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This article in AJ

  1. Vol. 79 No. 3, p. 505-509
    Received: May 12, 1986

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Nitrogen Fixation and Translocation in Field-Grown Fababean1

  1. F. Zapata,
  2. F. Danso,
  3. G. Hardarson and
  4. M. Fried2



Fababean (Vicia faba L. var. minor) has high N requirements for optimum yields. There are some indications that this legume can satisfy a greater part of this requirement largely through biological N2 fixation. To confirm these observations, more quantitative estimates of N2 fixed in fababean on different soils and over different seasons are necessary. Also, detailed N nutrition and translocation studies could serve as the basis for any required improvement in N2 fixation. This study assessed the contribution of soil, fertilizer, and fixed N2 to the nutrition and growth of fababean at seven growth stages. The soil used is classified as a Typic Eutrocrept. The A-value approach, involving the application of 20 and 100 kg N/ha of l5N-labeled ammonium sulphate to fababean and spring wheat (Triticum vulgare) as a reference crop, respectively, was used to assess the relative contributions of N from fixation, soil, and fertilizer to plant growth. At physiological maturity harvest (126 days after planting), fababean had accumulated 209 kg N/ha, 79% of which was derived from fixation, with about 20% coming from soil and 1% from the labeled fertilizer. These results confirm that fababean has the ability for high N2 fixation. Growth and N2 fixation were, however, low during early growth (0–59 days after planting), but increased rapidly after this period. The maximum N2 fixation rate was achieved between the early and mid-pod-filling stages, an interval during which N2 fixation accounted for more than 4 kg N/ha/day. The N2 fixation activity dropped to almost zero after the mid-podfilling stage. After the mid-pod-filling stage, the N demand of the developing seeds and pods was higher than could be satisfied through the negligible soil uptake of N and N2 fixation. Thus, N translocated from the shoot was virtually the only source for pod and seed development at these final stages. With such a high level of N2 fixation in fababean, it was estimated that after grain removal, fababean growth led to a net positive residual N level in soil.

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