Inoculating legumes: A practical guide
Nitrogen (N) fixed by the soil bacteria rhizobia symbiotically with Australia’s pasture and pulse legumes, has a national benefit of close to $4 billion annually. This is based on nitrogen fixation rates of about 110 kilograms of N per hectare per year, legume areas of 25 million ha and fertiliser N costed to the grower at $1.25/kg, which equates to $1.55/kg plant-available N in the soil. The price of carbonbased fossil fuels, used in the production of nitrogenous fertilisers, is expected to increase substantially in the future. As this occurs, the value of legume nitrogen fixation to Australian growers will escalate.
There is an ongoing need to ensure that Australian agriculture evolves with a reliance on legumes that are effectively nodulated and that the benefits of nitrogen fixation from legumes for farming systems are maximised.
This will not occur if legume nodulation is sub-optimal, because of one or more of the following factors:
- growers do not inoculate when they should;
- growers use inoculation practices that do not deliver sufficient rhizobia to the developing legume seedling;
- growers use inoculants of sub-optimal quality;
- legume breeding programs release cultivars that are not matched with highly effective rhizobial inoculants;
- ineffective populations of rhizobia evolve in the soil and outcompete effective inoculant rhizobia;
- inoculant rhizobia are exposed to chemical toxicities during inoculation or soon after application to the soil; and
- populations of soil rhizobia in regenerating pastures decline because the landscapes become hostile through soil salinity, acidity or for other reasons.
To capitalise on the potential benefits of legume nodulation and nitrogen fixation, Australian growers need to:
- understand the role of legumes in supplying N to agricultural production systems;
- manage legume nitrogen fixation and system N supply for maximum productivity and sustainability;
- inoculate legumes where and when appropriate;
- optimise inoculation outcomes through correct use of the inoculant product;
- understand the limitations of inoculants, e.g. death of the rhizobia from exposure to toxic and dehydrating conditions;
- have access to the most efficacious inoculant products in the marketplace;
- understand the specific nature of the relationship between legumes and rhizobia and use the appropriate inoculant strain for a target legume-host;
- grow the most appropriate legume in terms of environment and soil biology; and
- manage soils to minimise plant growth-limiting factors (e.g. pathogens, heavy metals, low pH, salinity).
This handbook was written by a group of Australian experts in the field of rhizobiology and nitrogen fixation from universities and state departments of agriculture and primary industries, many of whom work within the National Rhizobium Program (NRP), to address the above issues. The NRP is a GRDC R&D program, funded in three phases between 1998 and 2012, with objectives to address the science that underpins the above issues.
The major geographic focus of the handbook is the wheat-sheep belt (essentially 100% of Australia’s grain production and >50% of wool production), with a minor focus on the high-rainfall belt (about 30% of Australia’s wool production).
The key audiences are growers, grower groups, commercial and government advisers, agribusiness, research agronomists, legume breeders, seed pelleters, resellers and seed merchants. It is intended that material from this handbook can be extracted and used in training workshops. Workshops would need to be tailored to the particular group. For example, the material used in workshops for individual growers/grower groups may be different for seed pelleters.
By using the handbook and/or after participating in workshops that use materials from the handbook, users should have an increased knowledge of legumes and legume nodulation in farming systems, should more effectively use inoculation as a key farm practice, and should have achieved higher farm productivity through enhanced legume nitrogen fixation and system N supply.
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Elizabeth Drew, David Herridge, Ross Ballard, Graham O’Hara, Rosalind Deaker, Matthew Denton, Ron Yates, Greg Gemell, Elizabeth Hartley, Lori Phillips, Nikki Seymour, John Howieson and Neil Ballard
Grains Research and Development Organisation
Grains Research and Development Organisation
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