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    An estimation of biological nitrogen fixation by Leucaena leucocephala (Lam.) de Wit in monoculture and mixed-species plantations (with Casuarina equisetifolia L. ex J.R. & G. Forst., and Eucalyptus robusta Sm.) was undertaken over a two-year period in Puerto Rico using the 15N-enrichment methodology. Foliage from Leucaena and Eucalyptus (the reference species) was sampled at selected intervals between applications of 15NĀ­enriched fertiliser and the N-isotopic composition was used to estimate the proportion of N derived from nitrogen fixation (pNdfa) and total N derived from nitrogen fixation (tNdfa). The influence of different foliage sampling strategies.(i.e. leaf age and canopy position) on the estimation of nitrogen fixation by the method was also evaluated. Leucaena was estimated to obtain approximately 80% of its nitrogen from fixation (pNdfa) at 12 and 18 months, and approximately 10% at 24 months. No consistent differences in pNdfa were noted for Leucaena among monoculture and mixed-species treatments. Although differences in isotopic composition were observed among leaf samples from different canopy positions and between older and younger leaves, similar estimates of pNdfa were obtained provided the same canopy positions and leaf ages were sampled for both the nitrogen-fixing and reference species. We estimated that nitrogen fixation (tNdfa) in these two-year-old plantations was 5.1 to 7.1 g N m-2 yr-1 for Leucaena in mixed-species plots and 10.3 g N m-2 yr-1 in the Leucaena monocultures.

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    Parrotta, John A.; Baker, Dwight D.; Fried, Maurice. 1994. Estimation of nitrogen fixation in Leucaena leucocephala using 15N-enrichment methodologies. pp. 75-82 in: Sprent, Janet I. and McKey, Doyle. (eds.) Advances in Legume Systematics, 5: the Nitrogen Factor. Royal Botanic Gardens, Kew, UK.


    nitrogen fixation, tropical trees, 15N-enrichment, Leucaena leucocephala, Puerto Rico

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