Legume inoculant buying guide

Choose the Right Legume Inoculant

Legume inoculants contain beneficial rhizobia bacteria selected to work with particular groups of legumes. When the correct strain successfully colonises developing roots, it can form nodules that allow the plant to fix atmospheric nitrogen.

Seedmart supplies legume inoculants for green manure crops, cover crops, pasture legumes and other agricultural plantings throughout Australia. Our range includes inoculants for lupins and serradella, peas and vetches, faba beans, lucerne and medics, tropical legumes, pigeon pea and lablab.

The most important step is choosing the inoculant group that matches the legume being planted. Rhizobia are host-specific, so one inoculant should not be assumed to work across all legumes.

Why Inoculate Legume Seed?

Support Nitrogen Fixation

Compatible rhizobia can form root nodules that convert atmospheric nitrogen into forms the legume can use.

Encourage Nodulation

Applying the correct inoculant helps introduce suitable rhizobia where effective populations may be absent or inadequate.

Support Plant Growth

Well-nodulated legumes are better able to meet their nitrogen requirements under suitable growing conditions.

Improve Rotations

Legumes are commonly used in green manure, cover crop and pasture rotations to introduce biological nitrogen into farming systems.

Useful for New Plantings

Inoculation is particularly useful where the compatible legume has not been grown recently or suitable rhizobia may not already be present.

Treat Small or Bulk Seed Lots

Different inoculant pack sizes allow treatment of smaller garden quantities through to larger agricultural seed lots.

Which Legume Inoculant Do I Need?

Legume inoculants are divided into groups because different crops require different rhizobia strains. Always select the inoculant according to the crop being planted rather than choosing by price or pack size.

Legume or Crop Group Recommended Inoculant Typical Crops
Lupins and serradella Group G Narrow leaf lupin, albus lupin, yellow serradella, slender serradella, pink serradella and related species.
Peas, vetches and lentils Group E Field pea, common vetch, bitter vetch, purple vetch, woolly pod vetch and lentil.
Faba and broad beans Group F Faba bean, tick bean, broad bean and related Vicia species.
Lucerne and medics Group AL Lucerne, alfalfa, strand medic, disc medic and related medic species.
Tropical pasture legumes Group M Siratro, butterfly pea, puero, tropical kudzu, velvet bean, phasey bean, calopo and glycine.
Pigeon pea and lablab Group J Pigeon pea, dolichos lablab, hyacinth bean, perennial horse gram and related species.

Match the inoculant to the legume. Rhizobia are not universally interchangeable. Using the wrong inoculant group may result in poor or ineffective nodulation even if the seed germinates normally.

How Legume Inoculants Work

Step 1

Rhizobia Reach the Root

Compatible bacteria applied to the seed survive long enough to contact emerging roots after germination.

Step 2

Nodules Develop

The bacteria establish a symbiotic relationship with the host legume and form specialised nodules on the roots.

Step 3

Nitrogen Is Fixed

Within active nodules, atmospheric nitrogen is converted into compounds the plant can use for growth.

Step 4

The Legume Supplies Energy

The plant supplies carbohydrates produced by photosynthesis to support the rhizobia living within its nodules.

Result

Biological Nitrogen

Effective nodulation helps the legume meet more of its own nitrogen requirement rather than relying entirely on soil nitrogen.

Rotation

Benefits Future Crops

When legume residues are returned to the soil, some of the nitrogen contained in the plant material can become available to following crops as it decomposes.

Inoculant Groups Explained

Group G – Lupin & Serradella

Designed for lupins and serradella. Seedmart’s Group G inoculant contains a compatible Bradyrhizobium strain selected for this crop group.

Group E – Pea, Vetch & Lentil

Used for field peas, vetches and lentils. This group is particularly relevant to cool-season green manure and cover crop plantings.

Group F – Faba Beans

Used with faba beans, broad beans and related Vicia species where compatible rhizobia are required for effective nodulation.

Group AL – Lucerne & Medic

Designed for lucerne, alfalfa and medic species. These perennial and pasture legumes require their own compatible inoculant group.

Group M – Tropical Legumes

Used with selected tropical pasture legumes such as siratro, butterfly pea, puero, velvet bean and related warm-season species.

Group J – Pigeon Pea & Lablab

Designed for summer-growing legumes including pigeon pea, lablab and perennial horse gram.

Do All Legumes Need Inoculation?

