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Advantages and Disadvantages of Nitrogen-15 Isotope Dilution to Quantify Dinitrogen Fixation in Field-Grown Legumes-A Critique

2013; Linguagem: Inglês

10.2136/sssaspecpub18.c4

2165-9826

R. J. Rennie,

Agronomic Practices and Intercropping Systems

Problems associated with accurately quantifying dinitrogen (N2) fixation in field-grown annual legumes have impeded progress in selecting superior strains of rhizobia, legume cultivars, and agronomic conditions that reduce dependence on fertilizer and soil N. Although 15N isotope dilution is not without its limitations, if the basic assumptions of the procedure are accepted and experimentally evaluated, it provides the most reproducible and precise estimate of percent N2 fixed and N2 fixation in field-grown annual legumes. It determines rates of N2 fixation integrated over the entire period of plant growth while simultaneously indicating the three possible N sources (atmosphere, soil, and fertilizer) which, under the plant's genetic control, contribute to its yield and permit the plant to attain its genetic yield potential. A major drawback of isotope dilution to the present date is that it is a totally destructive analytical technique.