IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Wednesday 30 November 2011
Concurrent Session 13 - Inoculant Quality & Application
1600 - 1740
Authors: Ron Yates 1,2 , Angelo Loi 1 , Brad Nutt 1 & John Howieson 2
1 Department of Agriculture and Food, Western Australia (DAFWA), Baron Hay Court,
South Perth, 6151, Western Australia.
2 Centre for Rhizobium Studies (CRS), Murdoch University, Murdoch, 6150, Western
Australia.
Presentation Title: How do we ensure nodulation of annual pasture legumes sown out of season into hot,
dry soil?
Presentation Time: 1620 – 1640
Biological nitrogen (N) fixation from effectively nodulated legumes are an integral component of sustainable
agriculture. Agricultural legumes not only provide N for subsequent crops and high value feed for animals, they
also assist in spreading the risk in the production system through the management of weeds, pests and
diseases. In Australia, it is essential legumes are inoculated with the correct and current commercial rhizobia
strain (or Group) for maximum N fixation. Commercial inoculant strains go through an extensive selection
process, in which the strains must possess the ability to maintain high N fixation over a broad host range and
adapt to the anticipated soil niche of the host legume. However, an ongoing challenge is to successfully deliver
high numbers of the commercial inoculant. If this is not achieved it leads to failed nodulation, or nodulation of the
legume with resident soil-borne strains that are usually sub-optimal in N fixation.
Inoculants in Australia are available in four different carriers: (i) peat; (ii) freeze dried powders; (iii) granular; and
(iv) a pre-coated seed form, with inoculum as part of the pellet. The efficiencies of these products are continually
being evaluated for use in Western Australian agriculture. However, current research is largely focused on
providing best practices for inoculating pasture legumes when they are introduced by “Summer sowing” in the
Mediterranean climates of southern Australia (i.e. when the soil is hot and dry). This technique has been
designed to cheaply introduce legume species into paddocks at a time when farm labour is not limiting, assisted
by strategically harnessing inherent hard-seed breakdown in the legume cultivars. However this presents a
challenge in terms of keeping the inoculant rhizobia alive until a rainfall event that induces germination, and
identifying which carrier is the most efficient at doing so. Summer sowing requires the bacteria to survive through
dry, hot, soil conditions in sufficient number to out-compete resident strains for nodulation when the seeds
germinate, which may be up to four months after sowing. Recent findings will be presented that suggest
surprising outcomes in rhizobial survival.
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