Australian Mungbean Association
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Inoculating mungbeans is worth your while
Inoculating mungbean seed with rhizobia is the only way to enable mungbean plants to 'fix' their own nitrogen from the atmosphere.
13 November, 2018
by Kerry McKenzie, PulseAg Consulting
It is widely known that as a pulse crop, mungbeans have the ability to fix their own nitrogen when the correct rhizobia bacteria are supplied. It is also well known that mungbeans don’t fix very much nitrogen, however there are ways to ensure this is maximised.
To grow a 1 t/ha mungbean crop requires approximately 70 kg/ha of nitrogen, if there are no other limiting nutrients. This nitrogen can be supplied to the growing plant from soil reserves, applied fertiliser or nitrogen fixed from the atmosphere.
While most people don’t like the job of inoculating mungbeans at sowing time, getting it right can provide the nitrogen that the crop requires and ensure maximum yields.
The correct rhizobia strain (Group I) can be found in two formulations – the well-known peat based inoculant and as a freeze dried formulation. Both of these product can be applied as a slurry to the seed or water injected during the seeding process. Both work well so the choice is down to what suits your situation best.
The inoculation process starts from the time you pick up the inoculant from your preferred supplier. Keep the inoculant cool and out of direct sunlight, refrigeration is even better but do not freeze the inoculant. Clean all containers, tanks and lines used for mixing and delivery of inoculant. Contaminants such as zinc and other heavy metals will kill rhizobia bacteria very quickly. Always use potable water when mixing with inoculant. The water should be ‘soft’ and as close to a neutral pH as possible.
Keep seed that has been treated with the inoculum slurry as cool as possible to ensure maximum rhizobia survival, and plant into moist soil. While the manufacturers’ state that peat inoculum can be on seed for up to 24 hours and freeze dried product 6 hours, I suggest that growers should only treat the quantity of seed that can be planted in a 6–8 hour period, and that treated seed needs to be kept in the shade in the paddock. High ambient temperatures at planting time reduces the length of time that rhizobia can be expected to survive prior to planting.
For those using water injection to deliver inoculant, use application rates of at least 50 L water per ha, and preferably 100 L/ha. The stream of water needs to applied with or below the seed. If the soil trench fills with soil before the inoculant comes in contact with the seed, no nodules will be formed.
There are many more aspects to maximising the nitrogen fixation process and further information is available on the AMA website, however it all starts with getting the basics right at the beginning, as there is no coming back from poor inoculation at sowing. If no nodules form there is no ‘free’ nitrogen available to grow your bumper mungbean crop.
I am often asked whether it is worthwhile inoculating mungbeans and my response is always that inoculating is relatively cheap insurance to ensure you give mungbeans the best possible chance of meeting their yield potential.
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