Populations of Sinorhizobium meliloti congregate in the 30–60 cm section of the soil profile in a stand of dryland lucerne (Medicago sativa): is this where lucerne fixes its nitrogen?
C. M. Evans A B D , N. A. Fettell A and J. Brockwell CA NSW Department of Primary Industries, Agricultural Research and Advisory Station, PO Box 300, Condobolin, NSW 2877, Australia.
B Present address: Central West Farming Systems, PO Box 171, Condobolin, NSW 2877, Australia.
C CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
D Corresponding author. Email: catherine.evans@agric.nsw.gov.au
Australian Journal of Experimental Agriculture 45(3) 225-230 https://doi.org/10.1071/EA03149
Submitted: 29 July 2003 Accepted: 28 January 2004 Published: 14 April 2005
Abstract
Lucerne (Medicago sativa L.) cv. Hunterfield was inoculated with Sinorhizobium meliloti and sown in a red clay loam at Condobolin, New South Wales. The soil had been limed at 6 different rates 8 years previously. In 2001, when the stands were 3 years old, the populations of S. meliloti were enumerated, with a plant-infection test, in 4 sections of the soil profile (i.e. 0–15 cm, 15–30 cm, 30–60 cm and >60 cm). The numbers of rhizobia in the soil were very high (120 000 rhizobia/g) in the 30–60 cm section. In sharp contrast, much lower numbers (0–15 cm, 75 rhizobia/g; 15–30 cm, 190 rhizobia/g; >60 cm, 287 rhizobia/g) were detected in the other sections of profile. Liming had no effect on size of S. meliloti population. It was concluded that, under the conditions of the experiment, it was reasonable to assume that lucerne nodulated most abundantly between 30–60 cm below ground. This zone may represent the location of maximum nitrogen fixation. Some implications of the conclusions are discussed.
Additional keywords: alfalfa, dryland pastures, nitrogen fixation, nodulation, rhizobia.Sinorhizobium meliloti
Acknowledgments
We thank Geraldine O’Neill for her contribution to sampling soil and rhizobia. The work was partly supported by funding from the Grains Research and Development Corporation.
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