GRDC code

DAN00097

For maximum N benefits from legumes, they must be well nodulated. For the majority of situations, farmers will need to inoculate the seed or soil with the appropriate strain of rhizobia at sowing in order to ensure good levels of nodulation. In other situations, however, there will be adequate numbers of effective rhizobia already in the soil and inoculation will have no effect on either nodulation or crop growth. The NSW Department of Primary Industries and other state Departments of Agriculture take the conservative approach and recommend that all legumes are inoculated at sowing. There are far less problems with unnecessary inoculation than not using inoculants when they are needed. Unnecessary inoculation represents a small cost of production; N-deficient crops can mean substantial reduction in yield and income.

Inoculant brands and formulations

Until recently, the commonly-used method for inoculation was to apply a peat-based inoculant, produced and marketed by just one or two manufacturers, as a slurry to the seed just before sowing. Now, a more diverse range of inoculant products with different modes of application are available from a larger number of manufacturers:
• Becker Underwood (NODULAID™, NODULATOR™) – Peat, liquid and granular inoculants. The peat and liquid inoculants applied as a slurry/powder/liquid to the seed or ‘in furrow’ to the soil. The attapulgite clay granular inoculants applied ‘in furrow’ to the soil. A new product, BioStacked®, is likely to be available in 2009. BioStacked® is an inoculant containing rhizobia plus a plant-growth promoting (PGP) bacteria.
• New-Edge Microbials (EasyRhiz™, Nodule N™)) – The peat and freeze-dried inoculants applied as a slurry/powder/liquid to the seed or ‘in furrow’ to the soil.
• ALOSCA Technologies (ALOSCA®) – Bentonite clay granular inoculants, applied ‘in furrow’ to the soil.
• Brushmaster (Inoculeze™) – Peat inoculants, applied as a ‘tea’ extract to the seed just before sowing using an applicator.
• Novozymes Biologicals Australia (N-Prove™) – Peat, liquid and granular inoculants. The peat and liquid inoculants applied as a slurry/powder/liquid to the seed or ‘in furrow’ to the soil. The peat granular inoculants applied ‘in furrow’ to the soil. It is likely that Novozymes will release TagTeam®, an inoculant containing rhizobia plus a phosphorus solubilising fungus, Penicillium bilaii, in 2009.
All of the products listed above incorporate the same strain of rhizobia for each of the legume groups (e.g. Mesorhizobium ciceri strain CC1192 is used by all manufacturers for chickpea, and so on). The inoculant strains are selected on the basis of exhaustive laboratory, glasshouse and field research by the state Departments of Agriculture, CSIRO and a number of the universities. Fresh cultures of the strains are supplied annually to the manufacturers by the NSW DPI’s Australian Legume Inoculants Research Unit (ALIRU).

Quality assurance of inoculants and inoculant quality

As well as supplying fresh rhizobial cultures to the inoculant manufacturers, ALIRU conducts a substantial amount of independent quality testing of inoculants at both the point-of-manufacture and the point-of-sale. This is in addition to the internal QA conducted by the companies themselves. During 2007, ALIRU tested 96 batches of inoculants at manufacture with >95% pass rate. Failed batches were withdrawn from sale. In the same year, ALIRU tested 280 samples at the point-of-sale with 95% pass rate. Another 4% just failed the standard.

Nodulation failures do occur with commercial legume sowings, although infrequently. In some cases, it is impossible to pinpoint the exact cause of the failure. In many cases, the problem is associated with poor application of the inoculant, rather than inoculant quality. Application problems include:
• Toxic chemicals on the seed causing death of the rhizobia
• Delay in sowing, resulting in the death of the rhizobia inoculated onto seed
• Low volumes of water, i.e. <50 L/ha, used to apply inoculants ‘in furrow’
• The wrong inoculant used for a particular legume
• Very hot, dry conditions (air and soil) when sowing causing death of the rhizobia

Farmers should always follow the label instructions. Seed should be sown as soon as possible after inoculation, i.e. within 4 hours. If sowing is delayed for more than a day, the farmer should consider re-inoculating the seed. The inoculant should never be mixed with chemicals toxic to the rhizobia. If in doubt about the chemical, contact the inoculant manufacturer. If possible, inoculated legumes should be sown into cool-warm, moist soil, rather than hot, dry soil.

