Freeze dried soluble legume inoculant
Inoculants containing freeze-dried rhizobia are available as soluble powders in 30g glass vials. They become active when the powder is reconstituted with liquid. The product also comes with a pack of protecting agent, which assists rhizobial survival during planting. A vial will treat between 25-200kg of pasture seed depending on the species.
These products allow for spray application, as their formulation is a suspension, and can be directly injected into the seeding furrow or the seed can be coated immediately prior to planting (without adding lime).
Treated seeds need to be drilled into moist soil within five hours of application. Avoid contact with pesticides and fungicides. These products have a shelf life of up to three years when stored at between 4°C and 10°C and not opened.
How to apply freeze dried inoculant
Remove cap and rubber bung from the glass vial, add water, replace bung and shake to dissolve the powder until all the powder is dissolved. For liquid injection add the vial of inoculant solution to 2L of cool water containing protecting agent.
Add this solution to the spray tank and deliver between 50-200L of clean water per hectare into the furrow during pasture sowing. To coat seed add dissolved solution from the vial into 2.5L of water (containing protecting agent) until evenly coated. Allow to dry before seeding.
Granular inoculants
Granular inoculants are stand-alone products that can simplify the delivery of rhizobia to the seed. The technology is an alternative to the labour intensive slurry mix-lime process and can provide greater flexibility in sowing operations (such as sowing ahead of rain). Note that dry sowing can increase the risk of establishment failure from false breaks of season.
The physical separation of the rhizobia from the seed also allows insecticides and fungicides to be applied to the seed, which would otherwise be damaging for the rhizobia. Granules are manufactured from either peat or clay and must be drilled with the seed to ensure rhizobia are placed in close proximity to the seed (Figure 2).
The Group types for each pasture species are the same as for peat-slurry inoculants (AM, AL, B, C, S - see Table 1). When sowing mixtures of legumes, the full rate of granular inoculant for each Group should be used. Avoid contact with free water when sowing seed with granules.
Clay-based granules
Clay-based granules are normally applied at 8-10kg/ha when sowing on 18cm row spacings. The granules should preferably be mixed with the seed at sowing, or distributed through a third box and drilled with the seed.
Excessive auguring should be avoided to minimise dust. They are particularly effective in coarse textured soils and higher rates are recommended for fine textured soils. Clay-based granules are air dried and can be stored for over six months without refrigeration. Store granules in a dry, cool area away from direct sunlight.
Peat-based granules
Peat-based granules are normally applied at 6kg/ha when sowing on 18cm row spacings. These granules must be stored in the same manner as peat cultures (with refrigeration), and sown with seed into moist soil. Do not mix granules with fertiliser.
Pre-coated seed technology
Some seed companies sell pasture seeds that contain rhizobia as part of a complex seed pellet, which may also include insecticides, fungicides and micro-fertilisers. The main use of pre-inoculated seed is for lucerne and annual medics, because the rhizobia for these species survive well in this form. If purchasing pre-coated seed for clovers, serradella and biserrula, ensure the seed has been freshly coated, as rhizobia for these species will die to low levels after three weeks.
Inoculant quality control
Purchase inoculants that have been passed through an independent control system for a guarantee of quality. The Australian Inoculants Research Group, formerly known as the Australian Legume Inoculant Research Unit, conducts independent testing of inoculant quality and certifies acceptable products with a registered trademark.
Interaction between nodulation and nitrogen fertiliser
Nodulation and nitrogen fixation can be reduced if high rates of fertiliser nitrogen are applied with the seed or there are high soil nitrate levels. Added starter nitrogen should not exceed 10kg N/ha for new legume sowings.
Please consult product guides for specific technical information and instructions for use.
Acknowledgements
Information provided here has been produced from research partly funded by the Grains Research and Development Corporation through the National Rhizobium Program to support inoculation technologies.