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: Matthew D Denton 1 David J Pearce 2 and Mark B Peoples 3
1 The University of Adelaide, School of Agriculture, Food and Wine, Adelaide SA 5005
Australlia
2 Department of Primary Industries, RMB 1145 Chiltern Valley Road, Rutherglen, VIC
3685, Australia
3 CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601 Australia
Presentation Title: The influence of rhizobial inoculant application rate on nitrogen fixation in faba bean
(Vicia faba l.) In south eastern Australia
Presentation Time: 1700 – 1720
Nodulation of legumes is essential to create effective nitrogen fixing symbioses, yet the need to inoculate pulses
with large numbers of effective rhizobia is often not appreciated. In this study, we tested the influence of seven
rates of rhizobia inoculation, from no inoculant to 100 times the normal rate of inoculation, on the responses of
faba bean in two fields in south-eastern Australia: one site with no detectable rhizobia and one with 2900 rhizobia
g -1 soil. Rhizobia inoculation increased nodule numbers from 0 to 55 nodules per plant and nodule dry matter
(DM) from 0 to 330 mg. The increase in nodule numbers directly impacted on fixed N, which increased from 20 to
218 kg shoot N ha -1 , and on grain N concentrations, which increased from 3.2 to 4.5%. An increase in N2 fixation
was even observed in the presence of a soil population when a high rate of inoculation was provided. Increases
in nodulation improved grain yields by around 1.0 t ha -1 in well-nodulated treatments (2.6 t ha -1 ) compared with
those of un-inoculated faba bean (1.6 t ha -1 ) at the site without rhizobia present in soil. Differences in nodulation
also influenced the contributions of legume N to the system, which varied from the removal of 20 kg N ha -1 from
the system to an input of 199 kg N ha -1 . This study illustrates the importance of inoculation to N2 fixation, grain
yield, grain N concentration and the potential contributions of legume cropping to soil N fertility. The study also
identifies the need for technologies to increase inoculant numbers supplied to legumes as a pathway to improve
N2 fixation by legumes that are sown into fields with existing rhizobial populations.
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