By Associate Professor John Howieson and Ron Yates, Centre for Rhizobium
Studies, Murdoch University
Large-scale trials later this year will build on the promising results
achieved from a better method of inoculating rhizobia into soils, using
dry clay granules as the carrier.
Nitrogen fixation with legumes and rhizobia is worth $2 billion annually
to Australian agriculture. To protect and enhance this asset, rhizobial
research in southern Australia has put great effort into selecting inoculant
quality Rhizobium strains capable of high nitrogen fixation and with excellent
survival in soils.
Most of this research has been funded by the GRDC and delivered through
the National Rhizobium Program. This program has delivered rhizobial inoculant
strains of very high quality to farmers for the rapidly growing suite
of pulse and pasture legumes in Australian agriculture.
Traditional peat-based inoculants currently used by growers have practical
limitations. To help overcome the problem, Bay Classic Pty Ltd are collaborating
with researchers at the Centre for Rhizobium Studies to develop an alternative
inoculant and delivery system – dry clay granules.
With peat-based inoculants, Rhizobium cells start dying immediately after
the peat is removed from the protective packet (which has been held at
4°C). The death rate may be rapid for some strains and slower for
others. Manufacturers are successfully managing this mortality by producing
peat inoculants with very high counts, that still deliver sufficient numbers
of rhizobia on seed to produce nodulation under most conditions.
However, to achieve this, the legume seed has to be sown immediately
after inoculation into moist soil. Compounding the rapid death rates,
particularly with pulses, is the toxicity of fungicide dressings applied
to seed. This has substantially restricted the way farmers may inoculate
and sow legumes with respect to timing of the operation. In contrast to
peat inoculants, air-dried clay granules hold rhizobia in a state of “suspended
Cells do not die rapidly, so the granules can be stored in the shed under
ambient conditions and then drilled with the seed or fertiliser. This
gives farmers total control of legume inoculation and greater fl exibility
with regards to the time of sowing.
About 25 experiments were conducted around Western Australia in 2003
with very promising results. Granules achieved similar nodulation patterns
to conventional peat inoculant at most sites, and better nodulation where
the legumes were sown into marginal moisture. It is planned to release
the dry clay granules in pre-commercial quantities for “proof of
concept” trials on farmers’ properties in 2004.
For more information:
Associate Professor John Howieson, 08 9360 2231, email@example.com
Bay Classic Pty Ltd, 08 9756 6121, firstname.lastname@example.org
GRDC RESEARCH CODE UMU00003, program 4