Granular inoculants

Granular inoculants, also called soil or solid inoculants, were developed at least 40 years ago and have been widely used in the U.S. for at least 25 years (Bezdicek et al. 1978; Brockwell et al. 1980). Essentially the granules are a peat prill or a solid, inert core such as clay coated or impregnated with rhizobia. Rates of application are generally 5–10 kg/ha, with the inoculant delivered into the seed row from a box (e.g. a pesticide box) on the sowing frame. Major advantages of granular inoculants are ease of storage, handling and application. Soil inoculation using granules separates the rhizobia from toxic, seed-applied chemicals and seed-coat compounds. Disadvantages are the bulk of the granules with the high rates of application (5–10 kg/ha versus 0.25 kg/ha for peat inoculants), the increased transport costs and problems if the granules are not free-flowing.

Although not a new technology, granular inoculants have only become available to Australian farmers during the past 5 years. In 2002–4, ALOSCA Technologies developed and released a bentonite clay granular inoculant for the WA grains belt with small amounts finding their way across to the southern and northern grains regions. More recently Becker Underwood and Novozymes (formerly Philom Bios Australia) have begun to trial and market granular products, based on attapulgite clay and peat, respectively.

Overseas experience with granular and peat and inoculants

In North America (Canada and the U.S.), published reports indicate that granular inoculants applied directly to the soil are generally superior to peat slurry-on-seed inoculation. In four field studies, granular inoculants produced an average 20% more grain yield than the seed-applied peat inoculants (Bezdicek et al. 1978; Muldoon et al. 1980; Rice and Olsen, 1992; Clayton et al. 2004). This enhanced efficacy of the granules, coupled with their other advantages (see above), have undoubtedly led to their widespread use by Canadian and U.S. farmers.

Australian experience with granular and peat inoculants

Brockwell et al. (1980), in early research in Australia on granular inoculants, reported equivalent nodulation and yields of legumes inoculated with granular and seed-applied peat inoculants. When the seed was dressed with fungicides toxic to the rhizobia, however, soil inoculation with granules or peat suspended in water (liquid inoculation) produced as much as 7 times the nodulation and 50% more yield than seed inoculation.

More recent trials (2003–8), for the most part conducted by scientists of the Victorian Department of Primary Industries at Rutherglen, indicate substantial variability in quality of the granular inoculants tested and a strong relationship between numbers of rhizobia in the inoculant and legume nodulation (Matt Denton, Vic DPI, personal communication). Best results were achieved with the high-count inoculants. Results from these trials and from the ALIRU point-of-sale surveys of inoculant quality indicate the need for more consistency of rhizobial counts in some of the products.

The bottom line

A farmer’s choice of inoculant will depend to a large extent on personal experience and product availability, relative cost and perceived efficacy. The commercial inoculant manufactures, Rhizobium scientists with the state Departments of Agriculture, the universities and CSIRO, as well as GRDC, work together to ensure than Australian farmers continue to have access to very high-quality legume inoculants. Peat inoculant, applied to the legume seed as a slurry, remains the most widely used of the formulations and the benchmark for efficacy. Under the right conditions, the freeze-dried formulation is highly efficacious. The clay and peat granular inoculants, applied directly to the soil, are appealing to farmers because of ease-of-use and convenience and in the future may well supplant peat as the inoculant formulation of choice. New co-inoculant products, such as TagTeam® and BioStacked®, are exciting new products that promise yield increases and improved gross margins under certain conditions. Whilst the potential benefits of all formulations and products may be real and appealing, farmers should look for evidence of efficacy in their particular environment. They should also use the products strictly according to the label.

References

Bezdicek DF, Evans DW, Abede B, Witters RE (1978) Evaluation of peat and granular
inoculum for soybean yield and N fixation under irrigation. Agronomy Journal, 70, 865-868.
Brockwell J, Gault RR, Chase DL, Hely FW, Zorin M, Corbin EJ (1980) An appraisal of practical alternatives to legume seed inoculation: field experiments on seed bed inoculation with solid and liquid inoculants. Australian Journal of Agricultural Research, 31, 47-60.
Clayton GW, Rice WA, Lupwayi NZ, Johnston AM, Lafond GP, Grant CA, Walley F (2004) Inoculant formulation and fertilizer nitrogen effects on field pea: crop yield and seed quality. Canadian Journal of Plant Science, 84, 89-96.
Muldoon JF, Hume DJ, Beversdorf WD (1980) Effects of seed- and soil-applied Rhizobium japonicum inoculants on soybeans in Ontario. Canadian Journal of Plant Science, 60, 399-409.
Rice WA, Olsen PE (1992) Effects of inoculation method and size of Rhizobium meliloti population in the soil on nodulation of alfalfa. Canadian Journal of Soil Science, 72, 57-67.

Contact details

David Herridge
NSW Department of Primary Industries
Tamworth Agricultural Institute, 4 Marsden Park Rd, Calala, NSW 2340
Ph: 02 6763 1143
Fx: 02 6763 1222
Email: david.herrige@dpi.nsw.gov.au