New rhizobium strains better

New rhizobium strains attract immediate demand

Cropping
Growth of field pea where seed was inoculated with different strains of rhizobia. Researchers are now working to determine how new strains might be dry sown.

Growth of field pea where seed was inoculated with different strains of rhizobia. Researchers are now working to determine how new strains might be dry sown.

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Multiple new strains of rhizobium are being evaluated by NSW DPI and the Australian Inoculant Research Group in collaboration with Ag Grow Agronomy and Research and Pulse Ag Consulting.

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RESEARCH teams have identifed two potential acid-tolerant rhizobium strains to help pulse crops fix nitrogen.

Work is currently occurring in the Grains Research and Development Corporation's northern, western and southern regions, with the northern region led by NSW Department of Primary Industries. Current commercial Group E/F inoculant rhizobia strains for field peas, lentils, vetch and faba beans were originally isolated from soils with pH levels greater than 7. When met with soils with pH of less than 5.5, these strains rapidly lose effectiveness.

Recent surveys through central and southern NSW have found more than 60 per cent of cropping soils have pH less than 5.5.

A number of new strains are being evaluated by NSW DPI and the Australian Inoculant Research Group in collaboration with Ag Grow Agronomy and Research and Pulse Ag Consulting.

Ag Grow agronomy and research director Barry Haskins initially trialled some of the strains in 2017.

When the trial results were unveiled at an open day on Ridgetop near Griffith before 150 farmers the question on everybody's lips was: "where can we get some?"

Mr Haskins said the initial trials recorded a 30-per-cent biomass increase in soils of pH 4.8. "Acid soils, heat, dryness and herbicide residues challenge current rhizobia strains, but the new strains appear better adapted," he said. There are now trial sites in Condobolin, Griffith, Wagga Wagga, Tamworth, SA and WA.

DPI project leader Dr Belinda Hackney, said acidity was a 'sleeper' problem, contributing to gradual, but ongoing production drop off.

"We have now evaluated strains identified by Murdoch University and the South Australian Research and Development Institute across soils with a pH of 4.6 to 7.2 and we are seeing consistently higher nodulation with two of the elite strains," Dr Hackney said

There is also work underway to determine the effect of herbicides on the pulse host and rhizobia.

"Herbicides and their residues can reduce the density of root hairs, where rhizobium gains entry to the plant," she said. Mr Haskins said trials had found residues of various commonly-used herbicides resulted in significant damage to pulse crops.

"Growers need to be mindful of herbicides used and how long they may persist in the soil," he said.

The project is now working to determine how effective the new strains are when sown into dry soils.

"Currently, most pulses are inoculated using wet delivery systems like peat or liquid injection. These systems deliver large numbers of rhizobia, but unprotected and in dry soils, they die quickly," said Dr Hackney.

Worldwide search for new rhizobium

SEEKING soils similar to that of Australia's cropping belt has led researchers to countries of a similar latitude in their hunt to find rhizobium suitable for use here.

Areas of Sardinia have sandy, acidic soils on par with much of our cropping country and rain falls predominantly in autumn, winter and spring.

In an attempt to improve the adaptation and performance of pulse crops, strains were isolated from Sardinia where soils had pH calcium chloride of 4.5 - 6 by Dr Ron Yates at Murdoch University. At the same time a team from the South Australian Research and Development Institute led by Ross Ballard was isolating strains from SA.

Strains of acid-tolerant rhizobia identified by Murdoch University and SARDI are now being trialled.

DPI soil researcher Dr Belinda Hackney said acidity had long been a problem for Australian croppers and was a research focus in the late 1990s and early 2000s.

"Great advances were made back then, but the problem never went away," she said.

"But everything old is new again," and now finding ways to improve crop yields in acidic soils commonly found in central and southern NSW was back in the spotlight. Finding acid-tolerant rhizobium strains wasn't the entire solution, she said, lime was still needed.

But she said the price of lime hadn't increased dramatically and commodity prices were strong, meaning modifying pH wasn't the costly exercise it once was.

The Grains Research and Development Corporation is funding the trials.

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