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Hardy legume adds nitrogen in drought

Paul Sinderberry and Sarah Wrigley are replacing subclover and field peas with biserrula to improve the viability of their crop rotation in central New South Wales.
Photo: Nicole Baxter

Paul Sinderberry and Sarah Wrigley are sowing biserrula because the pasture legume persists well and adds nitrogen to soils, especially in dry conditions when pulses struggle and fail to deliver an economic return.

The husband-and-wife team produce grain and cattle across 11,000 hectares north of Condobolin in central New South Wales. The average annual rainfall is 420 millimetres but is highly variable.

Sarah manages the cattle, while Paul oversees 4000ha of wheat, canola and barley on red sandy loam soils.

Paul started searching for alternative legumes because lucerne-clover pastures, grown for five to eight years before cropping, cause bloat in cattle.

In 2016, he heard NSW Department of Primary Industries (DPI) researcher Dr Belinda Hackney speak about biserrula and serradella. Paul talked to her afterwards, asking questions about their potential viability for his farm.

“Belinda suggested we trial arrowleaf clover, bladder clover, gland clover, rose clover, French and yellow serradella and biserrula,” he says.

In May 2017, Paul planted the new pasture species in strips across an 80ha paddock.

Dry conditions persisted from late 2017 to October 2018. One rainfall event was recorded in October.

“The biserrula started growing when nothing else did, enabling cattle to graze the paddock in December,” he says.

Despite the severe drought of 2019, NSW DPI trials at a nearby location showed biserrula provided sufficient nitrogen to support wheat grain yields in 2020 of more than 3.8 tonnes per hectare without the addition of nitrogen.

In 2020, Paul sprayed out his trial and planted oats. He was surprised at how well the biserrula regenerated, unlike the other pasture species.

“In the mixed-farming, marginal-rainfall zone, biserrula can improve the viability of our crop rotation,” he says.

Paul bought 1t of seed and planted it in 2020 as a monoculture. He says biserrula costs no more to sow than field peas, at $50/ha.

“Our 2020-sown paddock is still going gangbusters, and we have harvested it twice for seed using a conventional harvester,” he says. The biserrula is put in windrows with a hay rake before harvesting with a canola pick-up front.

In the past two years, Paul has sown 2430ha of lucerne-biserrula (two kilograms/ha for each species); and 567ha of pure biserrula at 5kg/ha. He aims to run one year of biserrula followed by one year of wheat.

“Biserrula fixes a similar amount of nitrogen as other legumes at 20 to 25kg/t of dry matter,” Dr Hackney says. “However, it emerges earlier and grows for longer than subclover and medic, so more tonnes of herbage are produced, and more nitrogen is fixed per hectare.”

Paul is currently waiting on soil test results, but he is confident the biserrula will have added a bank of nitrogen to the soil because it has been nodulating well.

In future, he will trial summer sowing of biserrula to provide early season feed. Summer sowing eliminates the need to scarify the seed, which is required when sowing in autumn.

He is also building a 12-metre weed wiper to control in-pasture broadleaf weeds.

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