As we said in the last Gold Nugget if you want legumes to produce their own nitrogen, you need to have the correct species of rhizobium in your soil.
There is considerable diversity in the species of rhizobium used by Australian acacias and native peas, which reflect the vastly different ecosystems in which they grow – wet forest, salt affected soils, arid soils, alkaline soils, acidic soils. Some use the same rhizobium as cow peas, beans and lablab, so if you are wanting to try those, take some soil from under a wattle tree growing in moist soil of moderate acidity and either soak the seed in a muddy solution of it, or spread it around the germinating crop. The rhizobium for peas, vetch, broad beans and lentils is likely to be already present in an established garden soil. Once a rhizobium species has been introduced into a soil it usually stays there even if there are long periods without a host plant. Greatest benefits to inoculation occur for crops not previously grown in that soil, or where conditions have not allowed the rhizobium to flourish.
It is uncertain if honey locust and carob have a rhizobium association. There are no root nodules formed, but some researchers are of the opinion that with these plants the rhizobia work via a different mechanism. There are a few non-native acacias which are also not nitrogen fixing.
Inoculants are available in different formulations: peat, freeze-dried and granular. There is also a liquid formulation for soybeans. The inoculants must be stored and applied according to specific directions which will come with the product. Formulations must not be frozen; some can be kept at 4 degrees, others in a cool dark place away from sunlight. When mixing, the container and the water must both be free of pesticide and fertiliser residues, the water of drinking quality. Stir in the open to evaporate chlorine. Granules are placed directly in the planting furrow, while the other formulations can either be applied to the seed before planting, or placed in the furrow. Once mixed with the seed the product has to be used the same day and the seed sown in moist soil. Check the expiry date on the packet. The packet should be marked with the logo of the Australian Inoculants Research Group, which ensures quality control.
The Rhizobiaceae family consists of at least six genii of nitrogen fixing bacteria:
Rhizobium; Bradyrhizobium; Sinorhizobium; Mesorhizobium; Azorhizobium; Allorhizobium
Within each genus there can be several species, and within each species several strains. Some other bacteria genii from different families also fix nitrogen through nodules, including Burkholderia and Methylobacterium.
For further reading: Inoculating Legumes: A Practical Guide, http://pir.sa.gov.au/search?query=inoculants+for+legumes).
Ref: Seedbed The Newsletter Of The Organic Agriculture Association Inc. Winter 2016 Alan Broughton