SEEDS ENRICHED WITH PHOSPHORUS AND MOLYBDENUM IMPROVE THE CONTRIBUTION OF BIOLOGICAL NITROGEN FIXATION TO COMMON BEAN AS ESTIMATED BY 15N ISOTOPE DILUTION

Seeds with a high concentration of P or Mo can improve the growth and N accumulation of the common bean (Phaseolus vulgaris L.), but the effect of enriched seeds on biological N-2 fixation has not been established yet. This study aimed to evaluate the effect of seeds enriched with P and Mo on growth and biological N-2 fixation of the common bean by the N-15 isotope dilution technique. An experiment was carried out in pots in a 2x3x2x2 factorial design in randomized blocks with four replications, comprising two levels of soil applied P (0 and 80 mg kg(-1)), three N sources (without N, inoculated with rhizobia, and mineral N), two seed P concentrations (low and high), and two seed Mo concentrations (low and high). Non-nodulating bean and sorghum were used as non-fixing crops. The substrate was 5.0 kg of a Red Latosol (Oxisol) previously enriched with N-15 and mixed with 5.0 kg of sand. Plants were harvested 41 days after emergence. Seeds with high P concentration increased the growth and N in shoots, particularly in inoculated plants at lower applied P levels. Inoculated plants raised from high P seeds showed improved nodulation at both soil P levels. Higher soil P levels increased the percentage of N derived from the atmosphere (%Ndfa) in bean leaves. Inoculation with the selected strains increased the %Ndfa. High seed P increased the %Ndfa in inoculated plants at lower soil P levels. High seed Mo increased the %Ndfa at lower soil P levels in plants that did not receive inoculation or mineral N. It is concluded that high seed P concentration increases the growth, N accumulation and the contribution of the biological N-2 fixation in the common bean, particularly in inoculated plants grown at lower soil P availability.