Inoculant Information (1 of 2)

All plants require nitrogen for growth and although this is freely available in the atmosphere it is not in a form that plants can utilise.

Legume plants have the unique ability to fix atmospheric nitrogen by means of bacteria which live in symbiosis on the nodules of their roots.

There are numerous species of these bacteria and each has the ability to nodulate different host plants. These bacteria have been isolated and separate cultures prepared in a peat medium which can be used to distribute the bacteria over the surface of the seed prior to sowing. This distribution over the seed will ensure effective nodulation and thus the process of nitrogen fixation by the host plant.

The beneficial effects of using inoculants can be dramatic

The use of these peat cultures is always advisable when the legume crop or plant is introduced to new land for the first time. In virgin soils the response to inoculant is not spectacular since such soils rarely contain the appropriate Rhizobia. There is evidence that inoculant hastens establishment of the pasture and in most cases more nodules are formed on neutral rather than on acid soils.

In some cases, the soil may already contain adequate numbers of effective bacteria from previous sowings of similar legumes. The conditions may also be adverse for bacteria and the host plant, for example, acid soils, waterlogged conditions, soil too dry or from various deficiencies.

It should therefore be recognised that with so many variables, the use of commercial cultures will help to ensure effective nodulation and that the correct stain of Rhizobium is available in the soil for the host plant. In the early 1930's little more than the maintenance of a small range of mostly imported strains of Rhizobium was attempted. With the advent of the tropical pasture revolution there was a need to accumulate knowledge and to rethink the philosophy and development of the legume-Rhizobium symbosis. Today, there exists very specific strains of bacteria, particularly among the tropical species.

It should be recognised that mixing of inoculated seed with superphosphate for even one hour before sowing will significantly reduce establishment and prolonged contact will completely eliminate the bacteria. Exposure of the inoculated seed to sunlight, high temperatures, dry conditions and many chemicals will also be detrimental to the bacteria and special precautions need to be taken.

Methods of Inoculation

There are many procedures for inoculating seed available and the method chosen depends on a number of factors, such as the expected response to inoculation, the trouble the farmer is prepared to go to, the acidity of the soil and the contact between the seed and the fertiliser etc.

The methods include…

• Slurry Inoculation: Prepare a slurry by mixing the contents of the packet with 1000mls of cool, clean water. Pour this slurry mixture over the correct weight of seed and mix thoroughly making sure that all the seeds are evenly coated.
• Dusting: The peat culture is mixed with the seed and may be carried out in the drill or combine. The seed may be pre-moistened with water.
• Lime pelleting: An adhesive material is used and there are many grades of Methyl Cellulose on the market, some of which are required to be dissolved in boiling water and other in cold water.

Please continue on to Inoculant Application Methods (Inoculant Chart) »