Plant and Soil

, Volume 102, Issue 2, pp 291–294 | Cite as

Theoretical considerations in the comparison of total nitrogen difference and13N isotope dilution estimates of the contribution of nitrogen fixation to plant nutrition

  • Segundo S. Urquiaga
  • Robert M. Boddey
Short Communications


In the estimation of the contribution of biological nitrogen fixation (BNF) to plant nutrition many authors have compared the estimates derived from the15N-isotope-dilution technique with those derived from the total N-difference technique. In this paper we show that agreement of these two estimates is mathematically inevitable when the recovery of labelled nitrogen (%FUE) by the “N2-fixing” (test) and control plants is equal, and that this agreement does not constitute an independent confirmation of the BNF estimate derived from one technique by the other. Even if different quantities of15N labelled fertilizer are added to the test and control crops (the A-value technique), but the % FUE for the two crops is the same, then again the BNF estimate derived from the A-value calculations will inevitably agree with the total N difference estimate.

Key words

A-value isotope dilution nitrogen fixation quantification 15


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Copyright information

© Martinus Nijhoff Publishers 1987

Authors and Affiliations

  • Segundo S. Urquiaga
    • 1
  • Robert M. Boddey
    • 1
  1. 1.EMBRAPA-Programa Nacional de Pesquisa em Biología do SoloRio de JaneiroBrazil

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