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    Estimation of symbiotic N2 fixation associated with large perennial plant species, especially trees, poses special problems because the process must be followed over a potentially long period of time to integrate the total amount of fixation. Estimations using isotope dilution methodology have begun to be used for trees in field studies. Because of the special problems of trees, certain precautions should be taken in the experimental design of isotope dilution studies. The fixing and non-fixing species should be interplanted so that each is exposed to the same changes in soil environment over the duration of the study. Under most circumstances, 15N enriched fertilizer should be applied to the soil in a miniplot around which there has been placed a plastic film barrier to prevent the tree roots from gaining access to unlabelled N outside of the treated area differentially. A concurrent study of biomass accumulation and tissue N content should be undertaken to ensure that both the fixing and non-fixing species are physiologically similar and that N recycling is not influencing the accuracy of estimates of N2 fixation. Formulas for estimation are presented that take into account the special needs of tree studies.

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    Baker, Dwight D.; Fried, Maurice; Parrotta, John A. 1995. Theoretical implications for the estimation of dinitrogen fixation by large perennial plant species using isotope dilution. pp. 225-236 in: Nuclear Techniques in Soil-Plant Studies for Sustainable Agriculture and Environmental Preservation. International Atomic Energy Agency/FAO, Vienna, Austria.


    nitrogen fixation, isotope dilution, 15N enrichment, methodologies, tropical trees, Leucaena leucocephala, Casuarina equisetifolia

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