 8ha blocks.
Mike says 2009 was an ordinary year, well down on rainfall during winter and spring, which stymied the growth of the pastures after they were established in May.
Ms Hackney says although subclover grown in the Riverina region died before seedset in 2009, all the hard-seeded legumes produced seed.
Mike was able to harvest the gland clover, even though the plants were only about 75 to 100 millimetres high, using an open front header. The result was enough seed to sow more than 100ha in 2010.
“Although the pastures were nothing to write home about, the dry season of 2009 showed they were capable of producing a reasonable amount of green feed and seed in a very tough year,” he says.
Ms Hackney says all pasture species regenerated strongly in 2010 on the back of the seedbank established in 2009.
Seed has been harvested in most years since, allowing Mike to sell a portion and use what is left over to sow half his farm to biserrula and the other half to a mix of bladder clover and gland clover.
Mike’s approach is to sow biserrula at 8 kilograms/ha in late February to early March using seed harvested on-farm.
He sends the biserrula seed to be cleaned and scarified to about 50 per cent germination before sowing, while the bladder and gland clover is cleaned but sown unscarified.
The granular inoculant he uses is from the appropriate ALOSCA® group, applied either in summer when the pastures are sown or with the preceding wheat crop. Ms Hackney says the rhizobium survives in the rhizosphere in the absence of the host plant and the biserrula shows excellent nodulation.
The bladder/gland clover mix is established differently. The gland clover seed is summer-sown in February, while the unscarified bladder clover seed is ‘twin sown’ with the wheat crop.
After the wheat is harvested, the pasture is left to grow and set seed in the first year. Sheep are allowed to graze the pasture if the season allows.
Ms Hackney says both sowing strategies enable the pastures to be established concurrently (twin sowing), or at a time when pasture sowing does not compete with winter crop sowing (summer sowing). In both cases, she says, this means the pastures can establish early when temperatures are warmer and produce useable feed earlier in the season.
In the second year, the pasture is left to regenerate before being spray fallowed in spring, before seedset, in preparation for canola and then wheat.
After wheat, the pastures are left to regenerate, which means they only set seed once every four years.
Season 2014 was the first opportunity to measure the regeneration of the hard-seeded pasture legumes following the cropping phase and the impact on subsequent crops.
Mike estimates a 0.5 tonne/ha increase in canola yield following the pasture legumes, compared with his conventional non-legume paddock with only starter fertiliser at sowing. The wheat yield remained the same as on conventional paddocks.
Ms Hackney says the results support earlier research, which showed at least comparable performance of wheat after hard-seeded legumes with no fertiliser addition, compared to non-legume paddocks on which all nitrogen was supplied from inorganic fertilisers.
In terms of regenerating legume productivity, Ms Hackney says the bladder clover and French serradella were similar when measurements were taken in autumn, late winter and spring.
The biserrula pasture had 600 to 1000kg/ha more feed on offer in late autumn compared with the French serradella and bladder clover, respectively. In late winter, the biserrula produced an additional 1000kg/ha of dry matter (DM) compared with the other two species. In spring, the biserrula feed on offer was on average 1600kg/ha more than the other two species.
Ms Hackney says the high feed availability of all species, but particularly the biserrula, in autumn/winter is of substantial value to mixed-farming enterprises and has implications for increased nitrogen fixation for subsequent crops.
At the end of winter 2014, feed on offer in the regenerating biserrula paddock was 4000kg/ha DM, with biserrula contributing more than 90 per cent to total herbage availability.
Mike, Ms Hackney and Dr Jane Quinn (also from CSU) assessed sheep production on the hard-seeded legume pastures under projects supported by Meat & Livestock Australia and Australian Wool Innovation.
In 2014, seasonal conditions deteriorated from late-August onwards. Ewes and lambs were introduced to the pasture on 3 September 2014 and feed availability at that time was 3880kg/ha DM. After measurements ceased when the lambs were weaned, about 1700kg/ha DM remained. Overall, lamb live-weight gains averaged 350 grams per head per day when measured over 56 days during spring 2014.
Ms Hackney says a feature of sowing the biserrula pasture in summer, in particular the variety Casbah, is that it appears to have potential for suppressing early and late-germinating weeds.
She says its lower palatability compared with some other common pasture species means it can also be used as a weed-removal strategy, with sheep eating plants such as annual ryegrass preferentially.
After allowing sheep to graze the biserrula, Mike has noticed fewer annual ryegrass weeds.
Going forward, he hopes to use this as a tactic to help lower the population of herbicide-resistant annual ryegrass plants in paddocks going into crop.
In addition to the weed-control benefits, Mike is hoping that growing a productive stand of biserrula will also decrease the need to add extra nitrogen to his crops.
More information:Mike O’Hare,
0429 782 189,
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