Not every planting will respond equally to inoculation. Some soils already contain effective populations of compatible rhizobia, particularly where the same legume or a closely related host has been grown successfully in recent years.

Inoculation Is Particularly Worth Considering When

  • The legume has not previously been grown in the paddock or garden
  • The crop has not been grown successfully for several years
  • The site has poor history of legume nodulation
  • The soil has been disturbed or substantially altered
  • A reliable nitrogen-fixing green manure crop is the objective

Existing Rhizobia May Already Be Present When

  • The same compatible legume has been grown successfully recently
  • Previous crops developed abundant active nodules
  • The soil has a long history of that legume group
  • Environmental conditions have supported rhizobia survival

Inoculation is inexpensive insurance for many legume plantings. Where there is uncertainty about whether suitable rhizobia are already present, applying the correct inoculant before sowing can improve the likelihood of effective nodulation.

How to Apply Legume Inoculant

  1. Confirm the correct inoculant group.
    Check that the inoculant is compatible with the legume species you are planting.
  2. Prepare the seed immediately before sowing.
    Work in a shaded location and keep the seed, inoculant and treated seed away from excessive heat and direct sunlight.
  3. Lightly moisten the seed.
    Use clean water or a suitable sticking solution so the inoculant can adhere evenly to the seed surface.
  4. Add the inoculant.
    Mix gently until the seed has an even coating. Use the recommended amount for the quantity of seed being treated.
  5. Protect the treated seed.
    Do not leave inoculated seed exposed to sunlight, heat or drying conditions.
  6. Sow promptly.
    Plant treated seed as soon as practical after inoculation so the living bacteria have the best chance of remaining viable.
  7. Maintain suitable soil moisture.
    Good germination and early root development help create conditions in which the rhizobia can colonise the roots.

Typical Seed Treatment Rates

Application rates vary by product, but Seedmart’s current inoculant packs are generally designed around the following treatment quantities.

Inoculant Quantity Approximate Seed Quantity Treated Typical Use
5 g Up to approximately 2.5 kg seed Smaller garden, trial and green manure plantings.
25 g Up to approximately 12.5 kg seed Medium-sized plantings and larger green manure projects.
50 g Up to approximately 25 kg seed Larger seed lots and agricultural sowings.

Always check the individual product page and inoculant packaging before treatment, as application rates and product specifications may change.

Keeping Rhizobia Alive

Legume inoculants contain living microorganisms. Their effectiveness depends not only on choosing the correct strain but also on keeping the bacteria viable until the treated seed reaches suitable soil.

Keep Cool

Store inoculant refrigerated where possible and avoid leaving packets in hot vehicles, sheds or direct sunlight.

Protect from Sunlight

Rhizobia are sensitive to ultraviolet light. Treat seed in the shade and keep inoculated seed protected before sowing.

Avoid Drying

Once the inoculant is applied, sow the seed promptly rather than allowing treated seed to sit exposed for extended periods.

Check the Expiry Date

Inoculants are biological products with a limited storage life. Use fresh product within the manufacturer’s recommended period.

Heat can quickly reduce inoculant viability. Do not leave rhizobium inoculant or freshly treated seed sitting in direct sun, on hot machinery or inside a hot vehicle before sowing.

Can Inoculated Seed Be Mixed with Fertiliser?

Direct contact between freshly inoculated seed and some fertilisers or chemical seed treatments can reduce rhizobia survival. Where fertiliser is being applied at sowing, placement and compatibility should be considered carefully.

Protect the Inoculant

  • Avoid prolonged direct contact with fertiliser
  • Avoid incompatible chemical seed treatments
  • Do not expose treated seed to excessive heat
  • Keep seed shaded between treatment and sowing
  • Sow treated seed promptly

Plan the Sowing Operation

  • Treat only the quantity that can be sown promptly
  • Check fertiliser placement before planting
  • Follow product-specific compatibility instructions
  • Use clean mixing equipment
  • Keep inoculant refrigerated until required

Inoculants and Green Manure Crops

Legume inoculants are particularly relevant to green manure and cover crop systems because legumes are often included specifically for their ability to fix atmospheric nitrogen.

Peas, vetches, lupins, serradella, lucerne, medics, pigeon pea and lablab can all contribute to soil-building rotations when suited to the climate and inoculated with the correct rhizobia where required.

Planning a soil-building crop? Browse our green manure and cover crop seeds for legumes, grasses, brassicas and multi-species mixtures suited to Australian gardens, farms and regenerative landscapes.

