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Dinitrogen fixation of soybean and alfalfa: comparison of the isotope dilution and difference methods
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The sutdy compared non-nodulating soybean [Glycine max (L.) Merr.] and ineffectively nodulating alfalfa (Medicago sativa L.) as controls for the isotope dilution technique (IDT) and difference method (DM) with their normal, effectively nodulated counterparts in field experiments on a soil with high and low available N. Dry matter production and distribution, and partitioning of total N and 15N in the N2-fixing and non-fixing counterparts of each species were investigated. The agreement and precision of the IDT and DM using whole plant compared with shoot samples were determined. The N2-fixing and non-fixing isolines of soybean and the two populations of alfalfa were similar in dry matter, total N, and 15N partitioning in the plant and individual organs when both species were grown at high available soil N. Under lower available soil N, differences in dry matter, total N, and 15N partitioning occurred between the roots and seeds of the soybean isolines but not between the organs of the alfalfa populations. Inclusion of roots and nodules is not necessary for accurate estimation of N2-fixation. The differential partitioning of 15N among organs of the soybean isolines was of no importance to measurement of N2-fixation by IDT at individual harvests or over the entire season. The DM will probably underestimate N2-fixation compared to the IDT and will also be less precise. [AS/SS]
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 Record created 1985-06-03, last modified 2019-03-04

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