Studies conducted through a Grains Research and Development Corporation investment have shown that increasing the rate of inoculant applied to seed improves nodulation where soil conditions at sowing are sub-optimal.
Researchers at the South Australian Research and Development Institute say an increased inoculation rate also provides a practical way of improving nodulation where legumes are being sown for the first time, especially on hostile soils.
‘‘Our results to date indicate that to optimise nodulation when dry sowing, application of rhizobia in high numbers is required,’’ SARDI senior research officer Liz Farquharson said.
‘‘Increasing the rate of inoculant application always improved nodulation.’’
However, Dr Farquharson said some growers had experienced seeder blockages when they have increased the inoculation rate, so she recommended testing a small batch of seed first to avoid such problems.
Dr Farquharson encouraged growers to take particular care if they intend applying rhizobia to seed along with pesticides, especially when sowing into sub-optimal soil conditions.
‘‘Where pesticide application is necessary, granular rhizobial inoculant or a peat slurry in furrow may provide a better option, reducing direct exposure of the rhizobia to the pesticide,’’ she said.
It is hoped a new commercial strain of rhizobia to improve the nodulation of bean and lentil in low pH soils will have a substantial impact in the southern cropping region where pulse production is expanding into higher rainfall areas with characteristically low pH soils.
‘‘We believe that this new strain has potential to improve the production of pulses on around a 100000ha of ground — so it’s quite significant,’’ researcher Ross Ballard said.
If data supports the release of the strain of rhizobia with improved acid tolerance, it is likely to be commercially available in 2021.
Meanwhile, the researchers say that improved rhizobia should be seen as an accompaniment, not a replacement, for liming.
‘‘Liming remains important to prevent further acidification and is critical to the longer term sustainability of the farming system,’’ Mr Ballard said.
‘‘Plant root growth will also likely benefit from the addition of lime and improve overall performance of the pulse crop.’’
Dr Farquharson said research into understanding more about how rhizobia survived and nodulated under a range of stressful conditions was continuing so improved inoculation recommendations could be provided to growers.
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