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Agronomy Journal Abstract -

Dinitrogen Fixation Measured by 15N Isotope Dilution in Two Canadian Soybean Cultivars1


This article in AJ

  1. Vol. 74 No. 4, p. 725-730
    Received: Nov 23, 1981

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  1. R. J. Rennie,
  2. S. Dubetz,
  3. J. B. Bole and
  4. H. H. Muendel2



Adapted cultivars must be developed if significant production of soybeans [Glycine max (L.) Merr.] is to be realized in western Canada. Selection and breeding for ability to support symbiotic N2 fixation is important in this development.

15N isotope dilution techniques were used to determine the percent plant N derived from the atmosphere (%Ndfa), i.e., fixation, and actual amounts of N fixed by two promising cultivars, X005 and Maple Presto. Precent Ndfa for the two cultivars was almost identical under comparable conditions. Depending on soil type and plant growth stage, %Ndfa varied from 38 to 70% in lysimeter experiments and maximized at 67% in the field. X005 fixed significantly more N2 (115 kg N/ha) than Maple Presto (82 kg N/ha) in the field because X005 had a higher N yield, possibly due to a slightly longer growing season. The N yield of both cultivars, when inoculated, did not respond to increasing rates of fertilizer N [Ca (NO3)2]. The highest percent fertilizer use efficiency (%FUE) was 51% when uninoculated and 44% when the seed was inoculated. Although N2 fixation occurred in both cultivars when fertilizer up to 160 kg N/ha was provided, the cultivars differed in their tolerance to fertilizer N with respect to N2 fixation. For X005, N2 fixation was constant as N fertilizer increased from 0 to 80 kg/ha but decreased by 24% where 160 kg N/ha was applied. For Maple Presto, N2 fixation was constant as N fertilizer increased from 0 to 40 kg/ha but decreased by 21% where 80 or 160 kg N/ha was applied. Both cultivars had similar %Ndfa and amount of N fixed/ha to soybeans in other countries.

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