Nodulation and Nitrogen Fixation Are Not the Same Thing

The presence of nodules is a useful sign that rhizobia have colonised the plant, but simply finding nodules does not automatically mean they are fixing nitrogen effectively.

Nodulation Effective Nitrogen Fixation
Rhizobia have infected the root and formed nodules. The nodules are actively converting atmospheric nitrogen into forms available to the plant.
Nodules may vary in size, number and location. Healthy active nodules often show pink or reddish colouring internally when cut open.
Poorly functioning nodules may still be present. Effective fixation also depends on suitable soil, moisture, temperature and plant health.
Nodule formation confirms interaction between rhizobia and the plant. Strong fixation requires a compatible strain and favourable growing conditions.

Other Factors That Affect Nodulation

Using the correct inoculant is important, but inoculation alone cannot overcome unsuitable soil or severe environmental stress.

Soil pH

Strongly acidic or alkaline conditions can affect rhizobia survival, nutrient availability and legume growth. Tolerance varies between strains and crops.

Soil Moisture

Dry soil can reduce rhizobia survival and delay establishment, while prolonged waterlogging can restrict root development and oxygen availability.

Temperature

Both the host plant and rhizobia have preferred temperature ranges. Crops planted outside their normal season may establish poorly.

Soil Nitrogen

Very high levels of readily available nitrogen can reduce the plant’s reliance on biological nitrogen fixation and may suppress nodulation.

Frequently Asked Questions

What is legume inoculant?

Legume inoculant is a preparation containing living rhizobia bacteria selected for particular legumes. When compatible bacteria colonise the roots, they can form nodules and establish the biological process that allows the plant to fix atmospheric nitrogen.

Does one inoculant work for every legume?

No. Different legumes require particular rhizobia strains or inoculant groups. Always match the inoculant to the crop being planted.

Which inoculant do I need for lupins?

Seedmart’s Group G inoculant is intended for compatible lupins and serradella species, including narrow leaf lupin and selected serradellas.

Which inoculant do I need for peas and vetch?

Field peas, vetches and lentils generally use Seedmart’s Group E inoculant.

Which inoculant do I need for broad beans?

Faba beans, broad beans and related species use Group F inoculant.

Which inoculant do I need for lucerne?

Lucerne, alfalfa and compatible medic species use Group AL inoculant.

Which inoculant should I use for lablab or pigeon pea?

Seedmart’s Group J inoculant is designed for pigeon pea, lablab and related compatible legumes.

Do I need to inoculate legumes every year?

Not necessarily. Compatible rhizobia may persist in soil where the same host legumes have been grown successfully. However, survival varies with soil type, climate, pH, cropping history and environmental conditions, so inoculation is often recommended where reliable nodulation is important or there is uncertainty about rhizobia populations.

How soon after inoculating should I sow the seed?

Inoculated seed should generally be sown as soon as practical. Rhizobia are living bacteria and their survival declines when treated seed is exposed to heat, sunlight or drying conditions.

Should legume inoculant be refrigerated?

Yes. Store inoculant refrigerated where possible and follow the storage directions supplied with the product. Avoid heat and direct sunlight.

Can I use expired inoculant?

Using fresh inoculant within its labelled expiry period provides greater confidence that an adequate population of viable rhizobia remains in the product.

Can I mix inoculated seed with fertiliser?

Direct contact with some fertilisers can harm rhizobia. Check the inoculant and fertiliser instructions and avoid prolonged contact between freshly inoculated seed and potentially damaging fertiliser products.

How can I tell whether a legume has nodulated?

Carefully dig up established plants rather than pulling them from the soil and examine the roots for nodules. Effective active nodules commonly show pink or reddish colouring internally when cut open, although appearance varies between crops and growing conditions.

Does inoculant add nitrogen directly to the soil?

No. The inoculant supplies compatible rhizobia bacteria rather than nitrogen fertiliser. Nitrogen fixation occurs through the symbiotic relationship between the bacteria and a suitable living legume plant.

Legume inoculants for Australian growers

Support Nodulation and Biological Nitrogen Fixation

Seedmart supplies rhizobium inoculants for legumes used in gardens, green manure crops, cover cropping, pasture establishment and larger agricultural plantings throughout Australia.

Choose the inoculant group that matches your crop, keep the product cool and protected from sunlight, and sow freshly inoculated seed promptly. Review the individual product pages above for current pack sizes, application rates and crop compatibility before ordering.