Plant and Soil

, Volume 82, Issue 3, pp 397–405 | Cite as

Effect of plant genotype and nitrogen fertilizer on symbiotic nitrogen fixation by soybean cultivars

  • G. Hardarson
  • F. Zapata
  • S. K. A. Danso


Isotopic as well as non-isotopic methods were used to assess symbiotic nitrogen fixation within eight soybean [Glycine max (L.) Merr.] cultivars grown at 20 and 100 kg N/ha levels of nitrogen fertilizer under field conditions.

The15N methodology revealed large differences between soybean cultivars in their abilities to support nitrogen fixation. In almost all cases, the application of 100 kg N/ha resulted in lower N2 fixed in soybean than at 20 kg N/ha in the first year of the study. However, N2 fixed in one cultivar, Dunadja, was not significantly affected by the higher rate of N fertilizer application. These results were confirmed by measurements of acetylene reduction activity, nodule dry weight and N2 fixed as measured by the difference method. Further proof of differences in N2 fixed within soybean cultivars and the ability of Dunadja to fix similar amounts of N2 at 20 and 100 kg N/ha was obtained during a second year experiment. Dunadja yield was affected by N fertilizer and produced larger yield at 100 kg N/ha than at 20 kg N/ha. This type of cultivar could be particularly useful in situations where soil N levels are high or where there is need to apply high amounts of N fertilizer.

The present study reveals the great variability between legume germplasms in the ability to fix N2 at different inorganic N levels, and also the potential that exists in breeding for nitrogen fixation associative traits. The15N methodology offers a unique tool to evaluate germplasms directly in the field for their N2 fixation abilities at different N fertilizer levels.

Key words

Acetylene reduction Glycine max L. Merr. N-difference method N2 fixation 15N methodology Rhizobium japonicum Soybean 


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Copyright information

© Martinus Nijhoff/Dr W. Junk Publishers 1984

Authors and Affiliations

  • G. Hardarson
    • 1
  • F. Zapata
    • 1
  • S. K. A. Danso
    • 2
  1. 1.FAO/IAEA Agricultural Biotechnology LaboratorySeibersdorfAustria
  2. 2.Joint FAO/IAEA DivisionViennaAustria

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