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

Abstract

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.

Effect of soil interacting herbicides on soybean nodulation in Balcarce, Argentina

“…Differences in nodulation atributes between treated and control plots (Figs. 2 and 3) were not evident on yield or N accumulation, probably because the soybean plants assimilated more soil N to compensate for eventually lower N 2 fixation rates as demonstrated by Rennie et al (1982) and Rennie & Dubetz (1984).…”

Peanut Cultivar Responses to Bradyrhizobium Inoculation in Northeast Thailand

“…The ARA procedure was performed on freshly dug root systems as described by For the 1986 experiment, total nitrogen and N-15 content of the plant material was determined on the plants within the N-15 labelled microplots at maturity. Preparation of the plant material, Kjeldahl digestions and mass spectrometer determination of N-15 in the plant material were as described by Rennie et al (14). Isotope terminology and calculations used are according to Rennie et al (16).…”

INFLUENCE OF SINGLE STRAINS AND A COMMERCIAL MIXTURE OF Bradyrhizobium japonicum ON GROWTH, NITROGEN ACCUMULATION AND NODULATION OF TWO EARLY-MATURING SOYBEAN CULTIVARS

“…Matthews and Hayes (1982) reported that in Great Britain, low RT restricted the growth of inoculated and noninoculated soybean, but the inoculated plants were much more affected. At RT (Rennie et al 1982).…”

“…Consequently, proper inoculation is required for efficient soybean production @ailey 1981; Rennie et al 1982 RESULTS AND DISCUSSION Soil temperature increased from 5'C (1 May) to a maximum of 24"C (I8 July), then decreased to 15'C by 13 Sept. (Fig. 1).…”