Rhizobia make friendly fertiliser
From the December 2008 edition of Agriculture Today.
Biological nitrogen fixation where rhizobia in legume root nodules convert atmospheric nitrogen into ammonia for plant growth is one of the great success stories of applied soil biology.
"In an era of rising costs, the role of rhizobia to manufacture environmentally friendly nitrogenous fertiliser is more important than ever," NSW Department of Primary Industries researcher, Greg Gemell, said.
According to Dr Gemell, based at Gosford Horticultural Institute, the replacement of N fertiliser with biologically-fixed nitrogen was estimated to save Australian agriculture approximately $3 billion per year.
Legumes provided an economically and environmentally sustainable source of N and usually soil N increases where they were grown.
Biological nitrogen fixation is optimised when the correct rhizobia were applied to seed or in furrow at sowing (inoculation).
As the legume grew, root nodules formed and the rhizobia within the nodules converted atmospheric nitrogen to ammonia necessary for plant growth.
In pastures, subterranean clover for example could fix 25 to 100 kilograms of nitrogen per hectare per year and lucerne more than 100 kg N/ha/yr.
In grains, yields could increase 50 to 150 per cent (between 0.7 and 2.0 tonnes of grain/ha) when farmers used high quality legume inoculants in N-deficient soils that contained few or no rhizobia.
Inoculants come in various forms; peat-based, granules, freeze-dried and liquid.
For more than 50 years, the Australian Legume Inoculants Research Unit and its predecessors located at Gosford, have controlled and maintained the quality of legume inoculants.
Today, farmers can buy legume inoculants that contain highly effective nitrogen-fixing rhizobia.
These rhizobia are carefully selected after many years of assessment through ongoing research and development programs.
Each year, the research unit supplies more than 35 quality tested rhizobial strains covering 90 legume species to inoculant manufacturers.
These are used for production of commercial inoculants.
Manufacturers are committed to producing quality legume inoculants and frequently submit samples from some, but not all batches of inoculants, to the Gosford research unit for quality assessment against set standards.
The standards assure that the legume inoculant contains the recommended rhizobial strain for optimal nitrogen fixation by the legume, the correct number of rhizobia needed for prompt and adequate nodulation, and no contaminating micro-organisms greater than the acceptable level.
"The consequences of using low quality inoculants are dire," Dr Gemell said.
"The use of the DPI quality assessed and approved inoculants is strongly recommended."
The financial loss due to nodulation failure of legumes because of poor inoculant quality could exceed tens of thousands of dollars.
To verify whether an inoculant is part of a batch that has been assessed by DPI, look for the following statement: "It is guaranteed that a sample from the batch of cultures of which this culture is part has been tested and approved by the Australian Legume Inoculants Research Unit".
The research unit’s laboratory is a NCSI QMS ISO9001:2000 Certified Laboratory
Contact Elizabeth Hartley or Greg Gemell, (02) 4348 1948, or David Herridge, (02) 6763 1143.
