Italian connection gives local peas a fighting chance

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Field-pea-nodulating bacteria strains from Italy and Australia are being used to develop inoculants to maximise nitrogen fixation in acidic soil

Photo of field peas

Established cross-row experiment of Kaspa field peas at Colin and Anna Butcher's farm in Brookton, WA, in August 2014.

The commercial field pea bacterial inoculant strain SU303 is being performance-tested in a bid to overcome challenging soils in Western Australia.

A project led by the Department of Agriculture and Food, WA (DAFWA), as part of the GRDC-funded National Fixation Program (NFP), brings together researchers throughout Australia who are working to maximise nitrogen (N) fixation in grain legumes.

It builds on trials in WA that revealed N fixation is being compromised by acidic soils. Consequently, researchers are seeking a new acid-tolerant field pea rhizobial strain.

The goal is to develop an inoculant that can optimise N fixation in acidic soils to ensure growth and survival of the legume host and its associated root-nodule bacteria.

Developing commercial inoculant strains is no easy task. Many strains have to be screened to assess their ability to maintain high N fixation over a broad range of field pea cultivars and to adapt to the host legumes’ soil conditions.

In this project researchers identified a limited number of rhizobial strains in the national genebank at the Centre for Rhizobium Studies (CRS) at Murdoch University.

The answer to this was to collect field pea rhizobial strains from nodules of field pea plants growing in acidic soils elsewhere in Australia and the Mediterranean basin. The low-pH soils of Sardinia, Sicily and Reggio Calabria (in southern Italy) delivered 85 new strains, while another 25 naturalised strains were collected from Australian soils. These strains were then isolated and tested for N fixation effectiveness in the CRS glasshouse.

Of these, 22 strains with the highest N-fixing capabilities were analysed for survival and persistence in acidic soils during a two-year on-farm trial at Brookton, WA, in 2014–15.

At least 10 of the new field-pea modulating strains produced equal or offer more fixed N than the current commercial strain.

The trial uses a ‘cross-row’ technique to monitor how the 22 strains perform in pH 4.5 soils by comparing their N fixation with the commercial inoculant SU303.

The cross-row technique is a method of selecting the best strain of rhizobia in target soils (in this case low-pH, sandy, infertile soils) to achieve maximum production through optimised N fixation (not only in the growing year but also high N residues for subsequent non-legume crops).

Strains that survive the soil conditions into the second season are expected to have the traits required for rapid colonisation of the field pea rhizosphere when inoculated onto field peas, or delivered as granules.

It is early days, but researchers already know that at least 10 of the new field-pea-nodulating strains produced equal or more fixed N than the current commercial strain. This is encouraging as SU303 is thought to be a very efficient strain for N fixation.

The next step is to measure persistence and colonisation characteristics of each strain during the 2015 growing season. The two best-performing strains will be further tested against the commercial strain at different national field sites in 2016–17. The commercial development of a new field pea acid-tolerant strain will depend on these results.

If this project does support the development and delivery of a new high-quality field pea inoculant for efficient N fixation in low-pH soils, it will be another tool for ‘free N farming’ to support reduced N fertiliser use.

More information:

Dr Ron Yates, DAFWA and CRS, Murdoch University,

ronald.yates@agric.wa.gov.au

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GRDC Project Code DAW00221

Region Overseas, West