Use approved legume inoculants and rest easy

Legumes may not grow without inoculation. The yellow lines show very small, uninoculated clover plants. The lush green clover on the right was inoculated.

While Australian farmers arguably have the best legume/pulse inoculants in the world, few know how this major benefit was derived. Most farmers would probably ask "AIRC-who?" if you asked them about the Australian Inoculants Research and Control Service (AIRCS).

In fact, this NSW Agriculture unit, based at the Gosford Horticulture Research Station, has overseen the quality of legume inoculants used in this country for almost 30 years.

Because of this, inoculation of legumes is now a well accepted practice in Australian agriculture, and has underpinned the establishment of millions of hectares of pastures as well as the development of successful pulse cropping industries.

Pulse legume crops alone fix around $150 million worth of nitrogen each year in Australian cropping regions. The pasture species fix many times this amount, in the range $0.5-1.0 billion.

What are legume inoculants?

Inoculants are packets of finely ground peat containing millions of microscopic bacteria, called rhizobia. The inoculant packets contain a single strain of a highly effective rhizobia for a specific host legume or group of legumes.

The Australian inoculant manufacturers produce about 40 different types of inoculant, covering 90 species of legume. Each different type is clearly labelled for the legume species that it covers.

When used as directed on the packet, inoculants promote the formation of nodules on the roots of the inoculated legume. These nodules are like little fertiliser factories, converting atmospheric N into plant N. This nitrogen (N2) fixation process supplies our legumes and the soil in which they grow with free N.

Why are Australian inoculants so good?

There are two good reasons why we produce the best inoculants in the world. Firstly, the state departments of agriculture, CSIRO and the universities maintain a longstanding commitment to rhizobia and inoculants R&D. A large part of the research aims to select new, highly efficient strains of rhizobia for all of the legumes/pulses grown in Australia and to continually improve the processes involved in manufacturing the familiar peat-based inoculants.

Secondly, we have AIRCS which, as well as its role in quality control, effectively links the Australian R&D program on rhizobia and legumes to the commercial manufacture of legume inoculants. This means that AIRCS-approved inoculants have not only benefited from the independent quality control but also contain the latest research findings and innovations.

Benefits of inoculation

Inoculating legumes is cheap, costing less than $4/ha, yet can result in an extra $200-300 worth of N in the crop or pasture. With the example of soybean on the Liverpool Plains, NSW (see table), inoculation increased nodulation from almost zero to 100 per cent. Grain yields were increased by about 1.5 t/ha, worth $600/ha, dwarfing the $4/ha cost of inoculation.

The bottom line — use only AIRCS-approved inoculants and avoid nodulation failure in the paddock.

The cost of legume nodulation failure is substantial. What if the market was suddenly flooded with lowquality inoculants either produced locally or imported from overseas? The simple answer is that such a development would put at risk the production of grains such as lupin, chickpea and faba bean, and livestock, and would cost the individual farmer or producer money.

The cost of a nodulation failure of the 100 hectares of the Liverpool Plains soybean in our example would be $60,000. Clearly, farmers should continue to use highquality, AIRCS-approved legume inoculants for the best yield outcomes.

Inoculation methodNodule massPlants nodulatedGrain yield
(mg/plant)(%)(t/ha)
Seed - gum sticker1241003-4
Spray - in seed rows76993-5
Not inoculated0.342.0

*Dr David Herridge is Principal Research Scientist at the Australian Inoculants Research and Control Service.