Biological nitrogen fixation efficiency in brazilian common bean genotypes as measured by 15N methodology.
2017
FRANZINI, V. I. | MENDES, F. L. | MURAOKA, T. | TREVISAM, A. R. | ADU-GYAMFI, J. J.
Common bean (Phaseolus vulgaris L.) represents the main source of protein for the Brazilian and other Latin-American populations. Unlike soybean, which is very efficient in fixing atmospheric N2 symbiotically, common bean does not dispense with the need for N fertilizer application, as the biologically fixed N (BNF) seems incapable to supplement the total N required by the crop. A experiment under controlled conditions was conducted in Piracicaba, Brazil, to assess N2 fixation of 25 genotypes of common bean (Phaseolus vulgaris L.). BNF was measured by 15N isotope dilution using a non-N2 fixing bean genotype as a reference crop. The common bean genotypes were grown in low (2.2 mg N kg-1 soil) or high N content soil (200 mg N kg-1 soil), through N fertilizer application, as urea-15N (31.20 and 1.4 atom % 15N, respectively). The bean seeds were inoculated with Rhizobium tropici CIAT 899 strain and the plants were harvested at grain maturity stage. The contribution of BNF was on average 75% of total plant N content, and there were differences in N fixing capacity among the bean genotypes. The most efficient genotypes were Horizonte, Roxo 90, Grafite, Aporé and Vereda, when grown in high N soil. None of the genotypes grown in low N soil was efficient in producing grains compared to those grown in high N soil, and therefore the BNF was not able to supply the total N demand of the bean crop.
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