RESEARCH focused on release of rhizobia bacteria strains more acid soil tolerance is a key aspect of better performance of pulse crops like faba beans, lentils and field peas.
Faba beans, lentils, and field peas are being grown into an expanding range of environments, often including soils that can be acidic in either or both the top and sub soil.
Improving the performance of these crops is not only dependent on them having useful acid soil tolerance, a plant breeding aspect, but also having acid soil tolerant rhizobia to coexist with them and better fulfil their role in building soil nitrogen.
Research investigating more acid tolerant rhizobia for these pulse crops is led by Ross Ballard, South Australian Research and Development Institute (SARDI). GRDC part fund the research.
Several experimental rhizobia strains from the South Australian collection in three years of testing on very acid soils are showing improved tolerance and performance.
Healthier active rhizobia nodules in acid soils resulting in greater nitrogen fixation and higher crop yields have been recorded.
A new strain of rhizobia for faba bean and possibly lentil could be commercially available within a few years, subject to further detailed research.
Other research aspects support increasing the rate of rhizobia inoculation (current strains) to improve faba bean nodulation and grain yield in acidic soils.
However, Mr Ballard cautions that growers have reported seeder blockages with increased inoculation rate, so testing a small test batch of seed first to avoid such problems is suggested.
Mr Ballard and colleagues note care is needed where rhizobia are applied with pesticides on seed, especially sowing into acidic soils.
Rhizobia are best applied last and as close as possible to sowing. Where pesticides are necessary, granular rhizobial inoculant may provide a better option.
Mr Ballard stresses, even with good inoculation practice on acid soils, nodulation and soil rhizobial colonisation can be below potential, so the addition of lime is still needed.
Liming to raise pH (Ca) above 5.0 also helps correct deficiencies and toxicities that more broadly limit crop performance.
But improved rhizobia strains will be of enormous benefit even in limed soils, especially where there are acidic sub-surface layers that are difficult to remediate because of slow movement of lime down the profile.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email firstname.lastname@example.org or contact (0428) 752 149.